Bilateral duplication of the abducens nerve - case study.

The abducens nerve is characterized by a long intracranial course and complex topographical relationships. Anatomical knowledge may help to understand both the etiology and clinical symptoms of abducens nerve palsy. Typically, the single trunk of the abducens nerve travels on both sides. However, occasionally different variants of unilateral or bilateral duplications of the abducens nerve may be observed. The presented paper is a detailed anatomical description of bilateral duplication of the abducens nerve, with atypical appearance of the nerve in the cavernous sinus and normal distribution within the lateral rectus muscle on both sides of one cadaver. On the right side both trunks of the abducens nerve fused within the subarachnoid space and pierced the dura mater together. On the left side both trunks of the duplicated abducens nerve pierced the dura mater separately, entered the petrous apex separately and fused just below the petrosphenoidal ligament. Within the cavernous sinus the nerve divided once again into two filaments, which reunited into one trunk a er crossing the horizontal segment of the intracavernous part of internal carotid artery. The orbital segments of the abducens nerve showed a typical course on both sides. Duplication of the abducens nerve is anatomical variation which should be taken into account during diagnostic and surgical procedures performed within the petroclival region and cavernous sinus.

Postoperative full abduction in a patient of Duane retraction syndrome without an abducens nerve: a case report.

BACKGROUND: Duane retraction syndrome (DRS) consists of abduction deficit, globe retraction and upshoots or downshoots with adduction. The abducens nerve on the affected side is absent in type 1 DRS. After bilateral medial rectus muscle recession in unilateral type 1 DRS may improve the abduction limitation, but still more than -3 limitation remains. CASE PRESENTATION: A 6-month-old boy presented with esotropia which had been noticed in early infancy. He showed limited abduction, fissure narrowing on attempted adduction and a small upshoot OS. Left abducens nerve was not identified on magnetic resonance imaging compatible with Duane retraction syndrome type 1. He showed full abduction after bilateral medial rectus recession of 6.0 mm at the age of 9 months, and remained orthotropia with full abduction OU 2 years postoperatively. He is my only patient with Duane retraction syndrome who showed full abduction after bilateral medial rectus recession. CONCLUSIONS: A patient with the type 1 Duane retraction syndrome rarely may show full abduction after bilateral medial rectus recession mimicking infantile esotropia.

An unusual variant of the abducens nerve duplication with two nerve trunks merging within the orbit: a case report with comments on developmental background.

This study reports the first case of abducens nerve duplication along its entire intracranial course, ending within the orbit. A distinct abducens nerve duplication reaching the common tendinous ring (annulus of Zinn), as well as another split within the intraconal segment of the nerve have been revealed. Additionally, two groups (superior and inferior) of abducens nerve sub-branches to the lateral rectus muscle were visualised using Sihler's stain. The analysed anatomical variation has never been reported before and it seems to be in the middle of the spectrum between the cases of duplication occurring only within the intracranial segments of the abducens nerve found in the literature and those continuing throughout the whole course of the nerve. Abducens nerve duplication may be treated as a relic of early stages of ontogenesis. Such a variant might result from alternative developmental pathways in which axons of the abducens nerve, specific for a given segment of the lateral rectus muscle, run separately at some stage, instead of forming a single stem.

Magnetic resonance imaging in congenital Brown syndrome.

AIMS: Our aim was to elucidate the etiology of Brown syndrome by evaluating the trochlea position, morphologic characteristics of the extraocular muscles including superior oblique muscle/tendon complex, and the presence of the cranial nerves (CN) III, IV, and VI using magnetic resonance imaging (MRI) in eight patients with unilateral congenital Brown syndrome and one patient with bilateral congenital Brown syndrome. METHODS: Nine consecutive patients diagnosed with congenital Brown syndrome had a comprehensive ocular examination and MRI for the CN III, CN VI, and the extraocular muscles. Five of the nine patients underwent additional high resolution MRI for CN IV. The distance from the annulus of Zinn to the trochlea was measured. RESULTS: Normal sized CN III, IV, and VI, as well as all extraocular muscles, could be identified bilaterally in all patients with available MRI. The distance from the annulus of Zinn to the trochlea was the same in both eyes. CONCLUSIONS: The findings for our patients, particularly in those who underwent additional high resolution MRI, did not provide evidence of a lack of CN IV as a cause of Brown syndrome.

MRI findings in Duane's ocular retraction syndrome.

AIM: To investigate the innervation pattern of extra-ocular muscles in patients with clinically diagnosed Duane's ocular retraction syndrome (DRS) using magnetic resonance imaging (MRI). MATERIALS AND METHODS: The study population consisted of 11 patients. Six patients had type I DRS (eight eyes), four patients had type II DRS (five eyes) and one patient had inverse DRS. Images were acquired using a Siemens 3 T MRI system. The type of DRS, corresponding innervation findings, and condition of the affected muscles were evaluated by two experienced neuroradiologists in consensus. RESULTS: All patients with clinically diagnosed DRS type I showed absence of the abducens nerve (CN6), hypoplasia of the superior oblique muscle (SOM), and aberrant innervation of lateral rectus muscle (LRM) by an extra branch of oculomotor nerve (CN3). All patients with type II DRS show dual-innervation of the LRM (by CN6 and an aberrant CN3 branch) and hypoplasia of SOM. The single patient with inverse DRS showed hypoplasia of CN3, the medial rectus muscle (MRM), the inferior rectus muscle (IRM), and the inferior oblique muscle (IOM). CONCLUSION: Each type of DRS has characteristic MRI appearances. Therefore, MRI is a useful diagnostic tool for the confirmation and classification of suspected cases of DRS.

Trigemino-abducens synkinesis after lateral orbitotomy.

A 30-year-old man underwent lateral orbitotomy with removal of dermoid cyst in the right orbit. One month after operation, the patient started to experience double vision. He had 25 prism diopters of esotropia in primary gaze with marked limitation of abduction in the right eye. Seven months after the operation, he developed synkinetic movement of the eye when clenching his teeth. He could abduct his right eye while gritting his teeth. This is the fourth reported case of trigemino-abducens synkinesis and the first reported case without brain trauma.

Aberrant Abducent Nerve During Microvascular Decompression for Trigeminal Neuralgiass.

BACKGROUND: Microvascular decompression (MVD) is a commonly performed procedure to treat trigeminal neuralgia and hemifacial spasm. Knowledge of the variable anatomy of the cerebellopontine angle is crucial to avoid injury to cranial nerves. CASE DESCRIPTION: A 76-year-old lady with right V1 (ophthalmic division of the trigeminal nerve) and V2 (maxillary division of the trigeminal nerve) trigeminal neuralgia, refractory to medical treatment, underwent elective MVD. Intraoperatively, a distorted course of the cisternal component of the abducent nerve was noticed, caused by an ectatic anterior inferior cerebellar artery. Careful mobilization of the offending vessel to decompress the trigeminal nerve was carried out; however, abducent nerve decompression was not attempted since its function was not compromised. Facial pain resolved postoperatively without new diplopia. CONCLUSIONS: Careful review of imaging before surgery is recommended in order to preempt such unusual anatomic variations.

Variable synergistic divergence.

PURPOSE: To report a patient with congenital fibrosis of the extraocular muscles showing either synergistic divergence or adduction. CASE REPORT: A 7-year-old girl presented with complaints of abnormal eye movement since early childhood. A detailed ophthalmologic examination was performed. On ophthalmologic evaluation, her corrected visual acuities were 20/50 OU. She had 12 prism diopters of exotropia at distance and near in the primary position. During attempted right gaze, OU abducted. During attempted left gaze, the right eye adducted or abducted. Upgaze and downgaze were limited. Levator function was evaluated at 0 mm with a marginal reflex distance of -1 in OU. On thin-section brain stem magnetic resonance imaging, the left abducens nerve was absent, and the right and left oculomotor nerves were severely hypoplastic. The oculomotor nerve was smaller than the acoustic nerve was, and this was interpreted as hypoplasia according to a previous method (Kim and Hwang, Ophthalmology 2005;112:728-32). The medial and superior recti of OU were atrophic. CONCLUSIONS: A patient with congenital fibrosis of the extraocular muscles may show alternatively either synergistic divergence or adduction, which has not been documented before.

Pediatric strabismus imaging.

PURPOSE OF REVIEW: With both radiologists and ophthalmologists in mind, this article describes the best use of computed tomography and magnetic resonance imaging in the diagnosis of strabismus. RECENT FINDINGS: Both computed tomography and magnetic resonance imaging are valuable tools in evaluation of strabismus, despite concerns about radiation exposure with computed tomography. Advancements in magnetic resonance imaging are being made and open new techniques that can be useful in the future evaluation of strabismus. SUMMARY: Computed tomography and magnetic resonance imaging are safe tools in the evaluation of certain types of pediatric strabismus. The collaboration between imagers and ophthalmologists is essential in the development of feasible innovative methods of imaging that will advance diagnosis and monitoring in children with strabismus.

Supernumerary Abducens Nerves: A Comprehensive Review.

BACKGROUND: Branching and/or replication of the abducens nerve is not an uncommon occurrence. Although numerous variations have been documented, the rarest forms are duplicated or triplicated nerves, where multiple nerve roots originate from the brainstem, travel intracranially, and attach to the lateral rectus as separate entities. METHODS: We conducted a systematic literature search on the topic of supernumerary abducens nerve, using PubMed and Google Scholar. RESULTS: After screening, 16 studies were included: 11 cadaveric studies and 6 case reports. CONCLUSIONS: In this paper, we review the literature on variations found, discuss current hypotheses and clinical relevance, and propose future studies. Neurosurgeons should be aware of such nerve variants when viewing imaging or operating in the regions traversed by the abducens nerve.

Bilateral incyclotorsion, absent facial nerve, and anotia: fellow travelers in Möbius sequence or oculoauriculovertebral spectrum?

We report a patient with bilateral incyclotorsion, asymmetric facial palsy, monocular depression deficiency, and unilateral Type 3 Duane syndrome, along with contralateral anotia and a midline cleft palate. A dysplastic middle ear cavity and unilateral absence of the facial nerve were noted on magnetic resonance imaging scanning. The differential diagnosis includes Möbius sequence, oculoauriculovertebral spectrum, and a congenital cranial dysinnervation disorder.

Cervico-oculo-Acoustic syndrome in a male with consanguineous parents.

BACKGROUND: The cervico-oculo-acoustic syndrome comprises Klippel-Feil anomaly, sensorineural deafness and Duane's retraction syndrome. Polygenic, autosomal dominant, and X-linked inheritance have been hypothesized. The disorder has rarely been reported in males. CASE REPORT: A 42-year-old male, born of consanguineous parents, presented with Duane's syndrome, mixed hearing loss, C2-C3 fusion, neck stiffness, and right facial palsy. A variety of cardiac, neurological and urogenital anomalies occurred in his relatives. The electro-oculographic studies showed impaired abduction and adduction of the right eye and impaired abduction of the left eye. Vergence, vertical eye movements and peripheral vestibular responses were normal. Somatosensory evoked potentials showed absence of the N13 peak and brainstem auditory evoked potentials bilateral delay of the I-III interpeak latencies. CONCLUSIONS: Consanguinity of the patient's parents, not previously reported, suggests autosomal recessive inheritance, but autosomal dominant inheritance is indicated by the family history. The pattern of the oculomotor deficit is consistent with bilateral dysplasia of the abducens nuclei with preserved internuclear neurons in the right abducens nucleus. Neurophysiological investigations revealed lower brainstem and cervical cord involvement.

Abducens-oculomotor synkinesis associated with internuclear ophthalmoplegia and acquired abducens nerve palsy.

We report a case of acquired abducens-oculomotor synkinesis, internuclear ophthalmoplegia, and abducens nerve palsy following brainstem hemorrhage. Weakening surgery on the medial rectus muscle did not eliminate the synergistic movement. The mechanism responsible for the abducens-oculomotor synkinesis is discussed.

Hypoplastic oculomotor nerve and absent abducens nerve in congenital fibrosis syndrome and synergistic divergence with magnetic resonance imaging.

OBJECTIVE: There is only one neuropathologic report of congenital fibrosis of the extraocular muscles (CFEOM), and none of synergistic divergence. The aim of this report was to study the oculomotor nerve and the abducens nerve in 2 such patients with magnetic resonance imaging. DESIGN: Observational case reports. METHODS: Ophthalmologic examination and thin-sectioned magnetic resonance imaging across the brainstem level were performed in 2 patients with CFEOM and synergistic divergence. To confirm the accuracy of the procedure, we compared the results obtained with those of a control group of 40 individuals using the same technique. MAIN OUTCOME MEASURES: The oculomotor nerve and the abducens nerve on magnetic resonance imaging. RESULTS: Magnetic resonance imaging disclosed bilateral hypoplasia of the oculomotor nerve in both patients, and absence of the abducens nerve on the affected side of synergistic divergence. The oculomotor and abducens nerves were observed in 80 of 80 eyes (100%) screened as controls. CONCLUSIONS: In both patients with CFEOM and synergistic divergence, the oculomotor nerve was hypoplastic bilaterally, and the abducens nerve was absent on the side exhibiting synergistic divergence.

Normal abduction in a patient with duplicated abducens nerve.

PURPOSE: To our knowledge, there has been no report of ophthalmologic findings related with a duplicated abducens nerve in the ophthalmic literature. This study reports such findings. METHODS: An ophthalmologic examination was performed in one patient with a duplicated abducens nerve, revealed with thin-sectioned magnetic resonance imaging (MRI) across the brainstem level. RESULTS: The MRI disclosed a duplicated left abducens nerve. The patient was orthotropic in five cardinal positions, and her ductions and versions were full. CONCLUSIONS: One patient with a duplicated abducens nerve showed orthotropia and normal ocular movement.

Bilateral duplication of the abducens nerves: an incidental finding on magnetic resonance imaging.

Although anomaly of the abducens nerve, including duplication, has been reported in anatomical papers, no radiological report exists regarding a duplicated abducens nerve observed on magnetic resonance (MR) imaging. We encountered a case of bilateral duplication of the abducens nerves, which was found incidentally on MR scans from an 11-year-old boy. He did not have any symptoms of eye movement related to abducens nerve abnormality; thus, the duplication was considered to be a normal variant in this patient. Radiologists should be aware that duplication of the abducens nerve may occur and can be diagnosed on MR, particularly when diagnosing symptomatic patients or as a preoperative assessment for microsurgery of the nerve.