Peripheral Nerve Sheath Tumors: Diagnosis Using Quantitative FDG-PET

Abstract

Malignant peripheral nerve sheath tumors (MPNST) compose a fraction of all soft tissue sarcomas, but are life-threatening and present difficult diagnostic and therapeutic challenges. Benign peripheral nerve sheath tumors, including schwannomas or neurofibromas, can often be managed conservatively unless symptomatic. MPNSTs require aggressive multimodality treatment (surgery, radiation therapy, ± chemotherapy). MPNSTs can arise from pre-existing neurofibromas in patients with neurofibromatosis type 1 (NF1) or can develop sporadically in the general population. Peripheral nerve sheath tumors are often pathologically heterogeneous or in difficult anatomic locations often making needle biopsy unreliable or unfeasible. Current standard imaging of these tumors rely on computed tomography (CT) or magnetic resonance imaging (MRI), both of which characterize size and local invasiveness, but do not provide reliable insight into the presence of malignant transformation. Clinical manifestations of malignant transformation classically rely on reported symptoms of new neurological deficits, rapid increase in size, change in palpated density from soft to hard, and unremitting pain. Investigations into the glycolytic phenotype of peripheral nerve sheath tumors with [18F] 2-Fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) have been performed to identify potential areas of malignant degeneration. Lower tumor FDG uptake has proven to correlate with benign peripheral nerve sheath tumors, which can be distinguished from the high FDG uptake of its malignant counterpart, MPNST. Clinicians may employ this imaging modality to help identify MPNSTs, guide biopsies, direct therapies, measure response to treatment, and survey for tumor recurrence.