Fine needle aspiration cytodiagnosis of leiomyosarcoma of the renal pelvis. A case report with immunohistochemical study.

Leiomyosarcoma of the renal pelvis is extremely rare. We report one such case correctly diagnosed by ultrasound-guided fine needle aspiration cytology (FNAC). The FNAC smears showed a monotonous population of closely packed, spindled tumor cells arranged in interlacing bundles. Those cells possessed markedly pleomorphic, hyperchromatic, elongated nuclei and a moderate amount of eosinophilic, fibrillary cytoplasm. Fascicles of similar spindle tumor cells arranged in a whorled pattern were seen in the section of the cell block. Immunohistochemistry was performed on the sections of the cell block preparation, showing intensely positive cytoplasmic staining of the tumor cells for muscle-specific actin but negative staining for CAM 5.2, AE1/AE3, S-100 protein and HMB-45. This staining pattern of the tumor allows its differentiation from other primary sarcomas of the kidney, sarcomatoid renal cell carcinoma, peripheral nerve sheath tumor and renal angiomyolipoma. The extreme degree of nuclear pleomorphism and hyperchromatism is not to be expected in renal leiomyoma or the usual cases of mesoblastic nephroma. Besides delineating the FNAC features of leiomyosarcoma of the renal pelvis, the present case illustrates the value of using the cell block preparation in FNAC.