Retroperitoneal abscess caused by dropped renal stones

Staghorn calculi account for about 4% of presenting renal stones in developed countries, are source of recurrent urinary tract infection, and may be eventually treated by surgical stone removal. A 55-year-old female with a history of staghorn renal calculi and recurrent urinary tract infections presented with a left flank and lower abdominal pain following recent left robotic partial nephrectomy and nephrolithotomy. Contrast-enhanced computed tomography (CT) of the abdomen demonstrated a large left-sided retroperitoneal fluid collection with a few dropped renal stones in the dependent portion of the collection. The patient treated with early percutaneous drainage of the collection and antibiotic treatment and responded well clinically. The clinical and imaging presentation of a rare case of retroperitoneal abscess formation caused by dropped renal stones is described in this study. Imaging, particularly ultrasound and CT, plays a key role in detecting the dropped renal stones and can help with differential diagnosis and treatment plans.