When a Forgotten Kidney Stone Breaks Free: An Unexpected Case of Spontaneous Nephrocutaneous Fistula.

Nephrocutaneous fistula (NCF) is an exceptionally rare urological entity, most often arising as a late complication of neglected renal calculi, chronic pyelonephritis, or renal tuberculosis. Spontaneous extrusion of renal stones through such fistulous tracts is even less frequently documented. We describe the case of an 85-year-old woman who presented with spontaneous extrusion of a large staghorn calculus through a lumbar cutaneous opening. The patient had a decade-long history of untreated renal stones and a non-functioning kidney, repeatedly declining definitive surgical management. Imaging confirmed a fistulous tract connecting the kidney to the skin with residual calculi. Given her advanced age and comorbidities, she opted for conservative management with antibiotics, analgesia, and wound care. This case underscores the severe consequences of untreated renal calculi, highlights the diagnostic role of imaging in defining fistulous anatomy, and emphasizes the importance of timely surgical intervention, especially in cases of non-functioning kidneys, to prevent such rare but debilitating outcomes.