Nerve sheath tumors are a distinct type of soft tissue tumors. The updated WHO classification of nerve sheath tumors includes several new benign and malignant nerve sheath tumor types. Imaging features suggestive for nerve sheath tumors include location near a nerve, fusiform shape, tail sign, split-fat sign, target sign, fascicular sign, and degenerative muscle changes. On imaging studies, the differential diagnosis between a schwannoma and a neurofibroma cannot be reliably made. MRI features suggestive of a schwannoma include a fascicular appearance on T2-weighted images and diffuse enhancement. Imaging findings suggestive of a neurofibroma include a target sign on T2-weighted images and central enhancement. Criteria that can be of help in establishing the diagnosis of malignant peripheral nerve sheath tumors (MPNSTs) include a large mass (>5 cm) with mass effect, perilesional edema, invasion of fat planes or neighboring structures, intratumoral cystic changes, peripheral contrast enhancement on static contrast-enhanced MRI, early arterial enhancement on dynamic contrast-enhanced (DCE) MRI, minimum apparent diffusion coefficient (ADC) values >1.1 × 10-3mm/s2 on diffusion-weighted imaging (DWI)/diffusion tensor imaging (DTI), trimethylamine (TMA) fraction >50 % on magnetic resonance spectroscopy (MRS), and SUVmax >3-4 on 18F-FDG PET. Nerve sheath tumors represent essential clinical manifestations of a group of inherited genetic disorders known as the neurofibromatoses. The three most widely recognized types of neurofibromatosis are neurofibromatosis type 1 (NF1), neurofibromatosis type 2 (NF2), and schwannomatosis. Plexiform neurofibromas are the hallmark lesion of NF1 and carry a lifetime risk of 10 % for malignant degeneration, necessitating vigilant surveillance. Due to the absence of any radiation exposure, whole-body MRI may be used for serial follow-up of individuals with NF1. 18F-FDG PET/CT allows a highly sensitive but less specific detection of MPNSTs and should be used in case of potential malignant transformation of nerve sheath tumors.
|Title of host publication||Imaging of Soft Tissue Tumors|
|Editors||Filip M Vanhoenacker, Paul M. Parizel, Jan L. Gielen|
|Place of Publication||Switzerland|
|Publisher||Springer International Publishing AG|
|Number of pages||32|
|Publication status||Published - 1 Jan 2017|