Iliopsoas involvement complicating longstanding nephrolithiasis with chronic infection: a three-patient case series reconsidering “malignant lithiasis”

Background Severe complications of longstanding nephrolithiasis with chronic infection remain clinically relevant despite continuing advances in endourological techniques. This phenotype may extend beyond the collecting system, resulting in extensive retroperitoneal infection with extrarenal extension, irreversible renal functional loss, and, in rare instances, occult malignancy. Reconsidering the historical descriptor “malignant lithiasis” may help frame this aggressive clinical trajectory, particularly in patients with delayed presentation or limited access to timely care. Case presentation: We report three cases of longstanding nephrolithiasis with chronic infection with iliopsoas involvement. Case 1 was a 50-year-old woman with perinephric and iliopsoas abscesses, with inferior tracking along the iliopsoas compartment into the obturator region. Case 2 was a 53-year-old man with perinephric and iliopsoas abscesses and inflammatory involvement extending to the colon. Case 3 was a 59-year-old man with a large renal abscess who underwent nephrectomy to achieve definitive source control for uncontrolled infection, revealing an incidental diagnosis of renal pelvic squamous cell carcinoma. Across cases, infection was recurrent or refractory, temporizing measures (e.g., percutaneous drainage and/or nephrostomy) did not achieve sustained definitive source control, and two patients developed non-functioning kidneys requiring nephrectomy after infection control. Conclusions These cases illustrate an aggressive phenotype of longstanding nephrolithiasis with chronic infection, consistent with “malignant lithiasis” as a marker of clinical severity rather than malignant histology. Recognizing red flags—recurrent or refractory infection, imaging evidence of extrarenal extension (e.g., iliopsoas and perinephric involvement), and progressive functional decline—may support timely escalation to definitive source control. Routine histopathology of nephrectomy specimens is critical to minimize missed malignancy in stone-related non-functioning kidneys.