What are the sixth cranial nerve nuclear and fascicular lesions in multiple sclerosis (MS)?

Updated: Feb 21, 2019
  • Author: Fiona Costello, MD, FRCP; Chief Editor: Hampton Roy, Sr, MD  more...
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Answer

Answer

The paired abducens nuclei reside in the dorsal pons, separated from the floor of the fourth ventricle by the genu of the facial nerve (facial colliculus). [42] The abducens nucleus contains the neurons needed for horizontal gaze; interneurons travelling via the medial longitudinal fasciculus (MLF) connect the abducens nucleus with the contralateral oculomotor nucleus, coordinating abduction in one eye (governed by the lateral rectus) with adduction in the contralateral eye (medial rectus).

An abducens nuclear lesion causes horizontal gaze palsy ipsilateral to the side of the lesion, whereas a fascicular lesion causes ipsilateral abduction weakness with preserved adduction in the contralateral eye. Because of the proximity of the abducens nucleus to the facial nerve, patients may have a gaze palsy associated with a lower motor seventh nerve palsy, termed facial colliculus syndrome. [43] In one-and-a-half syndrome, an MS lesion involving the abducens nucleus and the ipsilateral MLF causes an ipsilateral gaze palsy and ipsilateral internuclear ophthalmoplegia (INO). [40] This causes either partial or complete loss of loss of horizontal gaze function, except for the abduction in the eye opposite from the INO, which may manifest features of abducting nystagmus. [40]


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