Paper II
Question
Obstructive uropathy
Answer
Obstructive uropathy refers to structural or functional obstruction anywhere along the urinary tract, leading to dilatation of the urinary system proximal to the block (hydronephrosis, hydroureter) and progressive renal damage.
Causes:
- Congenital: Posterior urethral valves, ureteropelvic junction obstruction, urethral strictures.
- Acquired: Calculi (most common), benign prostatic hyperplasia, prostate/bladder/cervical carcinoma, retroperitoneal fibrosis, pregnancy, neurogenic bladder, blood clots, papillary necrosis.
Pathogenesis:
- Obstruction raises intraluminal pressure proximal to the block, which is transmitted back to the renal pelvis and calyces, and eventually to the nephrons.
- Initially, there is a transient rise in glomerular filtration pressure and renal blood flow (compensatory), followed by a progressive fall in GFR and renal blood flow as vasoconstrictive mediators (e.g., angiotensin II, thromboxane A2) are activated.
- Sustained increased pressure causes atrophy of the renal parenchyma, tubular damage, and interstitial fibrosis, ultimately progressing to chronic kidney disease if unrelieved.
Morphology:
- Hydronephrosis: Dilated renal pelvis and calyces; with time, progressive cortical and medullary thinning/atrophy due to pressure atrophy.
- Complete obstruction leads to more diffuse and severe glomerular/cortical damage than incomplete obstruction, which mainly damages the medulla first (tubular concentrating defect appears early — impaired urinary concentrating ability).
- Superimposed infection (pyelonephritis) is common and worsens damage.
Clinical features: Depend on level and completeness of obstruction — may range from asymptomatic to flank pain, renal colic (with calculi), urinary retention, recurrent UTIs, and eventually renal failure if bilateral or unrelieved. Removal of the obstruction can allow significant, though sometimes incomplete, recovery of renal function.