Lesions of the abducens nerve (CN VI)
Lesions of the abducens nerve (CN VI)
Features of a Abducens (Sixths) Nerve Palsy
Expected features
- Failure to abduct the affected eye
Causes of a unilateral lesion:
- Head injury (most common) with BOSF
- Raised intracranial pressure
- Localising lesion.... at any number of levels:
- Damage to the frontal eye field of the frontal lobe, which occupies some of the middle frontal gyrus
- Damage to the posterior hemispheres, which would be accompanied by a hemianopia
- Brainstem (tumour, stroke) - the paramedian prepontine reticular formation mentioned in this question, which receives information from higher cortical centres and transmits them to the abducens nucleus.
- Petrous portion of temporal bone (otitis media-associated osteomyelitis, mastoiditis)
- Clivus (intraforaminal extension of nasopharyngeal carcinoma or similar)
- Cavernous sinus (thrombosis)
- Superior orbital fissue (base of skull fracture)
- Any damn where (basal forms of meningitis, eg sarcoidosis, tuberculosis, cryptococcus)
Causes of a bilateral lesion
These are freakishly rare.
- Wernicke's encephalopathy is the most common cause of this
- Diabetes-associated neuropathy
- Myasthenia gravis
- Generally speaking, polyneuropathies such as Guillain-Barre
- Massively raised intracranial pressure
References
The LITFL summary of cranial nerve lesions is without peer in terms of useful information density.
Walker, H. Kenneth, W. Dallas Hall, and J. Willis Hurst. "Clinical methods." 3rd edition.(1990).Chapter 60 Cranial Nerves III, IV, and VI: The Oculomotor, Trochlear, and Abducens Nerves - by J. Donald Fite and H. Kenneth Walker.
Twenty five years out of date, but still relevant.
These authors, in turn, reference even more ancient vellum:
Leigh RJ, Zee DS. The neurology of eye movements. Philadelphia: FA Davis, 1983.
Miller NR. Walsh and Hoyt's clinical neuro-ophthalmology. Vol 2. 4th ed. Baltimore: Williams and Wilkins, 1985.