Malignant transformation in a sciatic plexiform neurofibroma in Neurofibromatosis Type 1 - imaging features that aid diagnosis

摘要

A 41-year-old Asian male with NF1 and bilateral sciatic plexiform neurofibromas, presented with unintentional weight loss, increasing size of a left thigh mass associated with increasing pain and radiculopathy. MRI of the left thigh demonstrated imaging features suspicious of malignant transformation. The patient had a new left lung mass, demonstrating avid FDG uptake, raising suspicion for metastasis. Surgical resection of the left thigh mass confirms malignant transformation in a preexisting sciatic plexiform neurofibroma. Diagnosis of malignant transformation in a nerve sheath tumour can be challenging. MRI remains the main preferred imaging modality in the evaluation of these tumours. Imaging features that raise suspicion for malignant transformation are discussed. Although none of these are specific for malignant transformation, studies suggest that the presence of two to four of these features should prompt further investigations. Keywords: Malignant peripheral nerve sheath tumour, MPNST, neurofibrosarcoma, neurofibromatosis type 1, NF1, plexiform neurofibroma, malignant transformation, MRI, CT, PETCASE REPORTClinical HistoryA 41-year-old Asian male presented with low-grade fever and unintentional loss of weight of 5kg over 5–6 months. He also complained of increasing size of his left thigh, associated with increasing pain and radiculopathy.The patient is a known case of Neurofibromatosis type 1 (NF1). He is also known to have bilateral sciatic plexiform neurofibromas. Clinical examination revealed multiple cutaneous neurofibromas and café-au-lait spots on his body and limbs. Clinically palpable soft tissue masses were felt in the bilateral posterior thighs, measuring up to 21 × 27 cm on the left, and 16 × 18 cm on the right. No obvious skin changes were detected.Imaging findingsBilateral lower limb radiographs demonstrated large posterior soft tissue masses in both thighs with no evidence of bony erosion, periosteal reaction, or pathological fracture (Figure 1). Open in a separate windowFigure 1 41-year-old male with NF1. Bilateral posterior thigh soft tissue masses noted, larger on the left.Findings: (a) Right femoral radiograph in lateral projection and (b) left femoral radiograph in lateral projection demonstrating bilateral posterior thigh soft tissue masses (*), larger on the left. No bony erosion, periosteal reaction or pathological fracture.Technique: (a) Right femoral radiograph in lateral projection (kVp: 73 and mAs: 8) and (b) left femoral radiograph in lateral projection (kVp: 73 and mAs: 8). Siemens Fluorospot Compact FD.