aberrant regeneration

Aberrant regeneration is the misdirected regrowth of third nerve fibers after an oculomotor nerve palsy, also called oculomotor synkinesis. The regenerating axons reach the wrong targets. An impulse that once produced only adduction may now also elevate the lid or constrict the pupil.^1,2 Aberrant regeneration follows acute traumatic and compressive third nerve palsies, but not vascular ones, because the endoneural nerve sheaths stay intact in vascular lesions.³

The two most common signs are lid elevation, called the pseudo-Graefe sign, and pupillary constriction, each appearing on adduction, downgaze or both.^1,3 The pupil may constrict during adduction yet fail to constrict to light.²

Secondary aberrant regeneration appears in the recovery phase several weeks after an acute third nerve palsy from trauma, ophthalmoplegic migraine, pituitary apoplexy or inflammation.² Primary aberrant regeneration appears with no preceding palsy and points to a slowly expanding lesion in or around the cavernous sinus, most often a meningioma, schwannoma or carotid aneurysm.^1,2 Aberrant regeneration is rare after microvascular palsies, so its presence without a history of trauma should raise suspicion of a compressive lesion.²