Extra-adrenal myelolipoma in the renal hilum: a case report and review of the literature.

Myelolipoma most commonly arises in the adrenal gland. Extra-adrenal myelolipomas are rare; to our knowledge, approximately 37 previous cases have been reported. We report a myelolipoma presenting as a localized mass in perirenal adipose tissue juxtaposed to the renal hilum in a 65-year-old Caucasian man who presented with back pain, weight loss, hematuria, and flank pain. The most likely diagnostic considerations were pyelonephritis or primary renal malignancy. However, histology revealed mainly mature adipose tissue along with multiple scattered islands of hematopoietic precursor cells. Representation of all the three hematopoietic cell lineages (granulocytic, erythroid, and megakaryocytic) was present. Perirenal masses such as morphologically identified myelolipomas are rarely, if ever, considered in differential diagnosis. The purpose of this report is to elicit consideration of extra-adrenal myelolipoma when formulating a differential diagnosis for perirenal and retroperitoneal tumors. Although primary and secondary malignant retroperitoneal tumors are much more common and aggressive neoplasms, establishing the correct diagnosis has important therapeutic and prognostic implications.