Bilateral traumatic avulsion of abducens nerve

Avulsão traumática bilateral do nervo abducente

LETTERS

Bilateral traumatic avulsion of abducens nerve

Avulsão traumática bilateral do nervo abducente

Bruno S.C. Lopes^I; Lazaro L.F. do Amaral^I; Higor G. Bezerra^I; Ricardo M. Rogério^I; Antônio A. Zambon^II

^IDepartment of Neuroradiology, Medimagem, Hospital Beneficência Portuguesa e Hospital Santa Catarina, São Paulo SP, Brazil

^IIDepartment of Neurology, Hospital A.C. Camargo, São Paulo SP, Brazil

^{Correspondence}

A 45-year-old previously healthy woman suffered a head trauma with neck hyperextension during bike exercise, losing consciousness for about 24 hours. Upon awakening, she presented bilateral lateral gaze palsy and convergent strabismus (Fig 1). No bone fracture was detected on CT studies (not shown). This clinical picture persisted unchanged for over one year and a MRI study done at our service showed bilateral avulsion of the sixth cranial nerve using FIESTA sequence (Fig 2A, B, C and D).

The abducens innervates the lateral rectus muscle, which is responsible for the horizontal lateral movement of the ocular globe. It has a long course, beginning at its nucleus, on the ventral pons, going through the pre-pontine cistern to its dural entry point on the petroclival region, coursing through Dorello's canal, beneath petroesphenoidal ligament, where it is covered by an envelope composed of one dural layer and one arachnoidal layer¹ to the cavernous sinus, lateral to the internal carotid artery, reaching the superior orbital fissure and orbital apex. This long course makes it more susceptible to injuries.

Various different diseases can cause sixth nerve palsy, neoplasic and traumatic etiologies being more common in children, while vascular and idiopathic are responsible for the majority of cases in adult population².

Traumatic injuries of abducens nerve are a well-known consequence of severe head trauma, reported in 1-2,7% of the cases, with or without associated cervical or skull base fracture³. Usually, the mechanism of injury is contusion/stretching along its course and vertical displacement (downward and/or upward) of the brain is supposed to be the cause of these lesions⁴. Two points along the nerve course are described as the most prone to injury^3-5: the dural entry point (during upward displacement) and the petrous apex (during downward displacement). Since these two movements are usually associated on severe head trauma, these two points likely work together to cause the lesion.

In our case, with a MRI study acquired on 1.5 tesla equipment (GE Medical systems - Milwaukee), using FIESTA sequence post processed in dedicated workstation, we observed bilateral sixth nerve discontinuity along its pre-pontine course, detached from the pons, at the pontmedullary sulcus level. The other cranial nerves had preserved morphology. There were no signs of bone fracture, brainstem or orbital muscle lesions.

FIESTA (different names are used for similar technique by other manufacturers, like BALANCED FFE and 3D-CISS, for example) is a magnetic resonance sequence heavily T2-weighted, capable of acquiring very thin slices, allowing reformation in all three planes, optimal for analyzing morphologic features of structures next to CSF containing spaces, like basal cisterns.

In the presented case, one year after trauma, there was still unchanged ophthalmoplegia and a MRI study showed bilateral complete abducens nerve avulsion. As far as we know, no previous report has showed, with imaging studies, this consequence of head trauma.

Received 1 March 2011

Received in final form 28 March 2011

Accepted 13 April 2011

• 1. Kenichiro O, Arai H, Endo T, et al. Detailed MR imaging anatomy of the abducent nerve: evagination of CSF into Dorello canal. AJNR Am J Neuroradiol 2004;25:623-626.
• 2. Berlit P, Reinhardt-Eckstein J, Krause KH, et al. Isolated abducens paralysis: a retrospective study of 165 patients. Fortschr Neurol Psychiatr 1989; 57:32-40.
• 3. Arias MJ. Bilateral traumatic abducens nerve palsy without skull fracture and with cervical spine fracture: case report and review of the literature. Neurosurgery 1985;16:232-234.
• 4. Hollis G. Sixth cranial nerve palsy following closed head injury in a child. J Accid Emerg Med 1997;4:172-175.
• 5. Advani RM, Baumann MR. Bilateral sixth nerve palsy after head trauma. Ann Emerg Med 2003;41:27-31.

Publication Dates

• Publication in this collection
  01 Sept 2011
• Date of issue
  Aug 2011