Malignant peripheral nerve sheath tumor in an elderly patient with superficial spreading melanoma: A case report

BACKGROUND: Malignant peripheral nerve sheath tumor (MPNST) is a type of spindle cell sarcoma originating from the peripheral nerve, which usually results in the corresponding nerve sign on magnetic resonance imaging (MRI). Patients with MPNST may also have neurofibromatosis type 1. CASE SUMMARY: A 78-year-old male was admitted to the hospital due to a tumor in his left knee. He had a previous history of superficial spreading melanoma on the left thigh. Color Doppler ultrasonography showed a hypoechoic mass in the subcutaneous soft tissues of the medial left knee with an abundant rich blood flow. Computed tomography scanning did not show obvious signs of bone destruction, but the skin adjacent to the tumor was slightly thickened. MRI examination revealed that the hypervascular lesion was well-circumscribed, lobulated, invaded the surrounding soft tissues and demonstrated heterogeneous enhancement but lacked an entering and exiting nerve sign. The MRI result indicated the invasiveness of the tumor. The patient underwent a left knee joint mass expanded resection and the first histopathological examination showed a MPNST with positive surgical margins. Therefore, the second extended resection was performed, and the patient had a good outcome in the short term. CONCLUSION: MRI is a useful technique for revealing the biological characteristics of MPNST and provides clinical support for evaluation of the surgical area before operation.