MR of benign peripheral nerve sheath tumors.

Seventeen benign peripheral nerve sheath tumors were studied using MR. In all cases T2 relaxation time, signal intensity on T1-weighted images (lesion/muscle ratio), detectability of nerve of origin, nerve-lesion relationship, and presence of a capsule were assessed. Sixteen tumors showed marked hyperintensity on T2-weighted images with T2 relaxation times values greater than 95 ms. One schwannoma was almost isointense with fat (T2 60 ms). All lesions were isointense with muscle on T1-weighted images. In schwannomas the nerve was usually situated at the periphery of the lesion and only in one case was it obliterated by the mass. In neurofibromas the nerve was either visible in a central position within the mass (two cases) or no longer visible (five cases). A capsule could be detected in 70% of the schwannomas and in 30% of the neurofibromas. In patients with soft tissue masses, MR may contribute to recognition of nerve sheath tumors by showing the nerve of origin and typical signal hyperintensity on T2-weighted images. It can also be helpful in distinguishing between schwannomas and neurofibromas by the location of the nerve of origin and the presence of a capsule.