Gossypiboma mimicking a retroperitoneal tumor.

"Gossypiboma" denotes a mass of cotton that is retained in the body after surgery. An image is presented of a retroperitoneal mass in a lady who had a right nephrectomy 8 years earlier for a nonfunctioning kidney. Clinical examination and plain abdominal radiography were not contributory. Contrast-enhanced abdominal computed tomography revealed a well-defined, heterogeneous, spherical, soft-tissue mass, 13 × 9 × 9 cm in size, in the retroperitoneum, with a dense enhanced wall, abutting the right psoas and posterior abdominal wall. Exploration revealed an abdominal sponge surrounded by foreign body granuloma adherent to surrounding structures. Gossypiboma can mimic a tumor and is a diagnostic challenge.