Genitourinary Imaging

Question 1

Retroperitoneal Anatomy

Answer 1

Anterior pararenal space - ascending colon, descending colon, (2nd and 3rd) duodenum,and pancreas

Perirenal space: surrounds each kidney - kidneys, proximal ureter, adrenals, and lots of fat.

Posterior perirenal space - potential space, contains only fat, may become secondarily involved in inflammatory processes.

The retroperitoneum can be separated into three compartments by the anterior and posterior renal fascia and the lateral conal fascia.

The adrenals and kidneys are locatedwithin the perirenal space of the retroperitoneum.

The ascending and descending colon, the second and third portions of the duodenum, and the pancreas are located in the anterior pararenal space of the retroperitoneum.

The third compartment of the retroperitoneum, the posterior pararenal space, is a potential space that is clinically important as a pathway for potential disease spread due to secondary involvement of inflammation or neoplasm.

Question 2

Liposarcoma

Answer 2

Liposarcomas are a diverse group of neoplasms that make up the most common primary retroperitoneal tumors. 10-15% of all liposarcomas arise from the retroperitoneum.

The most common type of liposarcoma is the well-differentiated group, which is composed of adiopocytic, sclerosing, and inflammatory subtypes. Adipocytic liposarcoma resembles a lipoma, predominantly composed of fat with strands of tissue representing collagen bands.

In order of increasing malignancy, liposarcomas may also be myxoid, round-cell, pleomorphic, or dedifferentiated. The more aggressive subtypes may have minimal or no areas of macroscopic fat and may be indistinguishable from other malignant soft-tissue masses.

Question 3

Retroperitoneal fibrosis

Answer 3

Retroperitoneal fibrosis is a rare inflammatory disorder causing increased fibrotic deposition in the retroperitoneum, often leading to ureteral obstruction.

Unlike malignant retroperitoneal adenopathy, retroperitoneal fibrosis tends not to elevate the aorta off the spine.

Question 4

Adrenal Glands Anatomy

Answer 4

The adrenal glands are inverted Y-shaped endocrine glands, which primarily mediate the stress response by releasing cortisol and catecholamines. The adrenals are also a site of secondary sex hormone synthesis and blood pressure regulation (with aldosterone).

The two distinct components to the adrenal glands are the cortex and the medulla, which are derived from completely different embryological origins (the cortex is derived from mesothelium; the medulla is derived from neural crest) and are susceptible to different diseases.

Question 5

Adrenal cortex

Answer 5

The adrenal cortex synthesizes the steroid hormones aldosterone, glucocorticoids, and androgens, which are all biochemical derivatives of cholesterol.

Each of the three layers of the adrenal cortex synthesizes one type of hormone: Zona glomerulosa (most superficial): Produces aldosterone. Zona fasciculata: Produces glucocorticoids in response to pituitary adrenocorticotropic hormone (ACTH). Zona reticularis (deepest; closest to the adrenal medulla): Produces androgens.

Pathology of the adrenal cortex that can be diagnosed on imaging includes adrenal hyperplasia, adrenal adenoma, and adrenal cortical carcinoma.

Question 6

Adrenal medulla

Answer 6

The adrenal medulla is the central portion of the adrenal gland and produces the catecholamines norepinephrine and epinephrine, which are derived from tyrosine.

Pathology of the adrenal medulla includes pheochromocytoma and the neuroblastic tumors (ganglioneuroma, ganglioneuroblastoma, and neuroblastoma). Neuroblastoma is the most common extracranial solid tumor of childhood and is discussed in the pediatric imaging section.

Question 7

Adrenal hyperfunction

Answer 7

Cushing syndrome is excess cortisol production from non-pituitary disease, such as idiopathic adrenal hyperplasia, adrenal adenoma, or ectopic/paraneoplastic ACTH (e.g., from small cell lung cancer).

Cushing disease is excess cortisol production driven by excessive pituitary ACTH.

Conn syndrome is excess aldosterone production, most commonly from an adrenal adenoma, which causes hypertension and hypokalemia. The adenomas implicated in Conn syndrome are typically small and may be difficult to detect on CT. Localizing the side of excess hormone production with venous sampling may be a helpful diagnostic adjunct.

Question 8

Adrenal Hypofunction

Answer 8

Significant destruction of the adrenals is required to produce adrenal insufficiency.

Although usually not an imaging diagnosis, Addison disease represents chronic adrenocortical insufficiency and may be caused by autoimmune destruction of the adrenal glands or as a sequela of infection.

Waterhouse-Friderichsen syndrome is post-hemorrhagic adrenal failure secondary to Neisseria meningitidis bacteremia.

Idiopathic adrenal hemorrhage is usually unilateral and rarely causes adrenal hypofunction.

Question 9

Adrenal adenoma

Answer 9

Adrenal adenoma is a benign tumor of the adrenal cortex. Adenomas are usually incidental, but they may occasionally produce excess aldosterone to cause secondary hypertension (Conn syndrome). Non-contrast imaging of the adrenal glands is the best test to evaluate for the presence of an adrenal adenoma in the presence of suspicious clinical symptoms or lab values.

A common clinical scenario is the need to differentiate between an adrenal adenoma and an adrenal metastasis in the staging of a patient with known malignancy. The diagnosis of an adenoma is made by the detection of intracellular lipid.

An adrenal nodule attenuating = 10 Hounsfield units (HU) an be reilably diagnosed as an adenoma with no further imaging or follow-up needed. Most (80%) adenomas are lipid-rich and will attenuate below this cutoff. Up to 20% may be lipid-poor adenomas, which attenuate >10 HU and are not able to be diagnosed on a noncontrast CT. An indeterminate (>10 HU), small, homogenous adrenal lesion in a patient without a known malignancy is overwhelmingly likely to represent a lipid-poor adenoma, and advanced imaging is usually not required in such cases.

If the nodule in question attenuates > 10 HU and clinical confirmation of an adenoma is necessary for clinical management (for instance, in a patient with lung cancer and no evidence of metastatic disease but with an indeterminate adrenal nodule), then an adrenal washout CT or in- and out-of-phase MRI may be helpful to characterize the lesion.

A collision tumor represents metastasis into an adrenal gland with a pre-existing adenoma. If an “adenoma” appears heterogenous or has shown an interval icnrease in size, then a collision tumor should be considered in a patient with a known primary even if a region attenuates < 10 HU.

Adenomas contain intracytoplasmic lipid due to steroid production. MRI is able to detect even a small amount of intracystoplasmic lipid that may be undetectable on CT by taking advantage of the fact that protons resonate at different frequencies in fat and in water. Chemical shift imaging consists of images obtained both in-phase and out-of-phase. When fat and water are contained within the same voxel, out-of-phase images show fat drop-out of signal because fat protons are more shielded and resonate at a slower frequency. Chemical shift imaging is based on T1 images.

Adenomas suppress on out-of-phase images, while metastases generally do not.

A short list of malignancies do contain intractyoplasmic lipid and thus would also lose signal on out-of-phase images: Well-differentiated adrenocortical carcinoma (very rare). Clear cell renal cell carcinomas metastatic to the adrenal gland. Hepatocellular carcinoma metastatic to the adrenal gland. Liposarcoma (typically a predominantly fatty mass that is rarely confused with adrenal adenoma.)

Question 10

CT Imaging: Adrenal Washout CT

Answer 10

Adrenal adenomas demonstrate more rapid contrast washout than metastases do. The more rapid contrast washout of benign adenomas appears to be true even compared to adrenal metastases of hypervascular primaries.

The timing of the washout phase remains controversial, with recent evidence suggesting 15-minute washout has greater sensitivity than 10 minutes.

> 60% absolute washout is diagnostic of adenoma

If unenhanced CTis not available or not performed due to concern for radiation exposure, >40% relative washout is diagnostic of adenoma.

In a patient with a known primary malignancy, lesions that do not demonstrate benign washout kinetics are suspicious for, but not diagnostic of, metastasis.

Question 11

Role of biopsy of an adrenal mass

Answer 11

Adrenal mass biopsy is indicated for an indeterminate adrenal mass after full imaging workup remains nondiagnostic.

Biopsy is safe and generally very accurate.

Question 12

Myelolipoma

Answer 12

An adrenal myelolipoma is a benign neoplasm consisting of myeloid cells (i.e., erythrocyte precursors - not “myo” as in muscle) and fat cells.

An adrenal mass with any discrete focus of macroscopic fat is virtually diagnostic of a myelolipoma. Exceedingly rare cases of adrenocortical carcinoma and metastatic carcinoma have been reported to contain macroscopic fat. A retroperitoneal liposarcoma may mimic a myelolipoma, although liposarcoma typically presents as a large mass that may displace, rather than arise from, the adrenal.

An adrenal myelolipoma should not be confused with a renal angiomyolipoma (AML). These two entities are unrelated, although they do have similar names, are located in adjacent organs, and are both diagnosed by the presence of macroscopic fat.

Question 13

Adrenal cyst

Answer 13

Adrenal cysts are uncommon but have imaging characteristics typical of cysts elsewhere (thin, smooth, nonenhancing wall, and water-attenuation internal contents).

Endothelial adrenal cysts are the most common (45%) type and may be lymphatic or angiomatous in origin.

Pseudocysts are rare, comprising only 9% of adrenal cysts.

Occasionally an adrenal cyst may have a complex appearance that may be difficult to differentiate from a cystic/necrotic neoplasm. In such a case, percutaneous aspiration or surgical resection may be considered.

Small, asymptomatic, simple cysts can be ignored. A cyst may rarely grow so large as to cause symptoms, such as dull pain or compression of the stomach/duodenum, in which case surgery may be indicated.

Very rarely, hydatid disease may affect the adrenal glands, typically producing a complex lesion with an internal membrane.

Question 14

Pheocromocytoma: Potentially malignant

Answer 14

Pheochromocytoma is a neoplasm of chromaffin cells, usually arising from the adrenal medulla. Pheochromocytoma may cause hypertension and episodic headaches/diaphoresis.

The “rule of 10’s” is a general rule characterizing the features of pheochromocytoms: 10% are extra-adrenal. 10% are bilateral. 10% are malignant. 10% are familial or syndromic.

Pheochromocytoma is associated with several syndromes: Multiple endocrine neoplasia (MEN) 2A and 2B: Typically bilateral intra-adrenal pheochromocytomas. Von Hippel-Lindau. Neurofibromatosis type 1. Carney’s triad (gastric leiomyosarcoma, pulmonary chondroma, and extra-adrenal pheochromocytoma).

An extra-adrenal pheochromocytoma is a paraganglioma. The most common intra-abdominal location of a paranglioma is the organ of Zuckerkandl, located at the aortic bifurcation. A rare intra-abdominal location of a paraganglioma is the bladder, producing the distinctive clinical presentation of post-micturition syncompe (syncope after urination).

Paragangliomas occur in the head and neck in characteristic locations. Paragangliomas of the head and neck are generally called glomus tumors and may be associated with the tympanic membrane (glomus tympanicum), the jugular foramen (glomus jugulare), the carotid body (called a carotid body tumor), or the vagus nerve (glomus vagale).

Nuclear medicine studies can be used in the workup of pheochromocytoma. Of note, I-123 MIBG is used for metastatic workup of adrenal pheochromocytoma and Indium-111 pentetreotide (an analog of octreotide) is used as tracer for localization of a paraganglioma.

In theory, pheochromocytoma should be diagnosed by urine/plasma metanephrines before imaging is performed, with imaging used for localization and staging. In clinical practice, CT is often employed based on suspicious symptoms (such as episodic hypertension or other symptoms of catecholamine excess).

The classic MRI appearance of pheochromocytoma is a hyperintense mass on T2-weighted images. When large, pheochromocytoma may appear heterogenous on MRI and CT.

Question 15

Adrenal cortical carcinoma

Answer 15

Adrenal cortical carcinoma is a very rare malignancy, with a prevalence of approximately 1/1,000,000. Approximately 66% are functional, producing a disordered array of hormones that may manifest as Cushing syndrome, hyperaldosteronism, and virilization

Adrenal cortical carcinoma usually presents on imaging as a large, heterogenous mass. Central necrosis and hemorrhage are typical.

Question 16

Metastasis

Answer 16

Autopsy studies show adrenal metastases are present in > 25% of patients with a known primary. Lung cancer and melanoma are the most common adrenal metastases.

Question 17

Lymphoma

Answer 17

Primary adrenal lymphoma is rare.

Question 18

Adrenal hyperplasia

Answer 18

Adrenal hyperplasia is caused by prolonged stress response or ectopic ACTH secretion.

Question 19

Adrenal hemorrhage

Answer 19

Adrenal hemorrhage can be spontaneous or due to anticoagulation. When secondary to anticoagulation, the hemorrhage typically occurs within the first few weeks of beginning anticoagulation. Hemorrhage involves the right adrenal gland more commonly than the left.

Hemorrhage may appear mass-like and is often of heterogenous attenuation on CT. The most important clue is a new adrenal mass within a short time interval if priors are available.

Hemorrhage does not enhance and decreases in size on follow-up studies.

Question 20

Adrenal calcification

Answer 20

Adrenal calcification rarely causes adrenal hypofunction. Adrenal calcification can be due to Wegener granulomatosis, tuberculosis, histoplasmosis, or old hemorrhage.

Question 21

Renal mass protocol multiphase CT

Answer 21

A renal mass protocol CT consists of at least three phases of data acquisition, with each phase providing important information to aid in the diagnosis of a renal mass.

Unenhanced phase: necessary as a baseline to quantify enhancement.

Nephrogenic phase (100 second delay): The nephrogenic phase is the critical phase for evaluating for enhancement, comparing to the unenhanced images.

Pyelographic phase (15 minute delay; also called the excretory phase): The pyelographic phase is helpful for problem solving and to diagnose potential mimics of cystic renal masses. The pyelographic phase can distinguish between hydronephosis (will show dense opacification in the pyelographic phase) and renal sinus cysts (will not opacify).

Reflux nephropathy may cause a dilated calyx that can simulate a cystic renal mass on the nephrogenic phase. The pyelographic phase would show opacification of the dilated calyx. The pyelographic phase is also useful to demonstrate a calyceal diverticulum and to show the relationship of a renal mass to the collecting system for surgical planning.

Optionally, a vascular phase can be performed for presurgical planning.

Question 22

Evaluating enhancement (CT and MRI) (Renal Mass)

Answer 22

The presence of enhancement is the most important characteristic to distinguish between a benign and malignant non-fat-containing renal mass ( a lesion containing intralesional fat is almost always a benign angiomyolipoma, even if it enhances).

On CT, enhancement is quantified as the absolute increase in Hounsfield units on post-contrast images, compared to pre-contrast: <10 HU: No enhancement; 10-19 HU: Equivocal enhancement; >/= 20 HU Enhancement.

Lesions are considered “too small to characterize” if the lesion diameter is smaller than twice the slice thickness. For instance, using 3 mm slices, a lesions less than 6 mm cannot be accurately characterized based on attenuation or enhancement.

Question 23

Renal Mass biopsy

Answer 23

After full imaging workup is complete, there are several well-accepted indications for percutaneous renal mass biopsy:

• To distinguish renal cell carcinoma from metastasis in a patient with a known primary.
• To distinguish between renal infection and cystic neoplasm.
• To definitevely diagnose a hyperdense, homogenously enhancing mass (after MRI has been performed), which may represent a benign angiomyolipoma with minimal fat versus a renal cell carcinoma.
• To definitively diagnose a suspicious renal mass in patient with multiple comorbidities for whom nephrectomy would be high risk.
• To ensure correct tissue diagnosis prior to renal mass ablation.

Question 24

Renal Cell Carcinoma

Answer 24

Renal cell carcinoma (RCC) is a relatively uncommon tumor that arises from the renal tubular cells. It represents 2-3% of all cancers. Risk factors for development of RCC include smoking, acquired cystic kidney disease, von Hippel-Lindau (VHL), and tuberous sclerosis.

Clear cell is the most common RCC subtype (~75%), with approximately 55% 5-year survival.

• Clear cell RCC tends to enhance more avidly than the less common subtypes
• Clear cell can be sporadic or associated with von Hippel-Lindau

Papillary RCC is a hypovascular subtype, with a 5-year survival of 80-90%

• Papillary RCC tends to enhance only mildly due to its hypovascularity
• A renal “adenoma” is frequently seen on autopsy specimens and is a papillary carcinoma = 5 mm.

Chromophobe is the subtype with the best prognosis, featuring a 90% 5-year survival.

Collecting duct carcinoma is rare and has a poor prognosis.

Medullary carcinoma is also rare, but is known to affect mostly young adult males with sickle cell trait. Medullary carcinoma is an extremely aggressive neoplasm, with a mean survival of 15 months, not helped by chemotherapy.

Staging of renal cell carcinoma is based on the Robson system, which characterizes fascial extension and vascular/lymph node involvement. Stages I-III are usually resectable, although the surgical approach may need to be altered for venous invasion (stages IIIA and IIIC)

• Stage I: Tumor confined to within the renal capsule.
• Stage II: Tumor extends out of the renal capsule but remains confined within Gerota’s fascia.
• Stage III: Vascular and/or lymph node involvement. IIIA: Renal vein involvement or IVC involvement. IIIB: lymph node involvement. IIIC: Venous and lymph node involvement.
• Stage IVA: Tumor growth through Gerota’s fascia; Stage IVB: Distant metastasis.

Question 25

Angiomyolipoma

Answer 25

Angiomyolipoma (AML) is the most common benign renal neoplasm, composed of fat, smooth muscle, and disorganized blood vessels. The majority are sporadic, but 40% are associated with tuberous sclerosis (where AMLs are bilateral, with multiple renal cysts).

AML has a risk of hemorrhage when large (>/= 4 cm), thought to be due to aneurysmal change of the vascular elements. Small, asymptomatic AMLs are not typically followed or resected.

An early pathognomonic imaging finding is the presence of macroscopic fat in a non-calcified renal lesion. The non fat-containing portion enhances avidly and homogenously. Calcification is almost never present.

On MRI, the fat component will follow retroperitoneal fat on all sequences and will saturate out on fat-saturated sequences. Intracytoplasmic lipid is not a feature of AML, so there should be no significant drop-out on dual-phase MRI.

Approximately 4% of AMLs will not contain visible macroscopic fat and will appear as a hyperdense enhancing mass. MRI is the next step, with the T2-weighted images the most useful to distinguish from renal cell carcinoma in some cases.

• A T2 hyperintense mass suggests RCC (clear cell subtype) and the patient can proceed to surgery.
• A T2 hypointense mass is nonspecific and can represent either RCC (papillary type) or AML with minimal fat. Although an AML typically would enhance more avidly than a papillary RCC, biopsy is warranted for defnitive diagnosis.

Question 26

Oncocytoma

Answer 26

Oncocytoma is the most commonly resected benign renal mass and has overlapping imaging findings with renal cell carcinoma.

Imaging features can suggest oncocytoma, but imaging features are not specific and cannot be reliably differentiated from RCC. The imaging featrues suggestive of oncocytoma are homogenous enhancement and a central scar.

Complicating the pathologic diagnosis, oncocytic cells can sometimes be found in the rare chromophobe RCC subtype. The pathologist can usually distinguish oncocytoma from the more common clear cell and papillary renal cell carcinoma subtypes.

Question 27

Renal Lymphoma

Answer 27

Primary renal lymphoma is rare, as the kidneys do not contain native lymphoid tissue. However, the kidneys may become involved from hematogenously disseminated disease or spread from the retroperitoneum.

Renal invovlement of lymphoma has several patterns of disease:

• Multiple lymphomatous masses (most common pattern; seen in 50% of cases of renal lymphoma).
• Solitary renal mass.
• Diffuse lymphomatous infiltration, causing nephromegaly.
• Direct extension of retroperitoneal disease.

Question 28

Non-neoplastic solid renal mass

Answer 28

When evaluating a potential renal mass, it’s important to always consider that an apparent solid renal mass may represent a non-neoplastic lesion.

Infection, especially focal pyelonephritis, can masquerade as a solid renal mass. Renal abscess may be difficult to differentiate on imaging from a cystic renal cell carcinoma.

Renal arteriovenous malformation (AVM) will avidly enchance and can mimic a hypervascular renal mass. One clue to the presence of an AVM would be asymmetric enhancement of the renal vein on the affected side, due to early shunting of venous blood.

Question 29

Renal Pseudotumors

Answer 29

Renal pseudotumors are normal variations of renal morphology that may mimic a renal mass.

Hypertrophied column of Bertin: The columns (septa) of Bertin are normal structures that anchor the renal cortex to the hilum and create the separations between the renal pyramids. When hypertrophied, the columns of Bertin may mimic a renal mass.

Persistant fetal lobation/lobulation: In normal fetal development, the fetal kidneys are divided into discrete lobes. Occasionally these lobulations persist in adulthood, producing an indentation of the renal cortex. This indentation can cause an adjacent focal bulge that simulates a renal mass. This pseudomass can usually be distinguished from a true mass by the present of septa of Bertin on either side.

Question 30

von Hippel-Lindau (VHL with renal masses)

Answer 30

von Hippel-Lindau (VHL) is an autosomal dominant multiorgan syndrome caused by a mutation in the VHL tumor suppressor gene on chromosome 3, which leads to cysts and neoplasms in multiple organs.

The primary manifestation of VHL in the genitourinary system is bilateral or multifocal renal cell carcinomas, most commonly the clear-cell subtype.

Other genitourinary manifestations of VHL include multifocal pheochromoctyoma and renal cysts.

Central nervous system manifestations of VHL include hemangioblastoma of the brainstem, cerebellum, or spinal cord.

Pancreatic and hepatic manifestations include malignant neuroendocrine pancreatic tumor, pancreatic tumor, pancreatic serous cystadenoma ( a benign neoplasm), and pancreatic/hepatic cysts.

Question 31

Birt-Hogg-Dube

Answer 31

Birt-Hogg-Dube is an autosomal dominant syndrome of dermatologic lesions, cystic lung disease, and multiple renal oncocytomas and renal cell carcinomas.

Question 32

Tuberous sclerosis (TS)

Answer 32

Tuberous sclerosis is an autosomal dominant neurocutaneous disease caused by a tumor suppressor gene mutation. It manifests clinically with seizures, developmental delay, and (mostly) benign tumors in multiple organ systems.

The most common renal manifestations of tuberous sclerosis is multiple bilateral renal angiomyolipomas (AML). Approximately 50% of patients with TS will have at least one AML.

Renal cyst can be seen in ~25%.

The relative risk of renal cell carcinoma is increased in patients with TS, and occurs in approximately 2-3% of patients. Diagnosis of renal cell carcinoma is complicated by the abnormal kidneys that may have multiple cysts and/or AMLs.

The the heart, the most common neoplasm is a rhabdomyoma. A cardiac rhabdomyoma may be present during fetal life and can be detected by fetal ultrasound.

In the lung, a process of smooth muscle proliferation identical to lymphangioleiomyomatosis can occur, causing cystic replacement of lung parenchyma. It has been suggested that the abnormal smooth muscle in te lung in patients with TS represents genetically identical metastatic smooth muscle from a renal angiomyolipoma.

Question 33

Approach to a cystic renal mass

Answer 33

• A cystic renal mass may be neoplastic or infectious; the most comon entities to cause a cystic renal mass are renal cell carcinoma and renal abscess

Neoplastic differential of a cystic renal mass

• Cystic renal cell carcinoma. Although renal cell carcinoma most commonly presents as a solid renal mass, it can also manifest as a cystic renal mass.
• Multilocular cystic nephroma is a benign cystic neoplasm with enhancing septa that occurs in a bimodal age distribution in baby boys and middle-aged women. A characteristic but nonspecific feature is the propensity to herniate into the renal pelvis, causing hydronephosis. (In adults, multilocular cystic nephroma can be indistinguishable from cystic renal cell carcinoma. In children, multilocular cystic nephroma can be indistinguishable from cystic Wilms tumor.)
• Mixed epithelial and stromal tumor (MEST) is a benign neoplasm composed of epithelial and mesenchymal elements, typically found in middle-aged women. MEST may appear as either a solid or cystic mass.

Non-neoplastic differential of a cystic renal mass

• Renal abscess is a contained purulent collection within the kidney.
• Hemorrhagic renal cyst, which will not have any enhancing component.

Role of MRI in evaluation of a complex cystic renal mass

• MRI has a limited role in the evaluation of a cystic renal mass. The key advantage of MRI is more accurate enhancement characterization, as MRI does not suffer from the CT phenomenon of pseudoenhancement due to beam hardening from adjacent, densely enhancing renal parenchyma. (The increased accuracy of MRI to characterize enhancement is most useful to distinguish a Bosniak IIF from a Bosniak III lesion. Thickening of a septation or cyst wall that shows measureable enhancement defines a Bosniak III lesion. The Bosniak classification is discussed on the following page.)
• MRI is more sensitive for detecting septations compared to CT.
• Calcifications are more difficult to detect with MRI.

Question 34

Simple renal cyst

Answer 34

Simple renal cysts are extremely common, found in approximately 50% of patients over age 50. A simple renal cyst is an incidental lesion that requires no follow-up, even when large.

On CT a simple cyst must attenuate close to 0 Hounsfield units, not contain any enhancing components, and have a thin imperceptible wall.

On MRI, a simple cyst must be hypointense on T1-weighted images, hyperintense on T2-weighted images, and not contain any enhancing component.

Question 35

Renal sinus cyst

Answer 35

Cysts in the renal sinus may be classified as parapelvic and peripelvic cysts. A parapelvic cyst is a renal cortical cyst that herniates into the renal sinus. These cysts are usually large but solitary. Peripelvic cysts, in contrast, are lymphatic in origin and usually small and multiple.

Question 36

Hyperdense cyst

Answer 36

A homogenous renal cyst with an attenuation of >70 Hounsfield units on noncontrast imaging represents a benign hyperdense cyst, likely secondary to prior hemorrhage.

A hyperdense cyst cannot be diagnosed if only post-contrast imaging is available as there is no way to distinguish a hyperdense cyst from an enhancing renal mass.

Question 37

Bosniak classification of cystic renal masses

Answer 37

The Bosniak classification risk-stratifies cystic renal masses, with increasing risk for cystic renal cell carcinoma with increasing Bosniak category. Classification is based on morphology, not size (except for hyperdense cysts in categories II and IIF).

Category I and II: No risk of malignancy. No follow-up necessary.

Category IIF: Small risk of malignancy. Imaging follow-up is needed.

Category III and IV: Surgical lesions, concerning for cystic renal cel carcinoma.

Question 38

Bosniak Category I

Answer 38

Water-attenuation cyst, with a hairline wall and no areas of enhancement. Practically, this classification is never used as such a lesio is simply called a simple renal cyst.

Always benign. No folow up needed.

Question 39

Bosniak Category II

Answer 39

Water-attenuation cyst containing a few (3 or fewer) hairline epta. May contain fine septal calcificatio. No enhancement.

Also includes small (< 3 cm) hyperattenuating cysts without enhancement.

Essentially always benign. No follow-up needed.

Question 40

Bosniak Category IIF

Answer 40

Multiple septa, with minimal smooth thickening (3 mm or less). May have thick and nodular mural calcification.

Walls may slightly enhance.

Also includes large (> 3 cm) hyperattenuating cysts without enhancement.

Usually benign. Radiographic follow-up is recommended, where morphologic change or new enhacement would be concerning for malignancy.

Question 41

Bosniak Category III

Answer 41

Thickened, irregular walls or septa, with measurable enhancement.

Concern for malignancy, but may be benign (e.g., infection, multilocular cystic nephroma). Without comorbidities, treatment is surgical.

Question 42

Bosniak Category IV

Answer 42

Distinguishing features is enhancing nodular component separate from wall or septa.

Clearly malignant. Surgical lesion unless significant comorbidities.

Question 43

Autosomal Dominant Polycystic Kidney Disease

Answer 43

Autosomal dominant polycystic kidney disease (ADPKD) is responsible for 10% of patients on long-term dialysis. Patients typically present in their third to fourth decades, initially presenting with upper abdominal pain and a clinical course of progressive renal failure. The kidneys may become so enlarged as to be palpable. Hypertension and hematuria (thought to be due to nephrolithiasis or rupture of a renal cyst into the collecting system) are common. Approximately one half of patients will have a saccular aneurysm in the circle of Willis.

On imaging, the kidneys are markedly enlarged and feature multiple cysts of varying attenuation or signal intensities due to hemorrhage.

The traditional teaching is that ADPKD does not increase the risk of renal cell carcinoma. However, some authors propose that there is a slightly increased risk. Renal cell carinoma associated with ADPKD tends to ccur at a younger age and is more often bilateral, multifocal, and sarcomatoid. Diagnosis of renal malignancy is complicated by the presence of multiple (often hemorrhagic) cysts and frequently concomitant renal insufficiency, which may preclude the use of intravenous contrast.

Question 44

Acquired cystic kdiney disease (due to end-stage kidney disease)

Answer 44

Dialysis-associated cystic renal disease does have an icnreased risk of rena cell carcinoma (~2-3% prevalence, compared to 1/10,000 prevalence in the general population).

Question 45

Pyelonephritis

Answer 45

Pyelonephritis is infection of renal parenchyma and is the most common bacterial infection of the kidney. The bacteria are ascending from the bladder.

The imaging findings of pyelonephritis are nonspecific and imaging may be normal in up to 75%. Various patterns may be seen, including a unilaterally enlarged kidney, wedge-shaped or striated regions of decreased enhancement, and perinephric stranding. The urothelium may also be thickened and hyperenhancing.

The differential diagnosis of a unilateral enlarged kidney includes pyelonephritis, acute ureteral obstruction, renal vein thrombosis, and compensatory hypertrophy.

A striated nephrogram describes linear lucencies extending from the renal cortex to the medullar on a contrast-enhanced study. The differential diagnosis for a striated nephrogram is similar to that of a wedge-shaped perfusion defect and includes:

Pyelonephritis, Renal infarct, Renal vein thrombosis or vasculitis, Renal contusion (typically focal)., Acute urinary obstruction, Renal tumor (especially lymphoma if infiltratitve), Radiation nephritis

Focal pyelonephritis (previously called focal lobar nephronia) may mimic a renal mass.

Mild hydronephrosis can be seen on the affected side, thought to be due to a bacterial endotoxin causing reduced peristalsis, and should not be confused with obstructive uropathy.

Question 46

Pyonephrosis

Answer 46

Pyonephrosis is the infection of an obstructed collecting system and is colloquially referred to as “pus under pressure”. Treatment is emergent percutaneous nephrostomy.

Question 47

Renal abscess

Answer 47

Renal abscess is a localized purulent collection within the kidney that most commonly results from coalescense of small microabscesses in the setting of acute bacterial pyelonephritis. An abscess may simulate a cystic renal mass.

The treatment is conservative if <3 cm and percutaneous drainage if larger.

Question 48

Emphysematous pyelonephritis

Answer 48

Emphysematous pyelonephritis is a severe renal infection characterized by gas replacing renal parenchyma, caused both by gas-forming organisms and renal infarction.

Emphysematous pyelonephritis is seen almost exclusively in diabetic patients.

Emphysematous pyelonephritis is a surgical emergency, requiring emergent nephrectomy.

Question 49

Xanthogranulomatous Pyelonephritis

Answer 49

Xanthogranulomatous pyelonphritis (XGP) is a chronic renal infection due to obstructing calculi, leading to replacement of renal parenchyma with fibrofatty inflammatory tissue.

Proteus mirabilis and Escherichia coli are the two most common organisms.

The clinical presentation of XGP includes flank pain and nonspecific constitutional symptoms, such as fever and weight loss. Anemia and hematuria are also common.

XGP can be diffuse (85%) or localized. The localized form, also known as “tumefactive XGP”, may mimic a renal mass.

CT is the primary modality for imaging, which demonstrates fatty replacement of the renal parenchyma, marked perinephric inflammatory stranding, and staghorn calculi.

The bear paw sign represents the configuration of the hypoattenuating fibrofatty masses arranged in a radial pattern, reminiscent of a bear’s paw.

Primary differential considerations include acute obstructing calculus with pyonephrosis or renal/transitional neoplasm with calcification.

Treatment is nephrectomy.

Question 50

Renal tuberculosis

Answer 50

Mycobacterium tuberculosis inection of the renal parenchyma results from hematogenous dissemination. Active pulmonary TB is present in approximately 10%.

Although initial renal TB infection typically involves both kidneys, chronic changes tend to be unilateral.

Imaging findings include parenchymal calcification, scarring, papillary necrosis, and infundibular strictures. End-stage renal TB produces autonephrectomy and the characteristic putty kidney appearance, which represents an atrophic, calcified kidney.

Question 51

Nepthrolithiasis and ureterolithiasis

Answer 51

Nephro/ureterolithiasis is a common problem that presents with renal colic. Hematuria is usually present, but may be absent if the stone is completely obstructing. Calcium-containing stones (comprised of calcium oxalate and phosphate, pure calcium oxalate, or the less common pure calcium phosphate stones) together represent 73% of urinary lithiasis.

Uric acid, xanthine, matrix, pure struvite, and indinavir (seen in HIV patients on antiretroviral therapy) stones are lucent on radiographs. Virtually all renal stones are radiopaque on CT except for indinavir stones and the very rare uncalcified matrix stones made of mucin.

Secondary signs of ureteral obstruction from a ureteral stone include ipsilateral hydronephrosis and perinephric stranding surrounding the affected kidney. The soft tissue rim sign helps to distinguish a phlebolith from a ureteral stone. The presence of a small amount of soft tissue surrounding the calcification, thought to represent the edematous ureteral wall, suggests a ureteral stone rather than a vascular calcification.

Question 52

Papillary necrosis

Answer 52

Papillary necrosis is necrosis and sloughing of renal papillary tissue, which clinically can cause gross hematuria and may lead to chronic renal insufficiency.

There are numerous causes of papillary necrosis, most commonly NSAIDs, sickle cell anemia, diabetes, and renal vein thrombosis. The commonly used POSTCARD mnemonic may be helpful to remember all causes: Pyelonephritis, Obstruction, Sickle cell disease, Tuberculosis, Cirrhosis, Analgesics (NSAIDS), Renal vein thrombosis, Diabetes mellitus.

On the delayed phase of CT urography, papillary necrosis causes multiple small poolings of extra-calyceal contrast adjacent to the renal calyces.

Three classic uroradiologic signs of papillary necrosis include the ball on tee sign, lobster claw sign (not to be confused with the bear paw sign of xanthogranulomatous pyelonephritis), and signet ring sign, which describe patterns of papillary excavationg.

The ball on tee sign describes contrast filling a central papillar.

The lobster claw sign describes contrast filling only the periphery of the papilla.

The signet ring sing describes contrast surrounding the sloughed papilla.

Question 53

Delayed (prolonged) nephrogram

Answer 53

A delayed (prolonged) nephrogram describes slow renal parenchymal uptake of intravenous contrast, prolonged enhancement, and delayed urine excretion.

A unilateral prolonged nephrogram can be due to acute ureteral obstruction, renal vein thrombosis, and renal artery stenosis.

Bilateral prolonged nephrograms can be seen in bilateral obstruction, contrast nephropathy, systemic hypertension, and myeloma kidney.

Question 54

Medullary nephrocalcinosis

Answer 54

Medullary nephrocalcinosis represents calcification of the renal medullary pyramids, usually with preserved renal function. Medullary nephrocalcinosis can be caused by:

Hypercalcemic state (e.g. hyperparathyroidism, sarcoidosis, etc).

Medullary sponge kidney (cystic dilation of distal collecting ducts; may be unilateral or segmental).

Distal (type 1) renal tubular acidosis (RTA)

Furosemide therapy in a child.

Question 55

Cortical nephrocalcinosis

Answer 55

Cortical nephrocalcinosis is dystrophic peripheral calcification of the renal cortex, with sparing of the medullary pyramids.

Causes of cortical nephrocalcinosis include: Acute cortical necrosis, Chronic glomerulonephritis, Chronic transplant rejection, Hyperoxaluria, Alport syndrome (hereditary nephropathy and deafness).

Question 56

Cortical necrosis

Answer 56

Cortical necrosis is a rare form of renal injury from acute ischemic necrosis of the renal cortex. Cortical necrosis may lead to cortical nephrocalcinosis. Chronic renal failure develops in up to 50% of patients.

Ischemia may be due to small vessel vasospasm or systemic hypotension. Predisposing factors include hemoytic-uremic syndrome and thrombotic microangiopathy.

Question 57

Extracalcyceal contrast medium

Answer 57

Contrast shouldn’t normally be seen beyond the calyces on excretory urogram. Papillary necrosis, tubular ectasia, and calyceal diverticulum may cuase this appearance.

Tubular ectasia causes paintbrush-like streaks of contrast that extend from the papillae into the tubules on excretory urogram. Medullary sponge kidney is tubular ectasia with associated calcifications of the renal medullary pyramids.

Calyceal diverticulum is an outpouching of the collecting system into the corticomedullary region. A dependent sediment or multiple small stones may be present.

Papillary necrosis, reviously discussed, may also cause extracalyceal contrast.

Question 58

Orgain Injury Scale (OIS) - American Associateion for the Surgery of Trauma (AAST) (Renal)

Answer 58

TheOIS scale from the AAST is the most commonly used system for classifying renal trauma. It is a surgical classification but correlates well with the CT findings.

Grade I injury is by far the most common type of renal injury (95%) and describes a renal contusion or subcapsular hematoma. Treatment is conservative.

Grade II injury is a superficial laceration (<1 cm) or confined to perinephric hematoma, without urinary extravasation. Treatment is conservative.

Grade III injury is a deeper laceration (>1 cm), without urinary extravasation. Treatment is typically conservative. (A potential pitfall of a grade III injury is that a clot at the collecting system may prevent urinary extravasation initially, but urinary extravasation may occur later as the clot is lysed by urinary urokinase).

Grade IV is a deep laceration that extends into the collecting system (causing urinary extravasation), or injury to the renal artery or vein with contained hemorrhage. Urinary extravasation is typically treated with surgical repair to prevent later development of urinoma or abscess formation. Vascular grade IV injury can be treated endovascularly.

Grade V is a shattered kidney, or avulsion of the renal hilum. Treatment is variable but typically surgical.

Question 59

CT description of renal trauma

Answer 59

The OIS classification described above is somewhat limited as there are several important renal injuries, including traumatic renal artery thrombosis, renal artery pseudoaneurysm, and ureteral avulsion (most commonly occuring at the ureteropelvic junction) that are not included in the OIS classification but which can affect prognosis.

Traumatic renal artery thrombosis is due to tearing of the intima, which initiates thrombosis. There is permanent loss of renal function after approximately two hours of ischemia.

Pseudoaneurysm is an arterial injury with a high risk of fatal rupture. On imaging, a pseudoaneurysm will be of similar density to the aorta, with arterial enhancement in the arterial phase and washout on delays. Treatment is endovascular embolization.

Question 60

Page Kidney

Answer 60

A Page kidney (named after the doctor who performed experiments wrapping animal kidneys with cellophane) is a rare cause of secondary hypertension due to prior trauma.

A subcapsular hematoma compresses the renal parenchyma and decreases its blood flow. These altered hemodynamics induce increased renin secretion, which can lead to hypertension. It usually takes several months for hypertension to develop.

Imaging shows a subcapsular hematoma causing deformation and flattening of the kidney.

Percutaneous drainage of the hematoma may be effective treatment.

Question 61

CT urography (CTU) indications and protocol

Answer 61

The goal of CT urography (CTU) is to evaluate the kidneys, ureters, and bladder. The key to successful imaging is to maximally distend and opacify the ureters and bladder.

One of the most common indications for CTU is for the evaluation of microscopic or macroscopic hematuria. Hematuria may be caused by a urinary tract calculus, renal mass (e.g. renal cell carcinoma), or urothelial tumor (e.g., transitional cell carcinoma).

Protocols vary by institution. Typically, patients are given 900 mL of water PO and either 250 mL of IV saline or 10 mg of IV furosemide to optimally distend the ureters and bladder.

In adults >/= 40 years of age, CTU is performed as a three-phase exam: (Unenhances CT of the abdomen and pelvis; Nephrographic phase through the kidneys (100 seconds after IV contrast administration).; Excretory phase of the abdomen and pelvis (15 minutes after IV contrast).)

A split-bolus, dual-phase exam decreases radiation exposure in patiens under age 40: Unenhanced CT of the abdomen and pelvis; Combined nephrographic/extretory phase (8 minutes delay after first IV contrast bolus and 100 seconds after the second bolus).

Question 62

Transistional Cell Carcinoma

Answer 62

Although upper-tract malignancy is rare, transitional cell carcinoma is the most common ureteral neoplasm.

The typical imaging appearance is a single filling defect on CT urography; however, multiple filling defects may be seen in 40%. Less commonly, there may be focal thickening of the ureteral wall. Given the propensity of transitional cell carcinoma for multifocality, the bladder should be evaluated for a synchronous mass.

Question 63

Fibroepithelial polyp

Answer 63

Fibroepithelial polyp is the most common benign tumor of the ureter. It typically affects the proximal ureter. Fibroepithelial polyp features a long stalk and appears as an elongated smooth tubular lesion. CT urography best shows the lesion on the coronal images in the pyelographic phase.

Question 64

Urothelial papilloma

Answer 64

Urothelial papilloma is a rare benign neoplasm that may involve the bladder or ureter. The mass may become quite large and mimic a malignancy.

Question 65

Inverted papilloma

Answer 65

Inverted papilloma is a benign mass with a central core of urothelium.

Question 66

Ureteritis cystica

Answer 66

Ureteritis cystica is a benign response to chronic urinary tract inflammation, such as chronic infection or stone disease. Several small subepithelial cysts are found unilaterally in the proximal third of the ureter and renal pelvis. Ureteritis cystica does not have any malignant potential.

Imaging characteristically shows multiple tiny filling defects in the renal pelvis or ureter.

The same disease entity affecting the bladder is called cystitis cystica, which shows multiple rounded contour defects at the base of the bladder.

Question 67

Leukoplakia (squamous metaplasia)

Answer 67

Leukoplakia, also known as squamous metaplasia, is a rare urothelial inflammatory condition named for the characteristic white patch that is produced. Leukoplakia is not thought to be premalignant when the renal collecting system is involved, although there is an association between squamous cell carcinoma and bladder leukoplakia.

Imaging shows a flat mass or focal thickening of the renal pelvic or ureteral wall that may produce a characteristic corduroy appearance.

Question 68

Malacoplakia

Answer 68

Malacoplakia is an inflammatory condition associated with chronic urinary tract infection (usually Eschericia coli) that is typically seen in middle-aged women. It is not premalignant.

Imaging shows multiple flat filling defects that characteristically involve the distal ureter.

Question 69

Ureteral tuberculosis

Answer 69

Multifocal ureteral stenoses are suggestive of ureteral tuberculosis, even more so if there is also evidence of renal tuberculosis (parenchymal calcification and scarring) and/or ballder tuberculosis (small capacity bladder with a thickened wall).

Question 70

Differential diagnosis of a ureteral filling defect

Answer 70

The primary concern of a ureteral filling defect on CT urography is ureteral malignancy.

Ureteral malignancy, of which transitional cell carcinoma is by far the most common.

Ureteral calculus, which is almost always visible on pre-contrast images.

Blood clot.

Malacoplakia (multiple flat defects).

Leukoplakia

Infectious debris (e.g., a mycetoma)

Sloughed renal papilla

Benign ureteral mass (e.g., fibroepithelial polyp).

Question 71

Ureteropelvic Junction Obstruction (UPJ obstruction)

Answer 71

Obstruction of the ureteropelvic junction (UPJ) can be either primary or secondary to infection, stones, or prior surgery.

Primary UPJ obstruction may be due to a congenital aperistaltic segment of ureter, high insertion of the ureter on the renal pelvis, or crossing vessels causing extrinsic compression.

The key imaging finding is a dilated renal pelvis with a normal caliber ureter.

Question 72

Ureterocele

Answer 72

A ureterocele is a focal dilation of the most distal portion of the ureter that protrudes into the bladder. A ureterocele may be orthotopic or ectopic.

An orthotopic ureterocele is seen with a normally inserting ureter, and is seen most commonly in adults. Orthotopic ureteroceles are also known as simple, adult-type, and intravesicular ureteroceles. Orthotopic ureteroceles are usually asymptomatic.

An ectopic urterocele is seen in the setting of a duplicated collecting system, with ectopic insertion of the upper pole ureter into the bladder, and is usually diagnosed in children.

A pseudoureterocele represents intussusception of the distal ureter into the bladder, which may be due to tumor, radiation cystitis, or ureterovesicular junction stone.

Question 73

Bladder stones

Answer 73

Risk factors for bladder stones include urinary stasis (most commonly bladder outlet obstruction) and chronic inflammation (e.g. from infection or foreign body).

An off-midline bladder stone should raise concern for displacement of the stone by a bladder mass or enlarged prostate, or a stone with a ureterocele or a bladder diverticulum.

Question 74

Bladder Transitional cell Carcinoma

Answer 74

Transitional cell carcinoma is by far the most common bladder cancer. The bladder is the most common site of malignancy in the urinary tract.

TCC is a disease of older adults with a male predominance. Risk factors include smoking and aromatic amines. It presents with painless hematuria.

Bladder cancer spreads through the wall of the bladder. Organ-confined disease can be divided into non-muscle-invasive (70%; typically resected endoscopically) and invasive (25%; typically treated with radical cystectomy/nodal dissection).

Metastatic bladder cancery (5%) is treated with systemic therapy.

The presence of pelvic lymph nodes portends a poorer prognosis.

If bladder cancer is clinically suspected, a negative CT urogram does not obviate the need for cystoscopy.

Question 75

Bladder Adenocarcinoma

Answer 75

Adenocarcinoma of the bladder is rare but is associated with a urachal remnant.

The fetal urachus extends from the bladder dome to the umbilicus. It should be obliterated after birth, but may persist as a urachal anomaly (discussed in the Pediatric imaging section).

Question 76

Bladder Trauma

Answer 76

CT cystography is the standar test to evaluate for suspected bladder rupture.

Full distention of the bladder is necessary to evaluate for bladder rupture. Delayed imaging of an intravenous contrast study with opacification of excreted urine is not sensitive enough, and is not the standard of care.

To perform a CT cystogram, a total volume of at least 350 mL (or as much as the patient can tolerate) of dilute water-soluble contrast (50 mL of IV contrast mixed in 500 mL of warm saline) is instilled into the bladder by gravity, with the bag raised 40 cm above the bladder.

Male patients with bladder injury may have associated ureteral injury. If there is blood at the urethral meatus or if there is gross hematuria, a retrograde urethrogram should be performed prior to Foley catheter placement.

Bladder injury can be classified as extraperitoneal (most common), intraperitoneal, or combined.

Question 77

Extraperitoneal Bladder rupture

Answer 77

Extraperitoneal bladder rupture is defined as rupture of the bladder outside the peritoneal space. Extraperitoneal bladder rupture is at least twice as common as intraperitoneal rupture.

Extraperitoneal bladder ruprture is more commonly associated with pelvic fractures compared to intraperitoneal rupture. Extraperitoneal bladder rupture is typically caused by direct laceration of the bladder by a bone fragment.

The molar tooth sign describes the characteristic inverted U appearance of extravasated contrast in the extraperitoneal space of Retzius, which mimics a molar tooth.

Extraperitoneal bladder rupture is typically managed conservatively by placment of a urinary catheter.

Intraperitoneal bladder rupture occurs with disruption of the bladder dome and peritoneum, causing resultant extravasation of urine into the peritoneal space.

The mechanism of intraperitoneal bladder rupture is thought to be through pressure forces on a full bladder causing bursting at the dome into the peritoneum.

The pathognomonic imaging finding on CT cystogram is intraperitoneal contrast interdigitating between loops of bowel.

Intraperitoneal bladder rupture is typically treated surgically.

Question 78

Male urethral anatomy

Answer 78

Question 79

Prostatic Urethra (posterior urethra) (Male)

Answer 79

The prostatic urethra courses within the prostate and is lined with transitional epithelium

The verumontanum is a prominent ridge of smooth muscle in the posterior portion of the prostatic uretera, and is the site of the paired ejaculatory duct orifices. The verumontanum is also the site of obstruction in posterior urethral valves in children. The prostatic utricle is a Mullerian duct derivative and is the blind-ending male homologue of the uterus and vagina, which is also located at the verumontanum.

Question 80

Membranous urethra (posterior urethra) (Male)

Answer 80

The membranous urethra is the shortest, leas mobile uretheral segment.

The membranous urethra is contained within the urogenital diaphragm, which contains the external urethral sphincter and the paiered Cowper’s glands.

Question 81

Bulbous urethra (anterior urethra) (Male)

Answer 81

The bulbar urethra is the site of drainage of Cowper’s glands.

Question 82

Penile urethra (anterior urethra) (Male)

Answer 82

The penile urethra is the longest urethral segment. It is lined with squamous epithelium.

The distal portion of the penile urethra is dilated at the glans penis. This dilation is called the fossa navicularis.

The glands of Littre are small mucous glands of the penile urethra. Normally, small ducts would be occluded by balloon during a retrograde urethrogram, and therefore would not opacify with injected contrast. The glands of Littre tend to opacify more prominently when inflamed in the setting of urethritis.

Question 83

Retrograde Urethrogram (RUG)

Answer 83

Retrograde urethrogram (RUG) provides excellent evaluation of the anterior urethra and may be performed to evaluate for suspected urethral injury, stricture, or fistula.

To perform a RUG, the fossa naviculares is cannulated with a sterile balloon-tipped catheter that is inflated with 1-2 mL saline. Subsequently, approximately 10 mL of contrast is hand-injected under fluoroscopy.

Question 84

Voiding cystourethrogram (VCUG)

Answer 84

Voiding cystourethrogram (VCUG) best evaluates the posterior urethra and is typically performed for evaluation of bladder and voiding function.

To perform a VCUG, a Foley catheter is sterilely placed in the bladder and subsequently contrast is instilled into the bladder. The patient initiates urination during fluoroscopy.

Question 85

Urethral Stricture

Answer 85

Urethral strictures secondary to sexually transmitted disease (most commonly chronic urethritis from Neisseria gonorrhoea) occur most commonly in the bulbous urethra. A complication of chronic urethral infection is a periurethral abscess, which may result in a urethroperineal fistula.

Post-traumatic saddle injury strictures also tend to occur in the bulbous urethra.

In contrast, an iatrogenic stricture from a Foley catheter tends to occur in the penile urethra at the penile-scrotal junction.

Question 86

Urethral Trauma

Answer 86

In the setting of trauma, if there is blood at the meatus, painful urination, or inability to void, a RUG should be performed emergently. If the RUG shows evidence of urethral injury, a suprapubic catheter is typically placed.

There are five types of urethral injury. Type III is the most common, with disruption of the urogenital diaphragm and rupture of the bulbomembranous urethra. Contrast extravasates both into the pelvis and out into the perineum in a type III injury.

Question 87

Anatomy of the female urethra

Answer 87

The female urethra is much shorter than the male urethra. Unlike the male urethra, the female urethra is not divided into discrete segments.

The paraurethral glands of Skene are homologous to the male prostate aned secrete mucus into the urethra. The proximal third of the urethra is lined by transtional epithelium, while the distal portion is lined with a stratified squamous epithelium.

Question 88

Urethral diverticulum

Answer 88

Urethral diverticulum presents clincially with postvoid dribbling, urethral pain, and dyspareunia. Often, however, the symptoms may be vague and nonspecific.

Diverticula are thought to arise from glandular dilation caused by inflammation and chronic infection of the paraurethral glands of Skene.

Urethral diverticula are prone to develop calculi due to urinary stasis.

Very rarely, adenocarcinoma may develop within a urethral diverticulum.

Question 89

Prostate Anatomy

Answer 89

From an imaging standpoint, there are two components to the prostate that can be resolved on MRI: The peripheral zone and the central gland. The central gland refers to both the central zone and the transtion zone, as they cannot be distinguished on MRI.

In younger men, the central gland is composed mostly of the central zone; however, the transition zone enlarges as benign prostatic hyperplasia develops. These changes result in the central gland becoming predominantly composed of transition zone in older males.

Question 90

Prostate cancer

Answer 90

MRI is able to clearly delineate the prostatic zonal anatomy (central gland versus peripheral zone) with T2-weighted sequences. Imaging is enhanced with an endorectal coil.

MRI is inappropriate for screening due to cost and low sensitivity and specificity.

The typical MRI appearance of prostate cancer is a T2 hypointesne region within the T2 hyperintense peripheral zone.

MRI may not detect all prostate cancer: Some cancer is not hypointense on T2-weighted images, central zone cancers are difficult to detect on T2-weighted images, and cancer conspicuity is decreased if the peripheral zone is not T2 hyperintense.

MRI is also not specific: In addition to prostate cancer, the differential diagnosis of a region of peripheral zone T2 hypointensity includes prostatis, hemorrhage, and involutional changes from androgen-deprivation therapy. Advanced MRI techniques, such as MRI spectroscopy, dynamic contrast-enhanced imaging, and diffusion imaging may increase specificity.

MRI spectroscopy of prostate cancer may show elevated choline and depressed citrate peaks compared to normal prostate.

Dynamic contrast-enhanced MRI typically shows prostate cancer to have early enhancement relative to the peripheral zone.

Prostate cancer typically shows restricted diffusion.

The most important goal of MRI is to distinguish between surgical and nonsurgical disease. Cancer that is contained within the gland (tumor stage T2) is generally amenable to radical prostatectomy, while cancer that has spread outside of the gland (T3 and above) is typically treated non surgically (e.g., anti-androgen and radiation therapy).

T-staging: T1: tumor apparent by biopsy only. T2: tumor confined within the prostate (T2a: < 50% of one lobe; T2b; > 50% of one lobe; T2c: Tumor involves both lobes.) T3: Tumor extends through the prostate capsule. May involve seminal vesicles. T4: Tumor invades adjacent structures other than seminal vesicles.

N-staging: Any regional lymph node metastasis is N1; however, extra-pelvic nodes are M1a.

M-staging: M0: No metastases. M1a: Nonregional lymph nodes; M1b: Bone metastases; M1c: Other metastasis.

Question 92

Uterine Anatomy MRI

Answer 92

T2-weighted MRI can distinguish the three layers of the uterus.

Endometrial stripe: Hyperintense on T2.

Junctional zone (first zone of the myometrium): T2 hypointense

The hypointense T2 signal is due to the extremely compact smooth muscle.

The junctional zone should measure

Outer myometrium: Relatively T2 hypointense, although less so than junctional zone.

Question 94

Adenomyosis

Answer 94

Adenomyosis represents ectopic endometrial glands within the myometrium. In contrast to endometriosis, the ectopic endometrial tissue seen in adenomyosis is nonfunctioning.

Adenomyosis can present with similar symptoms to leiomyomas, with pain and bleeding.

Adenomyosis is best seen on T2-weighted images as a thickened junctional zone (> 12 mm), often with multiple foci of T2 hyperintensity. Borderline thickening of the junctional zone (8-12 mm) may be due to adenomyosis, but is not diagnostic of the condition.

Focal adenomyosis may mimic a leiomyoma, appearing as a localized low-signal mass on T1- and T2-weighted images. Typically, adenomyosis features indistinct margins, in contrast to the characteristically sharp margins of a leiomyoma. However, the imaging features between these two entities do sometimes overlap.

Question 95

Leiomyoma (fibroid)

Answer 95

A leiomyoma, commonly known as a fibroid, is an extremely common benign tumor of smooth muscle, which affects up to 40% of reproductive-age women.

Fibroids are often multiple and may be intramural (within the myometrial wall), submucosal (directly underneath the endometrial mucosa), or subserosal (directly underneath the outer uterine serosa).

Small leiomyomas are hypointense on T2-weighted images due to compact smooth muscle. However, cystic or myxoid degeneration may appear hyperintense on T1-weighted images.

Malignant leiomyosarcoma is very rare and may arise de-novo or from malignant degeneration of a fibroid. Imaging cannot reliably differentiate between leiomyoma and leiomyosarcoma unless clearly malignant behavior is identified (such as invasion of adjacent structures or metastases). In the absence of obvious malignant imaging findings, an unusual-looking fibroid is overwhelmingly likely to represent a degeneratig benign fibroid rather than a leiomyosarcoma.

MRI is often performed for treatment planning prior to uterine artery embolization (UAE). Hemorrhagic or necrotic leiomyomas are not treated effectively by UAE. Surgical myomectomy or hysterectomy would be the preferred treatment in these cases. Additionally, there is less chance of UAE success if an ovarian-uterine artery anastomosis is present.

A uterine contraction may mimic a leiomyoma.

Question 96

Endometrial Carcinoma

Answer 96

Endometrial carcinoma is the most common female gynecologic malignancy and is thought to be caused by prolonged estrogen exposure. Specific risk factors include nulliparity, hormone replacement, and Tamoxifen therapy.

Endometrial carcinoma typically presents with post-menopausal bleeding.

MRI can be used for staging once carcinoma is confirmed by histologic sampling.

The presence and extent of myometrial invasion is key for staging. In a premenopausal patient, an intact junctional zone confirms that there is no myometrial invasion. The junctional zone cannot be distinguished in post-menopausal patients, however. The depth of myometrial invasion highly correlates with the presence of lymph node metastasis.

Post-contrast images demonstrate the tumor with the highest conspicuity, as endometrial cancer enhances less avidly than the surrounding myometrium.

The FIGO (international Federation of Gynecology and Obstetrics) staging of endometrial carcinoma was revised in 2010

Stage I: Tumor confied to the uterus. Stage IA: < 50% of myometrial invasion; stage IB: > 50% myometrial invasion.

Stage II: Spread to the cervical stroma, but tumor still contained within the uterus. Involvement of the endocervical glands only is stage I.

Stage III: Spread to adnexa or uterine serosa (IIIA), vagina (IIIB), pelvic lymph nodes (IIIC1), or para-aortic lymph nodes (IIIC2). Prognosis is worse with para-aortic lymph nodes, even in the absence of pelvic adenopathy.

Stage IVA: Spread to bladder or bowel mucosa.

Stage IVB: Distant metastases or inguinal lymph node spread.

Question 97

Normal cervical T2 zonal anatomy

Answer 97

Endocervical canal: T2 hyperintense due to mucin, analogous to uterine endometrium.

Cervical mucosa: Intermediate T2 signal intensity.

Inner cervical stroma: Very hypointense on T2, analogous to the uterine junctional zone. Unlike the uterine junctional zone, however, the decreased T2 signal is due to compact fibrous tissue, not smooth muscle. The superior aspect of the inner cervical stroma is continuous with junctional zone of the uterus.

Question 98

Cervical Carcinoma

Answer 98

Cervical carcinoma is the third most common gynecologic malignancy, with a steep decline in prevalence over the past 50 years due to screening with Pap smears

A cervical mass > 1.5 cm should be evaluated by MRI for staging. The cervical stroma is the key landmark in the staging of cervical cancer: If tumor extends through the cervical stroma into the parametrium, the cancer is stage IIB and treatement is typically non-surgical. Other key findings to note are involvement of bladder or rectum, which denotes stage IV disease (if shown to extend to the mucosal surface with cystoscopy or endoscopy).

The FIGO (International Federation of Gynecology and Obstetrics) staging of cervical cancer was revised in 2010. The new staging takes into account lymp node involvement.

• Stage I: Confined to cervix or uterus. IA: Microscopic lesion. IB: Clinically viable lesion.
• Stage IIA: Spread to upper 2/3 vagina, without parametrial invasion. Typically treated surgically.
• Stage IIB: Parametrial invasion. Typically treated non-surgically (e.g. brachytherapy).
• Stage IIIA: Spread to lower vagina.
• Stage IIIB: Pelvic sidewall extension, hydronephrosis, or pelvic nodal involvement.
• Stage IVA: Spread to bladder or rectum; Stage IVB: Distant metastasis.

Question 99

Congenital Uterine Anomalies

Answer 99

Mullerian duct anomalies may be a cause of infertility or recurrent pregnancy loss (most commonly in septate uterus). Septate and bicornuate uterus are the most common uterine anomalies, which may be differentiated by MRI. The American Fertility Society classification of Mullerian duct anomalies is discussed in the ultrasound section.

Question 100

Septate Uterus

Answer 100

Septate uterus is caused by incomplete resorption of the septum of fused Mullerian ducts.

A septate uterus has a single external fundus but a fibrous or muscular septation dividing two endometrial canals. Infertility is more common in women with septate uterus compared to bicornuate uterus. Metroplasty (resection of the septum) can be performed hysteroscopically if the septum is fibrous, or via an open approach if the septum is muscular.

Question 101

Bicornuate Uterus

Answer 101

Bicornuate uterus is due to incomplete fusion of the Mullerian ducts.

A bicornuate uterus describes a partially split uterus with two separate uterine fundi. In contrast to a septate uterus, the fundus of a bicornuate uterus pinches inwards > 15 mm.

If treated, metroplasty must be performed transabdominally, which is a more invasive procedure compared to hysteroscopic metroplasty.

Question 102

MRI of the adnexa

Answer 102

MRI can provide additional specificity for adnexal lesions that are indeterminate on ultrasound. Fat and hemorrhage are both hyperintense on T1-weighted images, but fat-suppressed T1-weighted imaging can distinguish between lesions containing fat (such as mature cystic teratoma) and containing hemorrhage (such as an endometrioma).

Question 103

Endometriosis

Answer 103

Endometriosis represents ectopic foci of endometrial tissue that are hormonally responsive and therefore may be composed of blood products of varying ages.

The typical MRI appearance of endometriosis is multiple hyperintense masses on T1-weighted images, which demonstrate shading (a gradient of signal intensity) on T2-weighted images. Endometriosis does not suppress on fat-saturated sequences. Less commonly, endometriosis may appear hyperintense on both T1- and T2-weighted images.

Tiny hemorrhagic endometrial implants may only be apparent as tiny hyperintense foci on T1-weighted images.

A ruptured endometrioma may be a cause of acute pelvic pain and may produce free fluid that is hyperintense on both T1- and T2-weighted images.

Laparoscopy is the gold standard for evaluation of suspected endometriosis.

Question 104

Mature cystic teratoma

Answer 104

Also known as a dermoid cyst, mature cystic teratoma is the most common benign ovarian neoplasm in young women. It is composed of diffferentiated tissue from at least two embryonic cell layers.

A mature cystic teratoma is typically a unilocular cystic structure filled with sebaceous material, hair follicles, and other tissues. Less commonly, a mature teratoma may appear as a heterogenous mass or may be a solid fat-containing mass.

A Rokitansky nodule is a solid nodule projecting into the cyst cavity, from which hair or teeth may arise.

On imaging, the sebaceous intracystic component is typically hyperintense on T1- and T2-weighted images, matching fat intensity. Since both an endometrioma and a teratoma are predominantly hyperintense on T1-weighted images, the fat-suppressed sequences are key to differentiation. Teratoma will show signal loss on the fat suppressed images.

Ovaries containing a dermoid cyst are predisposed to torsion.

Question 105

Ovarian Cancer

Answer 105

Ovarian cancer is the second most common female pelvic malignancy but is one of the most lethal malignancies as 65% of patients present with advanced disease.

MRI is used to characterize indeterminante adnexal masses, rather than for staging.

The presence of a solid enhancing component, intra-lesional necrosis, ascites, or peritoneal nodularity suggests a malignant lesion, although no finding is 100% specific.

MRI is highly sensitive to detect peritoneal implants, which occur most commonly in the pouch of Douglas, paracolic gutters, bowel surface, greater omentum, and liver surface.

Ovarian cancer may be epithelial, germ cell, sex-cord stromal, or metastatic in origin.

Approximately 90% of malignant tumors are of epithelial origin. Serous tumors are the most common epithelial subtype, followed by mucinous, endometrioid, and clear cell.

Serous cystadenocarcinomas are frequently bilateral and typically appear as mixed solid and cystic masses. The solid portions demonstrate avid enhancement. There is often concomitant ascites.

Mucinous cystadenocarcinomas are large, more commonly unilateral, and occur in older patients compared to serous cystadenocarcinomas. Mucinous cystadenocarcinomas typically present as a multiloculated cystic mass containing mucin-rich T1 hyperintense fluid.

Clear cell carcinoma and less commonly endometrioid carcinoma are associated with endometriosis.

Malignant germ cell tumors occur in younger patients and include dysgerminoma, endodermal sinus tumor, and immature teratoma.

Sex-cord stromal tumors include granulosa cell (hormonally active) and Sertoli-Leydig (rare).

Metastaes are uncommon but may result from gastric cancer (Krukenberg tumor), colon cancer, pancreatic cancer, and melanoma. Metastases are often bilateral.