Aberrant regeneration of the oculomotor nerve: implications for neurosurgeons.

Aberrant regeneration of cranial nerve III, otherwise known as oculomotor synkinesis, is an uncommon but well-described phenomenon most frequently resulting from trauma, tumors, and aneurysms. Its appearance usually follows an oculomotor palsy, but it can also occur primarily without any preceding nerve dysfunction. It is vital that neurosurgeons recognize this disorder because it may be the only sign of an underlying cavernous tumor or PCoA aneurysm. The tumor most often implicated is a cavernous or parasellar meningioma, but any tumor that causes compression or disruption along the course of the oculomotor nerve may cause primary or secondary misdirection. The most common clinical signs of oculomotor synkinesis consist of elevation of the upper eyelid on attempted downward gaze or adduction, adduction of the eye on attempted upward or downward gaze, and constriction of the pupil on attempted adduction. The authors present the largest series of patients with oculomotor synkinesis, including those in whom it developed after neurosurgical intervention, to illustrate various presentations. In addition, the various mechanisms that contribute to synkinesis are reviewed. Last, the treatment strategies for both oculomotor palsies and synkinesis are discussed.