TAILIEUCHUNG - Chapter 029. Disorders of the Eye (Part 21)

Abducens Nerve The sixth cranial nerve innervates the lateral rectus muscle. A palsy produces horizontal diplopia, worse on gaze to the side of the lesion. A nuclear lesion has different consequences, because the abducens nucleus contains interneurons that project via the medial longitudinal fasciculus to the medial rectus subnucleus of the contralateral oculomotor complex. Therefore, an abducens nuclear lesion produces a complete lateral gaze palsy, from weakness of both the ipsilateral lateral rectus and the contralateral medial rectus. Foville's syndrome following dorsal pontine injury includes lateral gaze palsy, ipsilateral facial palsy, and contralateral hemiparesis incurred by damage to descending. | Chapter 029. Disorders of the Eye Part 21 Abducens Nerve The sixth cranial nerve innervates the lateral rectus muscle. A palsy produces horizontal diplopia worse on gaze to the side of the lesion. A nuclear lesion has different consequences because the abducens nucleus contains interneurons that project via the medial longitudinal fasciculus to the medial rectus subnucleus of the contralateral oculomotor complex. Therefore an abducens nuclear lesion produces a complete lateral gaze palsy from weakness of both the ipsilateral lateral rectus and the contralateral medial rectus. Foville s syndrome following dorsal pontine injury includes lateral gaze palsy ipsilateral facial palsy and contralateral hemiparesis incurred by damage to descending corticospinal fibers. Millard-Gubler syndrome from ventral pontine injury is similar except for the eye findings. There is lateral rectus weakness only instead of gaze palsy because the abducens fascicle is injured rather than the nucleus. Infarct tumor hemorrhage vascular malformation and multiple sclerosis are the most common etiologies of brainstem abducens palsy. After leaving the ventral pons the abducens nerve runs forward along the clivus to pierce the dura at the petrous apex where it enters the cavernous sinus. Along its subarachnoid course it is susceptible to meningitis tumor meningioma chordoma carcinomatous meningitis subarachnoid hemorrhage trauma and compression by aneurysm or dolichoectatic vessels. At the petrous apex mastoiditis can produce deafness pain and ipsilateral abducens palsy Gradenigo s syndrome . In the cavernous sinus the nerve can be affected by carotid aneurysm carotid cavernous fistula tumor pituitary adenoma meningioma nasopharyngeal carcinoma herpes infection and Tolosa-Hunt syndrome. Unilateral or bilateral abducens palsy is a classic sign of raised intracranial pressure. The diagnosis can be confirmed if papilledema is observed on fundus examination. The mechanism is still debated but is .

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