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

Abstract

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.

Introduction

The malignant peripheral nerve sheath tumor (MPNST) is a rare, aggressive malignant tumor that comprises about 10% of all soft tissue sarcomas [1]. About 50% of these tumors occur in individuals with neurofibromatosis type 1 (NF-1). However, they can also be induced by radiation or occur sporadically [1], [3]. MPNSTs are rare in the oral cavity, especially within the jawbones, corresponding to about 0.5% of all oral sarcomas [4]. The diagnosis of MPNSTs has been described as one of the most difficult due to its non-specific clinical and histopathological presentation [1], [5].

Most previous reports of intraosseous MPNSTs have shown an ill-defined irregular, osteolytic radiolucency causing expansion, thinning, perforation of the cortical plates, and root resorption of involved teeth in radiographs [6], [7], [8], [9]. Unilocular lesions with well-defined borders are excelling uncommon [2]. In these circumstances, MPNSTs can be misdiagnosed as benign lesions leading to an incorrect therapeutic approach.

Herein, we report an uncommon presentation of intraosseous MPNST in the mandible without association with NF-1 discovered as an incidental finding in a CT imaging examination mimicking a benign lesion.