MR measurement of normal and pathologic brainstem diameters.

The dimensions of the brainstem were measured on magnetic resonance (MR) images to provide criteria for detecting brainstem enlargement. Twenty-eight normal adult subjects had MR imaging with sagittal partial-saturation and spin-echo sequences. Four patients with brainstem gliomas and three with cerebellar atrophy were also studied. Five measurements were made: (A) the distance between the interpeduncular fissure and the aqueduct, (B) the distance from the anterior surface of the cerebral peduncles to the aqueduct, (C) the distance between the anterior surface of the pons midway between the mesencephalon and medulla to the fourth ventricular floor, (D) the shortest anteroposterior diameter of the medulla at the pontomedullary junction, and (E) the shortest anteroposterior diameter of the medulla at the medullospinal junction. Pontine diameter could be measured more reproducibly and accurately than mesencephalic or medullary diameters. In four patients with glioma, one or more of the measured diameters were more than 2 SDs above the average in normal volunteers, and abnormally small measurements were found in the patients with atrophy.