4.1 Renal system Flashcards
Renal Embryology
Kidneys form from pro-, meso- and metanephros; first two regress and only latter persists
Ureteric bud from outgrowth of mesonephric duct
Form in sacrum and migrate caudally by 8 weeks gestation; maturation continues to 5 y/o
US Renal cortex and medulla
Renal medulla hypoechoic to cortex
Renal Mass CT protocol
Noncontrast Corticomedullary phase (25-30 seconds) Nephrographic phase (80 seconds)
Horseshoe kidney - formation, risks
Abnormal axis - lower calyx more medial than upper
Bilateral malrotation with pelvises in anterior position
Isthmus fibrous or parenchymal, between IMA and aorta
Obstruction, infection, calculus formation in 30%, particularly PUJ
Increased risk with trauma and malignancies including Wilms tumour
Association with Cardiovascular, MSK, anorectal anomalies
Septum of Bertin - location, association
90% upper pole, 60% bilateral
Associated with bifid renal pelvis
Congenital megacalyces - definition, consequences
Excess of enlarged calyces (20-25 vs normal 10-14), causing hypoplastic pyramids
No obstruction, normal renal parenchyma and function
Pyelocalcyceal Diverticulum - definition, types
Outpouching of calyx into corticomedullary region; usually asymptomatic but may cause calculi
Type 1: from minor calyx
Type 2: from infundibulum
Type 3: from renal pelvis
ADPKD - definition, prevalance, association, criteria
Cystic dilatation of collecting tubules and nephrons; 0.1% population, 10% dialysis patients, strong penetrance
Hepatic cysts (70%), intracranial berry aneurysms (20%), pancreatic and splenic cysts less than 5%
Presents with flank pain and haematuria, can get cyst calcification and haemorrhage
Criteria: 2 or more cysts bilaterally on US in at risk patient at less than 30 y/o or any pt 30-60 y/o, or 4 or more cysts bilaterally if > 60 y/o
Acquired cystic kidney disease - definition
Multiple renal cysts developed in CRF; occur in 90% patients on dialysis
3-5 cysts in each kidney, CRF and no history of inherited cystic disease
Hemorrhagic cysts occur in 50%, can rupture
RCC develops in 7%
Bosniak criteria
- Benign simple cyst, don’t communicate with collecting system
- Minimally complicated, benign but with concerning features
Thin septations (less than 1 mm)
Fine calcifications
Hyperattenuating (>20)
2F. Multiple septa with or without perceptible but not measurable enhancement; can have thick or nodular calcification, also included if hyperattenuating and >3 cm - Complicated, multiloculated but with malignant features.
- Clearly malignant with large cystic component
Miscellaneous cysts
Milk of calcium: calcium carbonate granules, not true cyst but calyceal diverticulum
Parapelvic: originates in renal parenchyma but expands into renal sinus
Peripelvic: from sinus structures, likely lymphatic, may look like hydronephrosis on US
Perinephric: not true cyst, are extravasated urine trapped beneath capsule (urinoma)
Medullary cystic disease - cause
Due to tubulointerstitial fibrosis
Presents with anaemia and renal failure
Small kidneys with multiple small medullary cysts, often merely causes medullary increased echogenicity, thinned cortex
Types of medullary cystic disease
Familial nephronophthisis (70%): AR, juvenile onset at 3-5 years but also adult type
Adult medullary cystic disease (15%): AD inheritance
Renal retinal dysplasia (15%): recessive, associated with retinitis pigmentosa
Causes of Nephrocalcinosis
Metastatic (normal kidneys), dystrophic (injured tissue) or urine stasis
Hyperparathyroidism (primary and secondary)
Metastatic carcinoma to bone and hypercalcaemia of malignancy
Prolonged immobilisation
Sarcoidosis
Milk alkali syndrome
Hypervitaminosis D
RTA (often dense medullary calcification)
Medullary sponge kidney (urine stasis)
Hyperoxaluria
Bartter’s syndrome
Prolonged frusemide (usually premature infants)
Nephrotoxic drugs
Papillary necrosis
Medullary sponge kidney - AKA, associations, IVP
AKA Benign renal tubular ectasia, Cacchi-Ricci disease
Dysplastic cystic dilatation of papillary / medullary portions of collecting ducts, usually 20-40 y/o
75% bilateral, often asymptomatic; 10% develop progressive renal failure
IVP - striated nephrogram (brushlike), ‘bunch of flowers’ appearance
Associations: Hemihypertrophy, Beckwith-Wiedemann, Pyloric stenosis, Ehlers Danlos, RTA, any form of renal cystic disease / ectopia
Renal cell carcinoma - presentation, association
Haematuria, pain, mass, weight loss
Paraneoplastic: HTN - renin, erythrocytosis - EPO, hypercalcaemia - PTH, gynaecomastia - gonadotropin, Cushing - ACTH.
Associations: tobacco, vHL (bilateral), TS, dialysis, family history, petroleum, acquired cystic renal disease
Usually recurs at less than 2 years, but can have late recurrence - 10% recur 10 years after nephrectomy
RCC Types and imaging
Clear cell (65%) - proximal tubule
Papillary (15%) - chromophil, proximal tubule
Chromophobe (10%) - intercalated cell of cortical collecting duct
Oncocytoma (5%)
Unclassified (5%)
Best evaluated in nephrographic phase, venous invasion best characterised by MRI
US: 70% hyperechoic if > 3 cm, 30% if less than 3 cm
95% hypervascular, 10-30% calcified
Oncocytoma - origin, CT
From epithelial cells of proximal tubule, usually well-differentiated and benign but need resection
Central stellate scar (25-33% on CT) and spoke wheel (angiography), usually homogeneous enhancement, can’t differentiate from RCC on imaging, but FNA can discriminate
Juxtaglomerular tumour - associations
Rare. Secrete renin, cause HTN, hypernatraemia, hypokalaemia
Staging RCC
I: kidney only
II: extrarenal ± adrenal involvement, but confined within Gerota’s fascia
III: A - renal vein, B - lymph node metastases, C - both
IV: A - direct extension to other organs through Gerota’s fascia; B - metastases (lung (55%) > liver > bone > adrenal > contralateral kidney (10%))
Renal lymphoma - type, frequency, patterns, MR
Occurs in 8% lymphoma patients, 75% bilateral, NHL > HL.
Characteristically, renal vessels remain patent despite encasement
MR: hypointense to cortex on T1W, heterogeneously hypo to isointense on T2W
Patterns (five):
Mulitple renal masses (59%)
Solitary mass (3%)
Renal invasion (contiguous RP spread)
Perirenal (10%)
Diffuse renal infiltration (rare)
Renal metastases - types
Fifth most common metastatic site, mainly haematogenous spread
Lung, breast and contralateral kidney
Colonic metastases often solitary and exophytic
Melanoma metastases often have perinephric extension
Angiomyolipoma - CFs, associations, Rx
Benign hamartomas - blood vessels, smooth muscle, fat; DO NOT contain calcification
Can cause pain, haematuria, anaemia
Usually multiple in tuberous sclerosis (80% of TS have AML)
Sporadic form commonest (80-90%): F/M = 4/1, usually middle aged; thus less than 40% of patients with AML have TS
At least annual follow-up if approaching 4 cm due to risk of haemorrhage, lesions > 4 cm often resected / ablated.
Intratumoural fat almost diagnostic (CT or chemical shift), 5% do not contain fat
May extend into renal vein and IVC
Tuberous sclerosis - inheritance, CFs
AD, variable penetrance; >50% sporadic
Epilepsy, mental retardation and adenoma sebaceum
Also subependymal nodules, giant cell astrocytoma, peripheral tubers, retinal hamartomas, cardiac rhabdomyomas, lymphangioleiomyomatosis, shagreen patches, subungual fibromas, bone cysts
50% have renal lesions
Bilateral renal cysts
Multiple AMLs are sine qua non of TS (15% patients)
RCC (1-2%)
Renal adenoma - definition, Rx
Solid lesion less than 3 cm
Now considered renal carcinoma (adenocarcinoma) in evolution and treated with partial nephrectomy
Renal Pelvis Tumours - Types, imaging
Tend to maintain reniform outline of kidney
Inverted Papilloma (No malignant potential, 20% risk of associated urothelial malignancy)
TCC
SCC (5% renal pelvis tumours, less than 1% all renal tumours)
Collecting Duct Carcinoma (rare, aggressive, possible from distal collecting ducts of Bellini, often infiltrative rather than expansile)
TCC of Upper Renal Tract - associations, CT, IVP
Often multifocal; 40-80% have bladder TCC but only 3% bladder TCC later develop upper renal tract TCC
10% of upper renal tract neoplasms, 2-4% bilateral, 2-7% calcification
Hyperechoic on US and hyperattenuating on CT
Causes faceless kidney - obliteration of sinus fat and infiltration of parenchyma
Stippling sign on IVP - tracking of contrast interstitially in papillary lesion
Stricturing - thus can mimic renal TB
60% ipsilateral recurrence and 50% have lung metastases
Staging of TCC of upper tract
Stage I and II: limited to lamina propria / muscular layer, III: renal parenchyma / adjacent fat, IV: metastatic (usually liver, lung, bones)
Indications for partial nephrectomy
Solitary RCC less than 7 cm confined to kidney
RCC in solitary kidney
Significant risk of later CRF
Von Hippel Lindau - inheritance, associations, CFs
AD, almost 100% penetrance
Usually renal cysts
25-40% develop clear cell RCC (often 30-40 y/o), often synchronous / metachronous; often screen from 20’s.
Also have pancreatic cysts (30%), islet cell tumours, phaeochromocytomas (10%, often multiple and ectopic, 50-80% bilateral), retinal angiomas, ANS haemangioblastomas
More rarely endolymphatic sac tumours, cystadenomas of epididymis, broad ligament cysts
GU Tuberculosis - CFs, imaging
Second most common site of TB, usually haematogenous spread, may be asymptomatic
Active / healed pulmonary TB in 50%
50% calcification (amorphous granular if active, dense punctate if healed tuberculomas - putty kidney)
Usually bilateral asymmetrical involvement, 25% unilateral
Tubercles become cavities, communicating with calyces, which then stricture, can cause autonephrectomy
Can cause epididymitis, hydrocoele, testicular mass, prostatitis, female infertility
Kidneys: Smudged papillae, moth-eaten calyx, ‘hiked-up’ pelvis - cephalad retraction of infero-medial margin of pelvis at PUJ
Ureters: Usually unilateral, beaded corkscrew appearance (alternating scarring & dilatation), aperistaltic and shortened (pipestem)
Bladder: Chronic interstitial cystitis causing fibrosis; Small, trabeculated, VU reflux, wall rarely calcified
Prostate: Dense calcification
Acute Pyelonephritis - types, CT/IVP, complications
Focal - lobar nephronia, Diffuse.
IVU / CT non-specific - renal enlargement and loss of corticomedullary differentiation, striated nephrogram, delayed enhancement and excretion
Hydroureternephrosis can occur due to bacterial endotoxin
Can progress to abscess (usually gram negative but can be staph or candida, 30 HU attenuation, rounded margins and enhancing walls, ± perinephric stranding)
Pyonephrosis - due to obstruction (calculi > tumour > postoperative strictures) - US can differentiate from hydronephrosis, usually requires nephrostomy / stenting in acute phase.
Emphysematous pyelonephritis - RFs, types
Usually diabetic & E Coli (gas forming gram negatives) infection, occasionally non-DM with obstruction Best diagnosed on CT, often requires nephrectomy if severe Type 1 (pyelonephritis): Destruction > one third renal parenchyma, 70% mortality, gas in parenchyma Type 2 (pyelitis): Destruction less than one third parenchyma, 20% mortality, renal/perirenal collection with gas in collecting system
Xanthogranulomatous pyelonephritis - definition, imaging, types
Replacement of renal parenchyma by lipid laden macrophages, begins in pelvis and extends to cortex and medulla
Multiple low attenuation (-10 to 30 HU) xanthomatous masses (may show fine calcifications, thin rim of peripheral enhancement) ± thickened Gerota’s fascia ± psoas abscess
Chronic indolent bacterial infection, usually E Coli or Proteus; 10% diabetic, typically middle aged females
90% diffuse, 10% focal
Absent / decreased contrast excretion on affected side
75% due to staghorn calculus; 25% due to PUJ obstruction or tumour
May lead to replacement lipomatosis (severe parenchymal atrophy)
Renal papillary necrosis - definition, imaging
Ischaemic coagulative necrosis of pyramids / medullary papillae; chronic tubulointerstitial nephropathy; predominantly affects medulla
Gradual development of cleft in papilla ± sloughing ± rimlike calcification
‘Lobster claw’ initially, then ‘ring sign’ around sequestered sloughed papilla, ultimately calyceal blunting after necrosis and absorption
Causes of renal papillary necrosis
(due to ischaemic and/or infective necrosis) DM Analgesia Sickle cell Pyelonephritis Renal vein thrombosis Tuberculosis Obstructive uropathy
Renal Trauma Categories / Grading
80% blunt trauma, 20% penetrating
Absence of haematuria does not preclude serious renal injury
I (75-85%): Contusions, small lacerations with no communication with collecting system (includes isolated subcapsular and perinephric haematomas, conservative management
II (10%): Laceration through cortex ± urine extravasation; may be managed conservatively
III (5%): Multiple deep lacerations with renal pedicle injury
IV (rare): PUJ avulsion / laceration of renal pelvis
Imaging findings of renal injury
Evaluated at CECT at 70 seconds and 3 minutes
Contusion: Swelling, irregular high-density infiltrate on NECT, ovoid low attenuation areas on CECT
Laceration: superficial - limited to cortex, deep - extends to medulla, ± contrast extravasation to perinephric tissues
Infarction: Non-enhancing, peripheral, wedge shaped; due to thrombosis / laceration of segmental artery
Acute renal vein occlusion: Enlarged kidney, ± thrombus in renal vein, venography may be required
PUJ injuries: rare, medial perinephric urine extravasation + circumrenal urinoma
Renal Haemorrhage - locations
Suburothelial - thickened wall of pelvis / proximal ureter due to blood
Subcapsular - recent blood is higher attenuation than parenchyma, kidney flattened with elevated capsule, eventually may calcify; if large and chronic may cause hypertension (Page kidney)
Perinephric - usually extends below renal margin
Renal infarction - causes, types
Due to RA thrombosis or embolism, vasculitis, trauma, sickle cell, aortic dissection
Types
Global: Non-enhancing kidney, high density capsular rim (collateral perfusion)
Large branch occlusion: Wedge shaped defect, base on capsule, apex towards hilum, ± cortical rim enhancement
Small vessel occlusion (emboli, vasculitis, sickle cell): Multiple, often bilateral infarcts, ‘slit-like’ in sickle cell, may show cortical rim enhancement (unlike pyelonephritis)
Renal Artery Occlusion may present with Severe flank pain, haematuria, albuminuria, leukocytosis, fever, tender renal mass; or may be asymptomatic
Renal vein thrombosis - imaging
Causes smooth, swollen kidney with variable contrast excretion (can be dense nephrogram) ± occluded collecting system
Can cause cortical rim sign; varices may indent pelvis / ureter
CT: prolonged corticomedullary differentiation, characteristic fine linear densities extending from kidney to perirenal space, enhance post contrast
US: Initially hypoechoic, then hyperechoic at 10 days due to cellular infiltrates / fibrosis; in late phase (several weeks) small hyperechoic kidney with loss of corticomedullary differentiation
If complete acute occlusion, can cause infarction
Causes of renal vein thrombosis
Malignant (extrinsic compression or direct extension)
Primary renal disease (membranous GN commonest, SLE, amyloid)
Secondary from IVC thrombosis
Infants: sickle cell, haemoconcentration (diarrhoea, sepsis), hypoxia in congenital heart disease, maternal diabetes
Acute Cortical Necrosis - definition, imaging
Pathological progression of ATN; Ischaemic cortical necrosis with medullary sparing; usually bilateral
Acute: unenhanced cortex between enhancing medulla and enhancing cortical rim
Chronic: small smooth kidneys, may show cortical calcification
Causes of acute cortical necrosis
(60% ischaemia, 40% nephrotoxins): Haemorrhage (classically 3rd trimester) Septic abortion Trauma with shock Severe dehydration Haemolytic uraemic syndrome Acute aortic dissection Transfusion reaction Toxins (including snake venom)
Renal artery stenosis - causes, imaging
Causes: atherosclerosis (90%; narrows ostium or proximal 2 cm of RA), FMD (mid-distal RA, ‘string of beads’)
Causes 1-5% HTN in young adults
CECT: Prolonged CMD implies significant stenosis
CEMRA: Highly sensitive in proximal RAS
Angiography: Gold standard, but can’t assess haemodynamic significance of lesion
US: Peak systolic velocity > 150 cm/s, acceleration time > 0.07 s (parvus et tardus waveform), post-stenotic spectral broadening / flow reversal
Collecting system obstruction - imaging, test
Due to calculi, tumour, surgery
Causes delayed nephrogram (>30 minutes on IVP), with faint radial striations
Negative pyelogram: nephrogram with delayed pyelogram (thus unopacified calyces outlined by parenchyma)
Dunbar’s crescents (calyceal crescent sign): thin rings at interface with calyx / parenchyma, due to contrast in dilated collecting ducts
Acute obstruction typically > 20 cm H2O (normal and chronic obstruction less than 15 cm H2O)
Whitaker test - pressure-flow study, measures bladder and collecting system (percutaneously) pressures
Causes of false positives in US assessment for hydronephrosis
Extrarenal pelvis, peripelvic cyst
Vesicoureteric reflux with full bladder
High urine flow (diuresis)
Prune belly syndrome
Common complications of renal transplant
ATN (normal flow, reduced excretion) - rarely occurs > 1 month post transplant
Rejection (Resistive index >0.7 ([systolic-diastolic]/systolic, nonspecific), 90% show increased size (but normally decreased if chronic); thickened cortex; large renal pyramids with indistinct CM junction, focal hypechoic areas in cortex / medulla (20%), increased cortical echogenicity (15%)); hyperacute rejection shows decreased flow but delayed excretion
Cyclosporine toxicity - similar pattern to ATN but later post-transplant, rare within first month
Arterial occlusion (87% success of angioplasty for anastomotic stenosis)
Venous occlusion (RVT normally occurs in first 3 days post transplant)
Urinary leak
Urinary obstruction
Causes of perirenal fluid collections post-transplant
Lymphocoele (10-20% at 1-4 months post transplant; usually inferomedial to kidney and linear septations present in 80%)
Abscess (usually develops within weeks)
Urinoma (develops in first month, generally near VUJ, may be cold on nuclear medicine if not active)
Haematoma
