Correct Answer: C. Pelviureteric junction obstruction
Pelviureteric junction (PUJ) obstruction is characterized by a delayed intravenous urogram (IVU) showing a dilated renal pelvis with a normal-caliber ureter. The key discriminating finding is the "clubbing" or blunting of the calyces with a massively dilated pelvis, but the ureter remains normal in caliber distally—this is pathognomonic for PUJ obstruction. The delay in contrast excretion occurs because urine cannot drain efficiently from the pelvis into the ureter, causing backup and hydronephrosis. On delayed films, the contrast pools in the dilated pelvis, creating the characteristic appearance. PUJ obstruction is the most common cause of hydronephrosis in children in India (congenital narrowing at the PUJ) and can present in adults with flank pain, recurrent UTIs, or as an incidental finding. The obstruction may be intrinsic (stricture, kink, aberrant vessels) or extrinsic (crossing vessel). The normal ureter below the obstruction is the key finding that excludes other diagnoses. Management depends on symptoms and renal function; Anderson-Hynes pyeloplasty is the gold standard surgical treatment.
Why the other options are wrong
A. Staghorn calculus — Staghorn calculus would show a radiopaque branching calcification filling the renal pelvis and calyces on plain radiography and IVU. The delayed IVU would show non-functioning or poorly functioning kidney with the stone visible as a filling defect. Unlike PUJ obstruction, there is no normal-caliber ureter below the obstruction, and the calculus itself would be visible. Staghorn calculi cause obstruction at the level of the calyces/pelvis, not at the PUJ. B. Putty kidney — Putty kidney (xanthogranulomatous pyelonephritis) presents with a non-functioning or poorly functioning kidney on IVU, often with a history of recurrent infections and staghorn calculi. The kidney is typically shrunken and fibrotic, not dilated. The delayed IVU shows absent or minimal contrast excretion, whereas PUJ obstruction shows delayed but eventually good contrast pooling in a dilated pelvis. Putty kidney is a chronic inflammatory condition, not an obstructive lesion. D. Cystic kidney — Cystic kidney (autosomal dominant polycystic kidney disease or ADPKD) would show multiple bilateral cysts of varying sizes on IVU, with a characteristic 'Swiss cheese' appearance. The renal outline is enlarged and irregular. Unlike PUJ obstruction, there is no dilated pelvis with normal ureter; instead, the cysts compress and distort the collecting system. ADPKD typically presents with bilateral renal involvement and hypertension, not unilateral obstruction.
High-Yield Facts
- Delayed IVU in PUJ obstruction: dilated renal pelvis with normal-caliber ureter below the obstruction site—this is the pathognomonic finding.
- Most common cause of hydronephrosis in Indian children: congenital PUJ obstruction (intrinsic narrowing); presents with flank pain, UTI, or incidental finding.
- Anderson-Hynes pyeloplasty: gold standard surgical treatment for symptomatic or functionally significant PUJ obstruction (>40% split renal function).
- Differential on IVU: staghorn calculus shows radiopaque stone; putty kidney shows non-functioning kidney; cystic kidney shows bilateral cysts—none show the dilated pelvis + normal ureter pattern.
- Crossing vessel syndrome: extrinsic PUJ obstruction caused by aberrant renal artery or vein; accounts for ~15% of PUJ obstructions in adults.
Mnemonics
PUJ vs Other Obstructions (DILATE) Dilated pelvis, Intact ureter, Late contrast pooling, Anterior/posterior calyceal blunting, Typically unilateral, Excretion eventually normal = PUJ obstruction. Use this to quickly rule out staghorn (stone visible), putty kidney (non-functioning), and cystic kidney (bilateral cysts). PUJ Obstruction Memory Hook 'Pelvis Puffs, Ureter Stays Slim' — the pelvis dilates due to obstruction at the PUJ, but the ureter below remains normal-caliber. This single finding on delayed IVU is diagnostic.
NBE Trap
NBE may pair PUJ obstruction with staghorn calculus to trap students who confuse obstruction level (PUJ vs. calyceal/pelvic) or who focus on hydronephrosis alone without noting the normal ureter that excludes calculus and cystic disease. The delayed IVU appearance is the discriminator.
Clinical Pearl
In Indian clinical practice, congenital PUJ obstruction is the leading cause of antenatal hydronephrosis detected on prenatal ultrasound; many present later with recurrent UTIs or flank pain. A delayed IVU showing the 'clubbed' dilated pelvis with normal ureter is the bedside clue that pyeloplasty, not nephrectomy, is the answer—preserving renal function is key in a young patient.
_Reference: Bailey & Love Ch. 76 (Urology); Harrison Ch. 279 (Obstructive Uropathy)_