Imprint Cytology of Extrarenal Retroperitneal Angiomyolipoma: A Case Report

Renal angiomyolipoma (AML) is recognized as a benign renal tumor composed of atypical blood vessels, smooth muscle and fat tissue, and constitutes about 1% of all renal masses. In contrast, extrarenal AMLs are extremely rare tumors of which there have been less than 70 reported cases since they were first described in 1982. We present the case of a 65-year-old female with a retroperitoneal extrarenal mass. Histopathological examination and HMB-45 staining revealed the mass to be an extrarenal AML.

A 65-year-old female presented with a 2cm mass next to the pancreas head during a follow-up CT scan one year after chemotherapy for malignant lymphoma. Diagnosis of the tumor was not possible with EUS-FNA cytology. The tumor was considered to be a solid-pseudopapillary neoplasm (SPN) or endocrine tumor of the pancreas. Subsequently, surgical resection of the tumor was performed.

Gross microscopic examination of the tumor, which was located in the retroperitoneum and was separated from the pancreas, showed histologically tortuous thick blood vessel with bundles of smooth muscle. Mature adipose tissue was also detected. Imprint cytology of the cut surface of the tumor showed atypical cells which had spindle shaped outlines, nuclear enlargement and hyperchromasia. HMB-45 staining performed on the larger lesion was positive, which is characteristic of AMLs.

Extrarenal AMLs are rare and occur most commonly in the liver. Lesions in the retroperitoneum require definitive diagnosis since they can mimic other benign and malignant retropelitoneal tumors, which must be differentiated.

Keywords: Angiomyolipoma, Blood vessel, Fat tissue, Renal tumor, Smooth muscle.