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Variety of supernumerary kidneys with one ureter, from Campbell's

Variety of supernumerary kidneys with two ureters, from Campbell's

Variety of crossed ectopia, from Campbell's

Variety of cross fused ectopia, from Campbell's

Malrotation: A embryonic, B normal, C incomplete, D hyper, E hyper, F reverse, from Campbell's

Retrocaval ureter, from Campbell's

Abnormal renal number

• Bilateral renal agenesis: rare (500 cases) and almost always incomplatible with life
• Unilateral renal agenesis: ureter absent in 60%, GU anomalies in 25-50% women (10-15% men), 50% men have absence of vas deferens, can perform VCUG (28% contralateral reflux), no sports restrictions, recommend BP and microalbuminuria checks 1-2x yearly to screen for renal disease, women should have pelvic US to screen for Mullerian abnormalities
• Supernumerary kidney: rare, incidentally diagnosed, usually asymptomatic

Renal dysplasia

• Renal dysgenesis: main cause of pediatric ESRD, renal US shows small, hyperechogenic kidneys, loss of corticomedullary and parenchymal/perirenal fat distinction, may have cysts
• Hypoplasia: decreased number of calyces and nephrons
• Oligomeganephronia: decreased number of nephrons but hypertrophy of each nephron
• Ask-Upmark kidney: acquired reflux nephropathy leads to segmental renal hypoplasia, patients have severe HTN, imaging shows slit scars on kidney, nephrectomy may treat unilateral disease

Renal ascent and fusion anomalies

• Simple ectopia: usually demonstrates incomplete rotation, hydronephrosis common, may be more likely to form stones and higher risk for trauma due to lack of protection, can be found pelvic or thoracic
• Crossed ectopia: 90% are fused to contralateral kidney, ureteral orifice usually orthotopic (ectopic UO 3%), VUR seen in 20% (71% if bilateral crossed ectopia), stone pain lateralizes to origin, pyelonephritis lateralizes to current location
• Horseshoe kidney: 95% fused at lower pole, pelves usually anterior, IMA usually blocks full ascent, isthmus usually parenchymal, ~13% develop pyelo and ~17% develop stones
• Malrotation: more common in Turner syndrome, may develop hydronephrosis

Vascular anomalies

• Accessory vessels: 15-29% have accessory artery, lower pole is most likely to have accessory vessel, occasionally cause UPJO
• Renal artery aneurysm: usually asymptomatic (especially in children), may present with pulsatile abdominal mass or bruit, 18% rupture risk if > 3cm, treat if > 3cm or > 2cm and asymptomatic
• Arteriovenous fistula: can be acquired (trauma, biopsy, surgery), may be secondary to aneurysm eroding into vein, can cause renal ischemia and hypertension, treat with embolization or surgery once diagnosed
• Retrocaval ureter (preureteral cava): right ureter crosses behind vena cava, due to failure of subcardinal vein to atrophy during development, contrast studies (CTU/MRU/RGPG) help delineate ureteral path, treated with ureteral division and reanastomosis (may need to resect aperistaltic segment)

Ureteral duplication

• Common, seen in 0.8% people
• Weigert Meyer rule: lower pole refluxes (VUR/UPJO), upper pole obstructs (ectopic/ureterocele)
• Ureteral triplication/quadruplication are very rare
• Bifid pelvis: seen in 10% patients (normal variant)