GU Flashcards
What separates the three components of the retroperitoneum?
Separated by the anterior and posterior renal fascia and lateral conal fascia
What are the three compartments of the retropertoneum?
Anterior pararenal space
Perirenal space - surrounds each kidney
Posterior pararenal space
What is in the anterior pararenal space?
Ascending colon
Descending colon
(2nd and 3rd) duodenum
Pancreas
What is in the perirenal space?
Surrounds each kidney
Kidneys
Proximal ureter
Adrenals
Lots of fat
What is in the posterior pararenal space?
Potential space, contains only fat
May become secondarily involved in inflammatory processes
Clinically important as a pathway for potential disease spread due to secondary involvement of inflammation or neoplasm.
MC primary retroperitoneal retroperiteonal tumor?
Liposarcoma
What is retroperitoneal fibrosis?
Rare inflammatory disorder causing increased fibrotic deposition in the retroperitoneum, often leading to ureteral obstruction.
Unlike malignant retroperiteonal adenopathy, retroperitoneal fibrosis tends not to elevate the aorta off the spine.
What are the two components of the adrenal glands and what are they derived from?
The cortex is derived from mesothelium
The medulla is derived from neural crest
What does the adrenal cortex make?
Synthesizes the steroid hormones aldosterone, glucocorticoids, and androgens, which are all biochemical derivatives of cholesterol.
What are the three layers of the adrenal cortex and what do they make?
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.
What pathology can affect the adrenal cortex?
Adrenal hyperplasia
Adrenal adenoma
Adrenal cortical carcinoma
What does the adrenal medulla make?
Central portion of the adrenal gland and produces the catecholamines norepinephrine and epinephrine, which are derived from tyrosine.
What pathology can affect the adrenal medulla?
Pathology of the adrenal medulla includes pheochromocytoma and the neuroblastic tumors (ganglioneuroma, ganglioneuroblastoma, and neuroblastoma).
Conditions associated with adrenal hyperfunction?
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.
Adrenal cortical carcinoma is a very rare adrenal malignancy that arises from the cortex and typically causes a disordered increase in all cortical adrenal hormones and precursors.
Pheochromocytoma is a usually benign tumor of the adrenal medulla that causes an increase in catecholamines.
What is Waterhouse–Friderichsen syndrome?
Post-hemorrhagic adrenal failure secondary to Neisseria Meningitidis bacteremia.
Idiopathic adrenal hemorrhage is usually unilateral and rarely causes adrenal hypofunction.
What percentage of adrenal adenomas are lipid-rich (<10 HU)?
80%
What is a collision tumor?
Metastasis into an adrenal gland with a pre-existing adenoma
“Adenoma” appears heterogeneous or has shown an interval increase in size, then a collision tumor should be considered in a patietn with known primary even if region attenuates <10 HU.
Why do adrenal adenomas contain fat?
Intracytoplasmic lipid due to steroid production.
What malignancies also contain intracytoplasmic lipid and would also lose signal on out-of-phase images similar to an adenoma?
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).
How do adenomas washout compared to metastases?
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
What is the adrenal washout formula?
%washout = (enhanced attenuation - delayed attenuation) / (enhanced attenuation - unenhanced attenuation)
> 60% absolute washout is diagnostic of adenoma
What is adrenal relative washout?
If unenhanced CT is not available or not performed due to concern for radiation
exposure
% relative washout = (enhanced attenuation - delayed attenuation) / (enhanced attenuation)
> 40% relative washout is diagnostic of adenoma
What % washout is diagnostic of adenoma on absolute and relative?
Absolute >60%
Relative >40%
In patient with known primary what is a lesion that does not demonstrate benign washout kinetics?
Suspicious for, but not diagnostic of, metastasis.
What is an adrenal myelolipoma?
Benign neoplasm consisting of myeloid cells (i.e., erythrocyte precursors) and fat cells.
What is a Pheochromocytoma?
Pheocytoma is a neoplasm of chromaffin cells, usually arising from the adrenal medulla. Pheochromocytoma may cause hypertension and episodic headaches/ diaphoresis.
What is the “rule of 10s” with pheochromocytomas?
10% are extra-adrenal.
10% are bilateral.
10% are malignant.
10% are familial or syndromic.
What syndromes are Pheochromocytomas associated with?
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).
What is an extra-adrenal pheochromocytoma called?
Paraganglioma
Locations of paragangliomas (extra-adrenal pheochromocytomas)?
The most common intraabdominal location of a paraganglioma 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 syncope (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).
MC cancers to cause adrenal metastases?
Lung and melanoma
What causes adrenal calcification?
Wegener granulomatosis
TB
Hisoplasmosis
Old hemorrhage
What is Gerota’s Fascia?
Anterior renal fascia - separates the anterior pararenal and perirenal space.
What is Zuckerkandl’s Fascia?
Posterior renal fascia - separates the perirenal fascia and the posterior renal fascia
What is a renal mass protocol multiphase CT?
Unenhanced, nephrographic (100 second delay), and pyelographic (excretory phase - 15 min delay) phases.
Timing of the nephrographic phase?
100 second delay
Timing of the pyelographic/excretory phase?
15 minute delay
What is the most important characteristic to distinguish between a benign and malignant non-fat-containing renal mass?
Enhancement
A lesion containing intralesional fat is almost always a benign AML, even if it enhances.
What is considered enhancement in CT?
Quantified as the absolute increase in HU on post-contrast images, compared to pre-contrast:
<10 HU: no enhancement
10-19: equivocal enhancement
>20 HU: enhancement
What is considered enhancement in MRI?
Quantified as percent increase in signal intensity as measured on postcontrast images:
<15%: no enhancement
15-19%: equivocal enhancement
>20% enhancement
When is a lesion “too small to characterize”?
If the lesion diameter is smaller than twice the slice thickness.
Ex, 3 mm slices, a lesion less than 6 mm cannot be accurately characterized based on attenuation or enhancement.
What do RCCs arise from?
Renal tubular cells
Risk factors for development of RCC
Smoking, acquired cystic kidney disease, VHL, and tuberous sclerosis
What are the subtypes of RCC?
Clear cell - MC Papillary Chromophobe Collecting duct carcinoma Medullary carcinoma
What is the MC subtype of RCC?
Clear cell
Enhances more avidly than the less common subtypes.
Can be sporadic or associated with VHL
Characteristics of clear cell RCC?
Enhances more avidly than the less common subtypes.
Can be sporadic or associated with VHL
What subtype of RCC is associated with VHL?
Clear Cell
Characteristics of Papillary RCC?
Hypovascular subtype- 80-90% 5-year survivial
Enhances only mildly due to its hypovascularity.
A renal “adenoma” is frequently seen on autopsy specimens and is a papillary carcinoma <5 mm.
Hypovascular subtype of RCC?
Papillary RCC
What is the Chromophobe subtype of RCC?
Best prognosis - 90% 5 year survival.
Subtype of RCC with best prognosis?
Chromophobe - 90% 5-year survival.
What is Medullary Carcinoma RCC?
Rare, but known to affect mostly young adult males with sickle cell trait.
Extremely aggressive neoplasm with mean survival of 15 months, not helped by chemotherapy.
Subtype of RCC associated with sickle cell trait?
Medullary Carcinoma RCC.
Staging of RCC
Robson System - characterizes fascial extension and vascular/lymph node involvement. I-III are resectable.
Stage I: tumor confined to w/in the renal capsule
Stage II: Tumor extends out of the renal capsule but remains confined with Gerota’s fascia.
Stage III: Vascular and/or LN involvement
A: RV involvement or IVC involvement.
B: LN involvement
C: Venous and LN involvement
Stage IVA: Tumor growth through Gerota’s Fascia
Stage IVB: Distant metastasis
MC benign renal neoplasm?
AML
Characteristics of AML in fat saturation vs in an out of phase imaging?
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 signal drop-out on dual-phase MRI.
Small hyperdense enhancing mass does not contain macroscopic fat - what to do next?
MRI - T2-weighted images to distinguish from RCC
T2 hyperintense mass suggests RCC (clear cell subtype) - surgery
T2 hypointense mass is nonspecific and can represent either RCC (papillary type) or AML with minimal fat. Although AML would enhance avidly than a papillary RCC, biopsy is warranted for definitive diagnosis.
What is an Oncocytoma?
Most commonly resected benign renal mass and has overlapping imaging findings with RCC.
Can suggest oncocytoma on imaging, but imaging features are not specific and cannot be reliably differentiated from RCC.
Imaging features suggestive of oncocytoma are homogeneous enhancement and a central scar.
Oncocytic cells can sometimes be found in the rare chromophobe RCC subtype- can distinguish between clear and papillary RCC.
What imaging findings can suggest oncocytoma?
Homogeneous enhancement and a central scar.
Patterns of renal involvement of lymphoma
Primary renal lymphoma is rare - no native lymphoid tissue. May become involved from hematogenously disseminated disease or spread from the retroperitoneum.
Multiple lymphomatous masses (MC pattern - 50%)
Solitary renal mass
Diffuse lymphomatous infiltration, causing nephromegaly
Direct extension of retroperitoneal disease
What are non-neoplastic solid renal masses?
Infection- especially focal pyelonephritis. Renal abscess may be difficult to differentiate on imaging from a cystic RCC.
Renal AVM- will avidly enhance and mimic a hypervascular renal mass. Clue: asymmetric enhancement of the renal vein on the affected side, due to early shunting of venous blood.
What are the renal pseudotumors?
Normal variations of renal morphology that may mimic a renal mass.
Hypertrophied column of Bertin
Persistent fetal lobation/lobulation
What are the columns 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.
What are persistent fetal lobation/lobulation?
In normal fetal development- the fetal kidneys are divided into discrete lobes. Occasionally, can persist in adulthood, producing an indentation of the renal cortex. This indentation can cause an adjacent focal bulge that stimulates a renal mass. Can usually be distinguished from a true mass by the presence of septa of Bertin on either side.