Stag horn calculus - Urinary stones

Stag horn calculus

Definition

A urinary stone which fills the calyces and pelvis of a kidney, these are usually associated with infection and are formed of struvite.

Aetiology/pathophysiology

Stag horn calculi are struvite stones (i.e. formed of struvite and calcium carbonate-apatite). Infection with Proteus or Klebsiella causes increased amounts of ammonia, due to the presence of urease (which breaks down urea into ammonia and carbon dioxide). This increases the amount of ammonium, but also alkalinises the urine, decreasing the solubility of phosphate. Infection can also be a complication of stones.

Clinical features

May be asymptomatic in early stages. Later, pain, haematuria and impaired renal function.

Investigations

As for urinary stones. Assess the kidney function with radionuclide imaging. If <10% renal function the kidney should be removed. If there is >25% function in a younger patient many would probably try to preserve the kidney.

Management

Open surgery, or very slow gradual breaking up of the calculus using ‘percbang’ combination therapy, which involves placing a stent from the kidney to the bladder for stones to descend, then debulking the stone with repeated lithotripsy. Nephrectomy is advised for a symptomatic stag horn calculus in a poorly functioning kidney.