Malignant Peripheral Nerve Sheath Tumor in the Lesser Sac Masquerading as a Gastrointestinal Stromal Tumor of the Stomach: A Case Report

A malignant peripheral nerve sheath tumor (MPNST) is very rare, representing 3 - 10% of all soft tissue sarcomas. Approximately half of all such tumors are diagnosed in patients with neurofibromatosis type 1 (NF1). The extremities are involved most commonly, and the patient’s age is usually 20 - 50 years. Herein, we present a case of an MPNST that developed sporadically in an unusual location and in an unusually younger patient. A 16-year-old girl presented with dyspepsia and abdominal distension. Computed tomography (CT) demonstrated a well-defined mass approximately 12 cm in diameter in the lesser sac. The mass was composed principally of a heterogeneously enhancing solid portion and exhibited some cystic changes. Clinically and radiologically, the mass appeared to be a gastrointestinal stromal tumor of the stomach. The patient underwent exploratory laparotomy and mass excision. The surgical specimen revealed a solid firm mass measuring 13 × 13 × 6 cm. Histopathological and immunohistochemical analyses identified an MPNST. The patient underwent adjuvant chemotherapy but developed local recurrence with peritoneal seeding 8 months after surgery. Despite treatment with a different chemotherapeutic regimen, the disease progressed systemically and the patient died 3 years and 5 months after surgery. The uncommon tumor location and CT findings of our present MPNST case provide valuable information in terms of future clinical diagnoses of this rare but highly malignant disease..