Primitive Neuroectodermal Tumor on the Buttock

ABSTRACT

Primitive neuroectodermal tumors (PNET) usually arise in the brain and central nervous system, but rarely occur outside of the brain, such as in the limbs, pelvis, paravertebral region or chest wall. Herein, a case of PNET on the buttocks is reported. A 24-year-old female was admitted for evaluation of a mass on her left buttock. An incisional biopsy revealed a primitive neuroectodermal tumor, with focal neural differentiation histologically. Preoperative MRI demonstrated the tumor was located in the subcutaneous layer of the left perineum, and extended to the ischiorectal fossa. The lesion showed an irregular, but well defined border; however, the differentiation from the left posterior wall of anus was focally obliterated. On operation, the tumor was not adhered to the surrounding structure, except for the external anal sphincter. The mass was completely resected. The tumor was about 8 x 9 x 5.8 cm in size, and the pathological evaluation confirmed a PNET, with a free anal sphincter margin. Therefore, chemoradiation therapy was planned, but the tumor recurred two months later. It was recommended the patient undergo a re-resection, but was lost before the procedure could be undertaken.