Endourology and Urolithiasis
Core concepts
Stone disease is high-yield for both pathophysiology and procedural selection. Know stone composition and risk factors: calcium oxalate (hypercalciuria, hyperoxaluria, low citrate), struvite (infection with urease producers such as Proteus), uric acid (low urine pH, radiolucent), cystine (hexagonal crystals, cystinuria). Understand metabolic evaluation for recurrent or high-risk stone formers. Procedural selection depends on size and location: ureteroscopy for distal ureteral stones and for many renal stones; shockwave lithotripsy for suitable renal stones <2 cm; percutaneous nephrolithotomy for large (>2 cm) or complex stones and staghorn calculi. Know the management of obstructing stones with infection (urgent decompression by stent or nephrostomy). Understand ureteral access sheath use, laser lithotripsy principles, and complications such as ureteral injury and sepsis.
Traps
Questions test the first step in an infected obstructed system - decompression, not definitive stone removal. Struvite stones require complete removal because residual fragments perpetuate infection. Uric acid stones can be dissolved by alkalinization, but struvite cannot. Radiologic pitfalls: uric acid stones are radiolucent on plain film; all stones except pure uric acid are visible on CT.
Worked example / rule of thumb
A febrile patient with an obstructing 8 mm proximal ureteral stone: the answer is urgent decompression (stent or percutaneous nephrostomy) plus antibiotics, then definitive stone treatment later. Rule of thumb: infection plus obstruction equals drainage first.