<P> Rare causes of isolated sixth nerve damage include Wernicke - Korsakoff syndrome and Tolosa - Hunt syndrome . Wernicke - Korsakoff syndrome is caused by thiamine deficiency, classically due to alcoholism . The characteristic ocular abnormalities are nystagmus and lateral rectus weakness . Tolosa - Hunt syndrome is an idiopathic granulomatous disease that causes painful oculomotor (especially sixth nerve) palsies . </P> <P> Indirect damage to the sixth nerve can be caused by any process (brain tumor, hydrocephalus, pseudotumor cerebri, hemorrhage, edema) that exerts downward pressure on the brainstem, causing the nerve to stretch along the clivus . This type of traction injury can affect either side first . A right - sided brain tumor can produce either a right - sided or a left - sided sixth nerve palsy as an initial sign . Thus a right - sided sixth nerve palsy does not necessarily imply a right - sided cause . Sixth nerve palsies are infamous as "false localizing signs ." Neurological signs are described as "false localizing" if they reflect dysfunction distant or remote from the expected anatomical location of pathology . Isolated sixth nerve palsies in children are assumed to be due to brain tumors until proven otherwise . </P> <P> Damage to the abducens nucleus does not produce an isolated sixth nerve palsy, but rather a horizontal gaze palsy that affects both eyes simultaneously . The abducens nucleus contains two types of cells: motor neurons that control the lateral rectus muscle on the same side, and interneurons that cross the midline and connect to the contralateral oculomotor nucleus (which controls the medial rectus muscle of the opposite eye). In normal vision, lateral movement of one eye (lateral rectus muscle) is precisely coupled to medial movement of the other eye (medial rectus muscle), so that both eyes remain fixed on the same object . </P> <P> The control of conjugate gaze is mediated in the brainstem by the medial longitudinal fasciculus (MLF), a nerve tract that connects the three extraocular motor nuclei (abducens, trochlear and oculomotor) into a single functional unit . Lesions of the abducens nucleus and the MLF produce observable sixth nerve problems, most notably internuclear ophthalmoplegia (INO). </P>

Where does the abducens nerve exit the skull