Large Malignant Peripheral Nerve Sheath Tumor Arising From the Sciatic Nerve in a Patient With Neurofibromatosis Type 1.

Malignant peripheral nerve sheath tumors (MPNSTs) are rare and aggressive soft tissue sarcomas arising from peripheral nerves or through the malignant transformation of preexisting benign nerve sheath tumors, particularly in patients with neurofibromatosis type 1 (NF1). Sciatic nerve involvement is uncommon and presents major diagnostic and surgical challenges because of the risk of significant functional impairment. A 21-year-old man with NF1 presented with a one-year history of a rapidly progressive right thigh mass associated with pain and severe motor deficit of the lower limb. Magnetic resonance imaging showed a large heterogeneous intramuscular mass in the posterior compartment of the right thigh, measuring 167 × 100 × 84 mm, with intratumoral necrotic areas and close continuity with the sciatic nerve. Core needle biopsy confirmed MPNST. After active bleeding developed at the biopsy site, urgent surgical resection was performed. Intraoperatively, the tumor was found to involve the sciatic nerve, particularly its common peroneal division, which required sacrifice during excision. A redundant plexiform neurofibroma on the medial aspect of the thigh was also excised separately. Histopathological examination confirmed the Fédération Nationale des Centres de Lutte Contre le Cancer (FNCLCC) grade 3 MPNST with negative surgical margins. The patient subsequently received adjuvant radiotherapy and chemotherapy. At the two-year follow-up, there was no evidence of local recurrence or distant metastasis, and neurological status remained stable with rehabilitation. This case highlights the diagnostic complexity and surgical difficulty of giant sciatic nerve MPNST in a patient with NF1. Early recognition, complete surgical resection, and multidisciplinary management are essential to optimize oncologic outcomes.