MR SIGNAL INTENSITY OF THE OPTIC RADIATION

PURPOSE: To determine whether a hyperintense layer adjacent to the lat eral ventricle on T2-weighted MR images represents the optic radiation . METHODS: We reviewed 11 brain specimens from patients with nonneurol ogic diseases and MR images from 43 healthy volunteers. The MR images in a patient with cerebral infarction involving the lateral geniculate body were also reviewed to evaluate wallerian degeneration of the opt ic radiation. RESULTS: The external sagittal stratum, composed of the optic radiation, showed a pale layer in specimens stained by Bodian's method. On high-power microscopic views of the specimens, the axons of the external sagittal stratum were large and separated by wide transl ucent spaces. In the volunteers, the external sagittal stratum appeare d hyperintense on T2-weighted MR images and hypointense on T1-weighted images. The MR images in a patient with cerebral infarction showed hy perintensity within the layer corresponding to the external sagittal s tratum. CONCLUSIONS: The hyperintense layer on T2-weighted images repr esents the external sagittal stratum, or optic radiation. The signal i ntensity of the external sagittal stratum reflects histologic characte ristics of low axonal density.