4.1 Renal system

Question 1

Renal Embryology

Answer 1

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

Question 2

US Renal cortex and medulla

Answer 2

Renal medulla hypoechoic to cortex

Question 3

Renal Mass CT protocol

Answer 3

Noncontrast
Corticomedullary phase (25-30 seconds)
Nephrographic phase (80 seconds)

Question 4

Horseshoe kidney - formation, risks

Answer 4

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

Question 5

Septum of Bertin - location, association

Answer 5

90% upper pole, 60% bilateral

Associated with bifid renal pelvis

Question 6

Congenital megacalyces - definition, consequences

Answer 6

Excess of enlarged calyces (20-25 vs normal 10-14), causing hypoplastic pyramids
No obstruction, normal renal parenchyma and function

Question 7

Pyelocalcyceal Diverticulum - definition, types

Answer 7

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

Question 8

ADPKD - definition, prevalance, association, criteria

Answer 8

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

Question 9

Acquired cystic kidney disease - definition

Answer 9

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%

Question 10

Bosniak criteria

Answer 10

1. Benign simple cyst, don’t communicate with collecting system
2. 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
3. Complicated, multiloculated but with malignant features.
4. Clearly malignant with large cystic component

Question 11

Miscellaneous cysts

Answer 11

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)

Question 12

Medullary cystic disease - cause

Answer 12

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

Question 13

Types of medullary cystic disease

Answer 13

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

Question 14

Causes of Nephrocalcinosis

Answer 14

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

Question 15

Medullary sponge kidney - AKA, associations, IVP

Answer 15

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

Question 16

Renal cell carcinoma - presentation, association

Answer 16

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

Question 17

RCC Types and imaging

Answer 17

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

Question 18

Oncocytoma - origin, CT

Answer 18

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

Question 19

Juxtaglomerular tumour - associations

Answer 19

Rare. Secrete renin, cause HTN, hypernatraemia, hypokalaemia

Question 20

Staging RCC

Answer 20

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%))

Question 21

Renal lymphoma - type, frequency, patterns, MR

Answer 21

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)

Question 22

Renal metastases - types

Answer 22

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

Question 23

Angiomyolipoma - CFs, associations, Rx

Answer 23

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

Question 24

Tuberous sclerosis - inheritance, CFs

Answer 24

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%)

Question 25

Renal adenoma - definition, Rx

Answer 25

Solid lesion less than 3 cm | Now considered renal carcinoma (adenocarcinoma) in evolution and treated with partial nephrectomy

Question 26

Renal Pelvis Tumours - Types, imaging

Answer 26

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)

Question 27

TCC of Upper Renal Tract - associations, CT, IVP

Answer 27

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

Question 28

Staging of TCC of upper tract

Answer 28

Stage I and II: limited to lamina propria / muscular layer, III: renal parenchyma / adjacent fat, IV: metastatic (usually liver, lung, bones)

Question 29

Indications for partial nephrectomy

Answer 29

Solitary RCC less than 7 cm confined to kidney RCC in solitary kidney Significant risk of later CRF

Question 30

Von Hippel Lindau - inheritance, associations, CFs

Answer 30

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

Question 31

GU Tuberculosis - CFs, imaging

Answer 31

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

Question 32

Acute Pyelonephritis - types, CT/IVP, complications

Answer 32

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.

Question 33

Emphysematous pyelonephritis - RFs, types

Answer 33

``` 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 ```

Question 34

Xanthogranulomatous pyelonephritis - definition, imaging, types

Answer 34

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)

Question 35

Renal papillary necrosis - definition, imaging

Answer 35

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

Question 36

Causes of renal papillary necrosis

Answer 36

``` (due to ischaemic and/or infective necrosis) DM Analgesia Sickle cell Pyelonephritis Renal vein thrombosis Tuberculosis Obstructive uropathy ```

Question 37

Renal Trauma Categories / Grading

Answer 37

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

Question 38

Imaging findings of renal injury

Answer 38

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

Question 39

Renal Haemorrhage - locations

Answer 39

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

Question 40

Renal infarction - causes, types

Answer 40

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

Question 41

Renal vein thrombosis - imaging

Answer 41

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

Question 42

Causes of renal vein thrombosis

Answer 42

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

Question 43

Acute Cortical Necrosis - definition, imaging

Answer 43

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

Question 44

Causes of acute cortical necrosis

Answer 44

``` (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) ```

Question 45

Renal artery stenosis - causes, imaging

Answer 45

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

Question 46

Collecting system obstruction - imaging, test

Answer 46

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

Question 47

Causes of false positives in US assessment for hydronephrosis

Answer 47

Extrarenal pelvis, peripelvic cyst Vesicoureteric reflux with full bladder High urine flow (diuresis) Prune belly syndrome

Question 48

Common complications of renal transplant

Answer 48

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

Question 49

Causes of perirenal fluid collections post-transplant

Answer 49

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