[MR imaging appearances of schwannoma: correlation with pathological findings]

Peripheral schwannomas are nerve sheath neoplasms that consist of focal proliferation of Schwann cells. We reviewed the MRI findings in 17 patients with pathologically proved peripheral schwannomas. When compared with the signal intensity of muscle, that of the mass was isointense or hyperintense on T1-weighted images and hyperintense in all 17 tumors on T2-weighted images. All of the masses showed heterogeneous enhancement following the intravenous injection of Gd-DTPA on T1-weighted images. On T1-weighted images, hyperintensity was observed in the tumors that contained predominantly hypercellular Antoni type A tissue, while isointensity was observed in the tumors that contained predominantly hypocellular Antoni type B tissue. Relatively high signal intensity seen on T2-weighted images and Gd-DTPA enhanced T1-weighted images was observed in the tumors that contained predominantly Antoni type B tissue when compared with the signal intensity of tumors that contained predominantly Antoni type A tissue. A capsule was pathologically identified in 15 of 17 tumors. MRI correctly identified the presence of a capsule in 11 of 15 tumors and the absence of a capsule in one of 2 tumors. Thus the diagnostic accuracy was 71% (12/17). The cause of 4 false negative results appeared to be a hemorrhage or cystic change around the peripheral portion of the tumor, and it appeared to be a chemical artifact in one false positive result. Thus the appearance of MRI may suggest the cellular type of schwannoma, Antoni type A or B. However, prediction of the presence or absence of tumor capsule may be relatively difficult with MRI.