Background: The incidence of accessory spleens is usually related to hematologic and rheumatoid disorders or previous traumatic splenectomy. Pelvic accessory spleen is a rare entity, often unsuspected preoperatively and it usually mimicks a retroperitoneal tumor. Case Report: An unusual case of pelvic accessory spleen mimicking common iliac artery aneurysm in 56-year-old man is described. The patient had neither history of splenectomy nor of hematologic and rheumatoid diseases. He presented a 6-month history of discomfort and palpable pulsating mass in the right lower abdomen. US of the abdomen demonstrated an oval mass 5 cm in diameter, strictly connected to the right common iliac artery and presumed to be its aneurysm. A CT scan of the abdomen and color flow duplex sonography excluded the aneurysm of the right iliac artery, but malignant growth could not be ruled out preoperatively so the patient was qualified for surgery. During the operation, an encapsulated and well-circumscribed tumor below the aortic bifurcation was removed and on histological examination it showed the characteristics of splenic tissue. This is the 13th case of pelvic accessory spleen described in the medical literature. The previously published cases and the possibility of nonsurgical diagnosis are discussed. Conclusions: Preoperative diagnosis of pelvic accessory spleen remains still diagnostic challenge especially in patients without previous splenectomy and/or hematologic diseases.

Keywords: pelvic accessory spleen, iliac artery aneurysm, Retroperitoneal Space, Diagnosis, Surgery