Rapid Widespread Atypical Progressive Malignant Peripheral Nerve Sheath Tumor of Calf

Abstract Malignant peripheral nerve sheath tumors (MPNSTs) are rare, aggressive sarcomas with a high propensity for local recurrence and distant metastasis. We report a 66-year-old woman who presented with a painless swelling of the right calf. Following wide local excision, histopathology and immunohistochemistry confirmed MPNST with a high proliferative index. Within 2 months, the patient developed recurrent disease with extensive nodal involvement and extranodal metastasis.18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) performed for restaging demonstrated extensive FDG-avid retroperitoneal, pelvic, inguinal, femoral, and popliteal lymphadenopathy with multiple lytic skeletal and solitary lung metastases. This case highlights the aggressive nature of MPNST and the pivotal role of 18F-FDG PET/CT in detecting atypical widespread metastatic disease and guiding management.