MRI anatomy of white matter layers around the trigone of the lateral ventricle.

MRI was obtained in eight normal volunteers and seven patients with brain oedema around the trigone. In addition to the conventional sequences, diffusion-weighted and intravoxel-incoherent-motion images using motion-proving anteroposterior and/or lateral direction gradients were obtained to show the white matter pathways better. Coronal proton-density-weighted images showed three thin relatively high-intensity layers in addition to the tapetum and the internal and external sagittal strata. Although they have not been confirmed anatomically, the thin layer between the internal and the external sagittal strata was corroborated by diffusion-weighted and intravoxel-incoherent-motion images, and by characteristics of the spread of oedema into the sagittal stratum. We propose that this layer be named the central sagittal lamina. The other two layers medial and lateral to the sagittal stratum were outside, but in contact with the medial and lateral parts of the sagittal stratum, respectively. We provisionally named them medial and lateral sagittal laminae; they were not evident on any other images. The low-intensity layer on T2-weighting was the internal sagittal stratum. The optic radiation, comprising the external sagittal stratum, appeared as an intermediate to slightly high-intensity layer on T2-weighted images and a low-intensity layer on T1-weighted images as did the corticospinal tract in the posterior internal capsule.