Nephrolithiasis and Cystic Kidney Disease
Core concepts
Stone types: calcium oxalate (most common), calcium phosphate, uric acid (radiolucent, alkaline urine dissolves), struvite (staghorn, urease producers), cystine (hexagonal, young patients). Evaluate with stone analysis, 24-hour urine, and serum chemistries. Acute colic: NSAIDs, fluids, alpha-blockers for distal stones; urgent decompression for infected obstruction.
Cystic disease: ADPKD (PKD1/PKD2, hypertension, hematuria, cysts, intracranial aneurysms, liver cysts), ARPKD (neonatal, Potter sequence), simple cysts, and medullary sponge kidney. ADPKD management: BP control, hydration, tolvaptan in selected patients, monitor for cyst hemorrhage and infection.
Traps
Uric acid stones are radiolucent-use CT. Struvite stones require complete removal and treatment of infection. Cystine stones need alkalinization and chelation. Infected obstructed kidney is an emergency-antibiotics plus drainage, not just antibiotics. ADPKD aneurysm screening in family history.
Rule of thumb
Any obstructed infected kidney = decompress; any recurrent stone former = 24-hour urine and stone analysis.
Worked example
A 40-year-old with ADPKD and sudden flank pain and hematuria: likely cyst hemorrhage; CT confirms; manage conservatively unless infection or obstruction.