Primary intraosseous malignant peripheral nerve sheath tumor of the mandible: An unusual presentation mimicking a benign lesion.

The malignant peripheral nerve sheath tumor (MPNST) is a rare, aggressive malignant tumor that usually develops in the context of neurofibromatosis type 1. In the oral cavity, these tumors are excelling rare, especially in intraosseous sites. Herein, we report an unusual presentation of intraosseous MPNST affecting the mandible posterior region in a 28-year-old male without neurofibromatosis type 1 discovered as an incidental find on imaging exam. CT scan evaluation showed a solitary, well-defined, round hypodense lesion in the posterior mandibular region extending from tooth 45 to 46. Microscopic evaluation showed a tumor composed of atypical spindle-shaped cells arranged in fascicles and a storiform pattern. Tumor cells were positive for S-100 protein. Epithelial membrane antigen (EMA), pan-cytokeratin AE1/AE3, desmin, alpha-smooth muscle actin (α-SMA), HMB-45, MART-1, MUC4, and CD56 were negative. The diagnosis was low-grade MPNST. The patient underwent wide surgical resection of the tumor. After three years of follow-up, the patient remained with no evidence of recurrence or metastatic disease. When an intraosseous neurogenic tumor is suspected based on radiological characteristics, despite the apparent benign nature, an incisional biopsy is mandatory to rule out malignancy before treatment planning to avoid inadequate conservative treatment.