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PA27.12-13 | Cystic Kidney Disease, Renal Stones & Obstructive Uropathy — SDL Guide (Part 3)

Hydronephrosis — Morphology and Grades

Morphological Grades of Hydronephrosis

Morphological appearance:

Gross: The renal pelvis and calyces are progressively dilated. In early obstruction, only the pelvis is dilated (pelvicaliectasis). In advanced disease, the kidney is converted into a large, thin-walled sac of fluid — the cortex is reduced to a thin rim.

Cut section shows:
- Dilation of calyces → blunting of papillae → progressive papillary atrophy.
- Cortical thinning (normal cortex ~10–12 mm; advanced hydronephrosis may reduce this to 1–2 mm).
- In complete obstruction, the parenchyma is entirely replaced by fibrous tissue and fluid.

Microscopy: Tubular dilation → tubular atrophy → interstitial fibrosis → glomeruli initially spared then globally sclerosed in late stages.

Progression and Complications of Hydronephrosis

Complications of obstructive uropathy:
1. Urinary tract infection → pyelonephritis — stasis promotes bacterial growth; if infected → pyonephrosis (pus-filled hydronephrotic kidney) — surgical emergency.
2. Stone formation — stasis promotes nucleation and crystallisation.
3. AKI — bilateral obstruction or obstruction in a solitary functioning kidney.
4. CKD — chronic partial obstruction is a silent cause of progressive renal impairment.
5. Hypertension — activation of the renin–angiotensin system.
6. Post-obstructive diuresis — after relief of bilateral obstruction, massive salt and water diuresis; requires careful fluid and electrolyte replacement.

Distinguishing ADPKD from Other Cystic Diseases — A Framework

Examiners frequently ask you to distinguish ADPKD from ARPKD and from acquired cystic disease. Use this framework:

Feature	ADPKD	ARPKD	Acquired Cystic Disease
Inheritance	Autosomal dominant	Autosomal recessive	Acquired (dialysis)
Gene	PKD1/PKD2	PKHD1	Somatic
Age of onset	4th–5th decade	Perinatal / infantile	After 5–10 yrs dialysis
Cyst distribution	Bilateral, all segments	Bilateral, collecting ducts	Bilateral, cortex/medulla
Cyst size	Large, varied (mm–cm)	Tiny, radial sponge	Small–medium
Associated lesion	Berry aneurysm, hepatic cysts, MVP	Congenital hepatic fibrosis	↑ RCC risk
ESRD timing	5th–6th decade	Childhood (severe forms)	Already in ESRD
Key clinical pointer	Family history, palpable kidneys, hypertension, SAH	Neonate / infant, Potter sequence, portal hypertension	Long-term haemodialysis patient

Simple cortical cysts differ from all of the above: unilateral or few bilateral, large, unilocular, in adults over 50, no genetic basis, no ESRD risk.