Lumbar spinal nerves in the neural foramen: MR appearance. The appearance of the proximal lumbar spinal nerves at magnetic resonance (MR) imaging has not, to the authors' knowledge, been described. MR images and exactly corresponding sections obtained from four cadavers by means of a freezing microtome were correlated to characterize the MR appearance of the proximal spinal nerves. The junction of the dorsal and ventral rami with the dorsal and ventral roots consists of a group of six to 15 fascicles measuring 2-6 mm in length. These fascicles appear in MR images obtained with short repetition times as small foci of lower signal intensity than that of surrounding fat. The proximal spinal nerve and its relationship to the intervertebral disk and osseous margins of the neural foramen can be demonstrated effectively with MR imaging. 