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[Post-traumatic anomalous innervation of the lateral rectus muscle by trigeminal fibers].

BACKGROUND
Congenital or acquired anomalous synkinetic movements are common in Neuro-Ophthalmology. Examples are the Stilling-Türk-Duane syndrome, the Marcus Gunn phenomenon or secondary oculomotor synkinesis in oculomotor nerve palsy.


PATIENT AND METHOD
A 29-year-old woman with N.V-, N.VI-, N.VII- and N.VIII-lesion after blunt cranio-cerebral trauma developed a left sided trigemino-abducens synkinesis. The abduction of the left eye by gaze effort was limited to 30 degrees before the midline. With tight jaw closure the eye reached the midline. Eye muscle surgery was performed (recess-resect procedure) because of homonymous diplopia. This is the third published case of a posttraumatic trigemino-abducens synkinesis.


RESULTS
Postoperatively the left globe was able to abduct 20 degrees over the midline using maximum coinnervation, with a left exotropia of 5 degrees. Without coinnervation, i.e., without jaw closure an residual esotropia of 26 degrees at distance and 14 degrees at near remained. The utilization of the synkinesis to compensate the esodeviation and to avoid diplopia was hardly possible even after a combined operation for esotropia. It is difficult to determine the amount and type of surgery since one has to take into account that the coinnervation produces an abduction of the eye depending on the intensity of jaw closure.


DISCUSSION
The trigemino-abducens synkinesis may be explained by aberrant regeneration of the peripheral never at the temporal petrous bone. Here, aberrant regrowing fibres of the mandibular nerve destined for the masseter muscle may reach the lateral rectus muscle via adjacent distal sheaths of the degenerated proprioceptive fibres of the lateral rectus muscle. Other mechanisms (ephaptic transmission or central reorganisation between the N.V- and N.VI-nuclei in the brain stem) are very unlikely.