title: Upbeat-torsional nystagmus and contralateral fourth-nerve palsy due to unilateral dorsal ponto mesencephalic lesion.
abstract: The central projections of the anterior semicircular canals are thought to be conveyed from the vestibular nuclei to the oculomotor nuclei in the midbrain by three distinct brainstem pathways: the medial longitudinal fasciculus, crossing ventral tegmental tract, and brachium conjunctivum. There is controversy as to whether upbeat nystagmus could result from lesions involving each of these pathways. We report a 52-year-old man who presented with a contralesional fourth-nerve palsy and primary-position upbeat-torsional nystagmus due to a small unilateral dorsal pontomesencephalic lymphomatous deposit. It is postulated that the upbeat-torsional nystagmus was caused by involvement of the brachium conjunctivum, which lies adjacent to the fourth-nerve fascicles at the dorsal pontomesencephalic junction, but involvement of the crossing ventral tegmental tract cannot be excluded. These observations suggest that, in humans, excitatory upward-torsional eye movement signals from the anterior semicircular canals could be partly conveyed to the midbrain by the brachium conjunctivum.
authors: Department of Neurology, University Hospitals Case Medical Center, Cleveland, Ohio, USA. mj.thurtell@gmail.com
authors: Matthew J
authors: MJ
authors: Thurtell
authors: Robert L
authors: RL
authors: Tomsak
authors: R John
authors: RJ
authors: Leigh
mesh_terms: D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008636:Mesencephalon / Q000473:pathology*; D008875:Middle Aged; D009759:Nystagmus, Pathologic / Q000150:complications* / Q000175:diagnosis; D020432:Trochlear Nerve Diseases / Q000150:complications* / Q000175:diagnosis