A new method to investigate brain stem structural-functional correlations using digital post-processing MRI - reliability in ischemic internuclear ophthalmoplegia

We investigated the reliability of a new digital post-processing magnetic r esonance imaging (MRI) technique in ischemic brain stem lesions to identify relations of the lesion to anatomical brain stem structures. The target wa s a medial longitudinal fasciculus (MLF) lesion, which was evident from ips ilateral internuclear ophthalmoplegia (INO). Sixteen patients with acute un ilateral INO and an isolated acute brain stem lesion in T2- and EPI-diffusi on weighted MRI within 2 days after the onset of symptoms were studied. The MRI slice direction was parallel and perpendicular to a slice selection of a stereotactic anatomical atlas. The individual slices were normalized and projected in the digitalized atlas. The eye movement disorder was monitore d by electro-oculography. In all patients with clinical or subclinical elec tro-oculographically documented INO and MRI proven brain stem infarction th e lesion covered or at least partially overlapped the ipsilateral MLF at on e or more atlas levels. We conclude that digital post-processing MRI with n ormalizing and projecting brain stem lesions in an anatomical atlas is a re liable method to demonstrate the anatomical structures involved by the lesi on. Combined with electrophysiological brain stem testing, this method may be a useful tool to identify incompletely understood pathways mediating bra in stem reflexes or the generators of evoked potentials.