Cystic Diseases of the Kidney

Cystic Diseases of the Kidney

Cystic Diseases of the Kidney

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Polycystic Overview - The Cystic Titans

ADPKD vs ARPKD: Gross, Microscopic, Clinical Features

FeatureADPKD (Autosomal Dominant)ARPKD (Autosomal Recessive)
GeneticsPKD1 (85%), PKD2 (15%)PKHD1 (fibrocystin)
InheritanceAutosomal DominantAutosomal Recessive
Age of OnsetAdults (30-50 yrs)Perinatal, infancy
Key FeaturesMassive bilateral cysts, enlarged kidneys, HTN, pain, hematuria, ESRDBilateral echogenic kidneys, small cysts (radial), oligohydramnios sequence (severe cases)
AssociatedHepatic cysts, Berry aneurysms (SAH risk), MVPCongenital hepatic fibrosis (CHF), portal HTN, Caroli syndrome

ADPKD - The Dominant Disruptor

  • Genetics: Autosomal dominant.
    • PKD1 (Chr 16, ~85%): Polycystin-1. More severe, earlier ESRD.
    • PKD2 (Chr 4, ~15%): Polycystin-2. Milder, later ESRD.
  • Pathophysiology: Defective polycystins → ciliary dysfunction → cyst formation.
  • Clinical Triad: Flank pain, hematuria, palpable kidneys. Hypertension common.
  • Extra-renal: Liver cysts (>70%), intracranial "berry" aneurysms (5-10%), MVP, colonic diverticula.

    ⭐ Intracranial berry aneurysms occur in 5-10% of ADPKD patients; rupture is a major cause of subarachnoid hemorrhage and mortality.

  • Diagnosis (Ultrasound - Ravine modified for +ve family history):
    • Age 15-39: ≥ 3 cysts (unilateral/bilateral).
    • Age 40-59: ≥ 2 cysts in each kidney.
    • Age ≥ 60: ≥ 4 cysts in each kidney.

ARPKD & NPHP/MCKD Complex - Recessive & Medullary Riddles

  • Autosomal Recessive Polycystic Kidney Disease (ARPKD):

    • Gene: PKHD1 (fibrocystin).
    • Presentation: Neonatal, Potter sequence.
    • Kidneys: Bilateral, enlarged, echogenic; radial cysts.
    • Liver: Congenital hepatic fibrosis (CHF), Caroli syndrome.

    ⭐ Congenital hepatic fibrosis is universally present in ARPKD and can lead to portal hypertension.

  • NPHP/MCKD Complex: Tubulointerstitial fibrosis, medullary cysts, progression to ESRD.

    • Nephronophthisis (NPHP):
      • AR; Childhood/Adolescent ESRD.
      • Kidneys: Normal/small, shrunken later; loss of corticomedullary differentiation (CMD).
      • Associations: Retinitis pigmentosa (Senior-Løken syndrome 📌), hepatic fibrosis, cerebellar ataxia.
    • Medullary Cystic Kidney Disease (MCKD):
      • AD (Types 1 & 2); Adult ESRD.
      • Kidneys: Similar to NPHP. UMOD gene (MCKD2).

Other Renal Cysts - Cyst Classification Capers

  • Simple Cysts: Common, benign, usually asymptomatic.
  • Complex Cysts (Bosniak Classification): Key for management. 📌 Mnemonic: "One Fine Fellow, Maybe Malignant" (I, II, IIF, III, IV)
    • I: Benign simple cyst. Malignancy risk: 0%.
    • II: Benign; few thin septa/calcifications. Malignancy risk: 0%.
    • IIF: Minimally complex; more septa/thicker calcifications. Requires Follow-up. Malignancy risk: ~5%.
    • III: Indeterminate; thick/irregular septa/walls, measurable enhancement. Malignancy risk: ~50%.
    • IV: Clearly malignant; enhancing soft tissue components. Malignancy risk: ~100%.

    ⭐ Bosniak category IV cysts have a nearly 100% risk of malignancy.

  • Acquired Cystic Kidney Disease (ACKD): Associated with long-term dialysis. Increased risk of RCC.
  • Medullary Sponge Kidney (MSK): Benign condition. Features medullary duct ectasia, nephrocalcinosis.

Bosniak classification of cystic renal masses

High‑Yield Points - ⚡ Biggest Takeaways

  • ADPKD: Most common inherited; PKD1 (chr 16) > PKD2; berry aneurysms, hepatic cysts.
  • ARPKD: PKHD1 (chr 6); infantile presentation, congenital hepatic fibrosis, Potter sequence.
  • Medullary Sponge Kidney: Benign; papillary collecting duct ectasia; recurrent stones, hematuria.
  • Nephronophthisis: Major cause of pediatric ESRD; tubulointerstitial fibrosis, corticomedullary cysts.
  • Acquired Cystic Disease: Develops in ESRD/dialysis patients; increased risk of renal cell carcinoma.
  • Von Hippel-Lindau: Multiple cysts; high risk of clear cell RCC, hemangioblastomas.
  • Simple Renal Cysts: Common, usually asymptomatic, benign; smooth, anechoic on ultrasound.

Practice Questions: Cystic Diseases of the Kidney

Test your understanding with these related questions

An 8 years old child suffering from recurrent attacks of polyuria since childhood presents to the pediatrics OPD. On examination, the child has short stature. Vitals and B.P. are normal. S. Creatinine - 6 mg/dL, HCO3 - 16 meq/L, S Na+ - 134 meq/L. On USG, bilateral small kidneys are seen. Diagnosis is:

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Flashcards: Cystic Diseases of the Kidney

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_____ kidney stones are characterized by urine crystals that are hexagonal in shape

TAP TO REVEAL ANSWER

_____ kidney stones are characterized by urine crystals that are hexagonal in shape

Cystine

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