ANNALS or ANATOMY

Synkinesis between facial nerve and oculomotornerve. A case report

Cornelius Lemke* and Ihab EI Bably

*lnst itute of Ana tomy I and Clinic of Ophthalmology, Friedr ich Schiller University,Teichgraben 7, D-07743 lena, Germ any

Summary. We present a case history of a young man suf­fering from a facial-oculomotor synkinesis. The findingsspea k in favour of an aquire d synkinesis due to traum a.Most probably the injury occurre d in the midbrain , in thearea of the vertical gaze control center and /or the area ofthe levator palpebrae motoneurons. A congenital syn­kinesis due to emb ryonic malformation seems to be un­likely, because at birth no restri ction of the eye-ballmotility was present.

Key words: Synk inesis - Facial ner ve - Oculomotor nerve

Introduction

The term synkinesis means unconscious co-movementsof a single muscle or a group of muscles during con­scious contraction of designated muscles (associ atedmovements). One can distinguish between acquired andcongenital forms of synkineses. Acquired synkineses de­velop because of false regenerat ion after trauma or inthe presence of a tumor. In the mod ern view synkinesismay develop from ephaptic neuronal transmission , thatis to say, an unph ysiological contact of nerve fibers atthe site of nerve injur y with an increased transfer of thenerve excitation. Moreover , synkines is can be developedfrom synaptic reorganizat ion of retrogradely affectedneurons (Schmidtke and Buttner-Ennever 1992). Conge­nital synkineses arise durin g false regeneration aftercongenital diseases, or are a result of embryonic malfor­mation .

The most common congenita l synkines is is the mand i­bulo-palpebral phenomenon first described by Marcus

Corres pondence to : C. Lemke

G unn (1883). This synkinesis is characterized by a conge­nital ptosi s, which become s weaker during movem ent ofthe mandible to the cont ralateral side or dur ing its pro­tru sion . A synkines is exists between the oculomotornerve, responsible for the innervation of the levator pal­pebrae muscle, and the trigeminal ner ve (later al pter­ygoid nerve ), responsible for the innervation of thelater al pterygoid muscle (trigemino-oculomotor synkin­esis) (Eve 1987).

An inverse Marcus Gunn phenomenon has been de­scribed by Marin Am at (1919). The term was chosen be­cause the movement of the eye is exactly opposi te towhat happens during the Marcus Gunn phenomenon, i .e.,sinking of the lid dur ing opening of the mouth. Thepathogenesis of the inve rse Marcus Gunn phenomenon isdifferent from that of the Marcus Gunn phenomenon(Rana and Wadia 1985). In the Marin Amat syndrome asynkinesis has form ed between the trigeminal nerve,which innervates the lateral pterygoid muscle and the fa­cial nerve, which innervates the orbicularis oculi muscle(trigemino-facial synkin esis).

In the literature we found a case report of a hypoglos­sal-accessory-oculomoto r-synkinesis (Pe rry 1957). Theptosis of the upper lid impr oved during contraction of thesterno cleidomastoid muscle or protrusion of the tongue.

In another case, an abducent-oculomotor synkin esis oc­curred in conn ection with a congenital paresis of the ab­duc ent nerve (Duke-Elder 1964).

However , anoth er form of synkines is, the facial-oculo­motor synkinesis, is very rare. Brandley described a pa­tient with imp rovement of the pto sis during smiling(Bra dley and Toone 1967). Kirkh am men tioned a simi larcase (Kirkham 1971).

In the article present ed here we demonstrate a case ofa patient with a facial-oculomotor synkinesis. Moreover,we have attempted to localize the dam age to the neuronsresponsible for this synkinesis.

Ann Anat (1998) 180: 339-3 42© Gustav Fisch er Verl ag

Case report

A 28-year-old male patient was examined at the Strabis­mus Lid Surgery Service of the University Eye Hospitalin lena.

At the age of four years the patient was in a car acci­dent . He was admitted to the Neurosurgical Clinic of theUniversity of Leipzig in a coma. There, an osteoclastictrepanation was performed.

Postoperatively, an oculomotor palsy of the left sideand a contralateral hemiplegia developed. No other cra­nial nerves were involved. At the age of 13, a ptosis op­eration by resection of the levator palpebrae muscle wasperformed. The operation was not successful.

The latest ophthalmic examination revealed the follow­ing findings: First: Visual acuity in the right eye was com­plete, in the left eye it was reduced to 1/10. On both sidesthe pupillary light reflex was brisk. The anterior segmentsof the bulbs and the fundi showed no abnormalities. Sec­ond: there was a 20 degrees low of the left bulb with alimited elevation in the upgaze due to palsy of the rectussuperior muscle. Adduction, abduction and depression ofthe left eye were not restricted .

Third: in addition to the palsy of the left rectus super­ior muscle there was also a disturbance of the innervationof the levator palpebrae muscle with a strong ptosis onthe left side (Fig. 1). A unilateral elevation of the ptoticeyelid appeared with the contraction of the platysma(Fig. 2). During masticatory movements no elevation ofthe eyelid could be seen. Therefore , a Marcus Gunn phe­nomen can be excluded. The co-movement of the ptoticleft eye with the contraction of the platysma suggests thepresence of a oculomotor-facial synkinesis.

Discussion

A traumatic etiology of a synkinesis can be explainedthrough false sprouting of nerve fibers after paresis (UI­lerich 1978). In the case presented here, nerval impulsesto muscles normally innervated by the facial nerve are ac­companied by contraction of muscles usually innervatedby the oculomotor nerve. Incidentally, a palsy (disturb­ance) of the facial nerve was been diagnosed, only a palsyof the oculomotor nerve was not found.

Fig. 1. A 28-year-old man with a ptosis of the left eyelid. Fig. 2. Contraction of the platysma evokes an elevation of theeyelid. The bulb is turned downward.

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To locate the damage it was necessary to analyse thetopographic relationship of both nerves and their motoricnuclei.

The motoric neurons of the IIIrd cranial nerve origi­nate from the midbrain at the level of the superior colli­culi, ventral to the cerebral aqueduct, in the area of theperiaqueductal gray matter. The neurons of the extraocu­lar muscles are arranged bilaterally in longitudinalgroups. Only one unpaired nucleus, the central caudalnucleus (CCN), supplies the levator palpebrae superiormuscle of both sides (Barr and Kiernan 1983). The CCNis an integral part of the oculomotor nucleus. Motoneur­ons of the levator palpebrae muscle and the rectus super­ior muscle lie close together (Miyazaki 1985). In lateontogenesis, the levator palpebrae muscle separates fromthe superior rectus muscle (Gilbert 1957). This explainsthe possibility of simultaneous failure of both muscles.

Myelinated axons leave the oculomotor nuclei and passventral to the interpeduncular fossa, thereby crossing thered nucleus. The fibres reach the orbit through the supe­rior orbital fissure.

The nuclei of origin of the facial nerve lie in the teg­mentum rhombencephali, the motoneurons innervatingthe platysma lying ventrally (Holstege 1996). The fibrebundles of the motor neurons loop over the abducent nu­cleus, reaching the surface of the brain in the angle be­tween pons and cerebellum. During their infranuclearintracranial course, no direct connections between fibresof the oculomotor nerve and the facial nerve are knownto exist.

Also, during the extracranial course there is no closerelationship between fibres of the IIIrd and VIIth cranialnerves.

Direct projections from the neocortex to the motor nu­clei of the IIIrd cranial nerve are also unknown. It is pos­sible that only gaze control centers project to the nucleiof origin (Nauta and Feirtag 1990). The premotor neu­rons for the horizontal gaze (horizontal gaze control cen­ter) lie in the caudal pontine medial tegmentum, alsoreferred to as the paramedian pontine reticular formation(PPRF) (Biittner-Ennever et a1. 1982). It controls trunkand neck muscles, as well as the extrinsic eye-muscle mo­toneurons in the abducent nucleus. From there, inter­neurons activate medial rectus motoneurons in thecontralateral oculomotor nucleus to bring about conju­gated horizontal eye movements (Holstege 1996). Thevertical gaze control center is located more rostrally inthe tegmentum. One may conclude that vertical eye andhead movements develop late in phylogeny (Holstege1996). Important nuclei are the interstitial nucleus of Ca­jal and the rostral interstitial nucleus of the medial longi­tudinal fasciculus (riMLF) (Holstege 1996). Theinterstitial nucleus of Cajal has direct premotor control ofvertical extraocular motoneurons (Biittner-Ennever andBiittner 1988). The riMLF is responsible for rapid eyemovements with a vertical and/or torsional component(Suzuki et a1. 1995; Riordan-Eva et a1. 1996). Moreover,the riMLF is involved in the control of coordinated lid

movements during vertical movements of the bulbus. Theunpaired levator palpebrae motor nucleus is controlledby premotor motoneurons, which bring about lateraliza­tion (Schmidtke and Buttner-Ennever 1992).

The gaze control centers again receive projections fromthe Areas 19, 22 and 8. However, no part of the neocor­tex can be declared as "oculomotor cortex", because thecontrol of ocular movements may be distributed acrosswide areas of the cortex (Nauta and Feirtag 1990).

Recently, Biittner-Ennever et a1. (1996) demonstratedpatients suffering from similar symptoms as our patient.There, ptosis and downgaze paralysis occurred because ofdamage in the area of the levator palpebrae motoneu­rons, rostral interstitial nucleus of the MLF (riMLF), andcells in the mesencephalic midline.

We suggest that in our case, regions of the midbrain ofthe patient were damaged by the trauma which gave riseto the ptosis and upgaze paralysis. Synkinesis with fibersof the facial nerve could also develop in this region. Sincethe motor nuclei of the seventh cranial nerve lie morecaudal, nerve sprouts would emerge above the nucleus.

Conclusion

Summarising the findings in this patient, we assume thatthe synkinesis developed in the region of the midbrainafter trauma. A congenital cause of the synkinesis seemsto be less probable, since at birth no restrictions of theeyeball motility had been diagnosed.

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Accepted February 20,1998

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