Urolithiasis and Cystic Kidney Disease

Urolithiasis (Kidney Stones)

• Kidney stones obstruct urine flow, potentially causing pain, infection, and renal damage.
• Stones form in the urinary tract and can obstruct ureters, renal pelvis, or urethra, leading to hydronephrosis and renal impairment.

Cystic Kidney Disease

• Autosomal Dominant Polycystic Kidney Disease (ADPKD):
  • Inherited condition with numerous fluid-filled cysts in the kidneys, often leading to renal failure.
  • Autosomal dominant pattern; mutations in PKD1 or PKD2 genes.
• Autosomal Recessive Polycystic Kidney Disease (ARPKD):
  • Rare form of polycystic kidney disease presenting early in life with cystic dilations of the renal collecting ducts.
  • Autosomal recessive pattern; mutation in the PKHD1 gene.

Etiologies of Kidney Stones

• Calcium Oxalate Stones:
  • Most common type.
  • Formed due to hypercalciuria, hyperoxaluria, or hypocitraturia.
  • Crystalline structure composed of calcium oxalate.
• Struvite Stones:
  • Formed by infection with urease-producing bacteria (e.g., Proteus).
  • "Staghorn" appearance, large and branching.
• Uric Acid Stones:
  • Associated with acidic urine and hyperuricemia (gout).
  • Radiolucent stones, typically small and yellowish.
• Cystine Stones:
  • Rare, seen in cystinuria (genetic disorder affecting amino acid reabsorption).
  • Hexagonal crystals under a microscope.

Pathophysiology of Kidney Stone Formation

• Supersaturation of Urine: Excessive minerals like calcium, oxalate, or uric acid precipitate into crystals.
• Nucleation and Growth: Small crystals aggregate into stones over time, leading to obstruction and possible infection.
• Obstruction: Stones lodge in the ureter, causing colicky pain, hematuria, and potentially hydronephrosis.

Pathophysiology of Cystic Diseases

• ADPKD: Cysts arise from renal tubules and collecting ducts, gradually expanding and compressing functional nephrons, leading to progressive renal failure.
  • Other effects: Hypertension, liver cysts, and intracranial aneurysms.
• ARPKD: Characterized by collecting duct dilation and fibrosis, leading to severe renal dysfunction and complications like congenital hepatic fibrosis.

Clinical Manifestations of Urinary Tract Obstruction (Kidney Stones)

• Symptoms: Severe flank pain (renal colic), hematuria, nausea, vomiting, urinary urgency, and sometimes fever (if infection is present).
• Complications: Hydronephrosis, recurrent UTIs, and renal damage.

Clinical Manifestations of Cystic Kidney Disease (ADPKD)

• Symptoms: Hypertension, hematuria, flank pain, urinary tract infections, and kidney failure in advanced stages.
• Extrarenal Manifestations: Liver cysts, aneurysms, diverticulosis, and mitral valve prolapse.

Clinical Manifestations of Cystic Kidney Disease (ARPKD)

• Symptoms: Present in infancy with renal failure, hypertension, enlarged kidneys, and breathing difficulties due to pulmonary hypoplasia.
• Complications: Congenital hepatic fibrosis leading to portal hypertension.

Laboratory and Imaging Findings

• Calcium Stones:
  • Imaging: Radiopaque on X-rays and CT scans.
  • Urinalysis: Hematuria, presence of calcium oxalate crystals.
• Struvite Stones:
  • Imaging: Radiopaque, large stones with staghorn appearance.
  • Urinalysis: Infection markers (e.g., leukocytes, nitrites), alkaline urine.
• Uric Acid Stones:
  • Imaging: Radiolucent, only visible on ultrasound or CT scan.
  • Urinalysis: Low pH (acidic urine).
• Cystine Stones:
  • Imaging: Radiopaque, hexagonal crystals on X-rays and CT scans.
  • Urinalysis: High cystine levels.