Dear Dr. Roach: I am a 77-year-old female who recently had an abdominal and pelvic cat scan to rule out diverticulitis, and it came back showing a left staghorn calculus measured at 2-by-3 centimeters. This wasn't present in 2019. I have gas, gas pains, and diarrhea that is typical of IBS, which I have had for years. What causes this calculus, and is there treatment other than surgery?

— Anon.

Dear Anon.: A "staghorn" calculus is a kidney stone that has grown to fill up a large part of the collecting system of the kidney. Although a staghorn calculus has classically been associated with struvite (magnesium ammonium phosphate, a type of kidney stone that can only form in the presence of a high urinary pH, which is most typically caused by a chronic infection), staghorn calculi can consi

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