Compensatory enlargement of an accessory spleen mimicking a retroperitoneal tumor: a case report.

We report a case of an accessory spleen in close relation to the upper pole of the left kidney, mimicking a retroperitoneal tumor. A 58-year-old asymptomatic woman was admitted to our department for the management of a retroperitoneal mass, when the structure was incidentally discovered by ultrasound scan. The patient reported having a splenectomy at a young age, due to echinococcal disease. The computed tomography and magnetic resonance imaging confirmed the presence of a solid retroperitoneal tumor (5 cm in diameter) in the lateral aspect of the left kidney. To rule out the presence of a malignant tumor, surgical exploration was performed. The macroscopic examination of the specimen revealed a well-circumscribed encapsulated mass, which appeared to have the typical features of splenic tissue. Histology confirmed that the mass was actually an accessory spleen. The retroperitoneal accessory spleen is a rare clinical entity. However, it should always be considered, when investigating a retroperitoneal mass, especially in patients who have had previous splenectomy.