title: Somatotopic organization of the corticospinal tract in the human brainstem: a MRI-based mapping analysis.
abstract: To investigate the incompletely understood somatotopical organization of the corticospinal tract in the human brainstem, we performed a voxel-based statistical analysis of standardized magnetic resonance scans of 41 prospectively recruited patients with pyramidal tract dysfunction caused by acute brainstem infarction. Motor hemiparesis was rated clinically and by the investigation of motor evoked potentials to arms and legs. Infarction affected the pons in 85% of cases. We found the greatest level of significance of affected brainstem areas between the pontomesencephalic junction and the mid pons. Lesion location was significantly more dorsal in patients with hemiparesis affecting more proximal muscles and was significantly more ventral in patients with predominantly distal limb paresis. Comparison of magnetic resonance lesion from patients with paresis predominantly affecting arm or leg did not show significant topographical differences. We conclude that a topographical arm/leg distribution of corticospinal fibers is abruptly broken down as the descending corticospinal tract traverses the pons. Corticospinal fibers, however, follow a somatotopical order in the pons with fibers controlling proximal muscles being located close to the reticular formation in the dorsal pontine base, and thus more dorsal than the fibers controlling further distal muscle groups.
authors.affiliation: Department of Neurology, Johannes Gutenberg-University Mainz, Mainz, Germany. marx@neurologie.klinik.uni-mainz.de
authors.forename: Juergen J
authors.initials: JJ
authors.lastname: Marx
authors.forename: Gian D
authors.initials: GD
authors.lastname: Iannetti
authors.forename: Frank
authors.initials: F
authors.lastname: Thömke
authors.forename: Sabine
authors.initials: S
authors.lastname: Fitzek
authors.forename: Peter P
authors.initials: PP
authors.lastname: Urban
authors.forename: Peter
authors.initials: P
authors.lastname: Stoeter
authors.forename: Giorgio
authors.initials: G
authors.lastname: Cruccu
authors.forename: Marianne
authors.initials: M
authors.lastname: Dieterich
authors.forename: Hanns C
authors.initials: HC
authors.lastname: Hopf
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001931:Brain Mapping; D020526:Brain Stem Infarctions / Q000473:pathology* / Q000503:physiopathology; D038524:Diffusion Magnetic Resonance Imaging; D019054:Evoked Potentials, Motor; D006801:Humans; D021621:Imaging, Three-Dimensional; D008875:Middle Aged; D010291:Paresis / Q000473:pathology* / Q000503:physiopathology; D011149:Pons / Q000473:pathology* / Q000503:physiopathology; D011446:Prospective Studies; D011712:Pyramidal Tracts / Q000473:pathology* / Q000503:physiopathology