Nuclear pseudoinclusions in angiomyolipoma of the kidney. A case report

Fine needle biopsy has been utilized for the preoperative diagnosis of angiomyolipoma of the kidney. However, the spectrum of diverse nuclear morphology shown by the constituent smooth muscle cells of angiomyolipoma has not been fully elucidated.

An angiomyolipoma was found incidentally in the left kidney of an asymptomatic, 57-year-old woman, and nephrectomy was performed. The tumor was composed predominantly of smooth muscle cells occasionally showing atypical nuclear features. Small aggregates of adipocytes were also found. Direct stamp specimens of the tumor revealed plump, spindle-shaped smooth muscle cells, and the nuclei of many of these cells contained large pseudoinclusions (cytoplasmic invaginations). Histologic review of an additional four cases of renal angiomyolipoma further revealed the frequent occurrence of nuclear pseudoinclusions in smooth muscle cells of the tumor.

Nuclear pseudoinclusions on fine needle aspiration cytology of renal angiomyolipoma have not received adequate attention. We showed that this finding is a rather common nuclear feature in angiomyolipoma. It is presumably one of the manifestations of nuclear pleomorphism frequently seen in smooth muscle cells of angiomyolipoma and should not be considered an indication of malignancy.