Malignant spindle cell tumor of the anal canal, what are the differential diagnoses?

Malignant peripheral nerve sheath tumor (MPNST) is an uncommon tumor. Here, we report a case of rectal MPNST. The patient was a 75 year old man with symptoms and signs of a mass protruded from anus. There was no evidence of neurofibromatosis type 1 in him or his family. Primary diagnosis was hemorrhoid. Biopsy was taken. The microscopic examination revealed spindle cells with large and hyperchromatic nuclei. Mitotic figures were numerous. Routine and ancillary techniques confirmed the diagnosis of MPNST. MPNST should be distinguished from more common lesions encountered at this anatomic site such as hemorrhoid, malignant melanoma, sarcomatoid carcinoma, and gastrointestinal stromal tumor.