title: Nonaneurysmal cranial nerve compression as cause of neuropathic strabismus: evidence from high-resolution magnetic resonance imaging.
abstract: OBJECTIVE
  To seek evidence of neurovascular compression of motor cranial nerves (CNs) in otherwise idiopathic neuropathic strabismus using high-resolution magnetic resonance imaging (MRI).
  
  
  METHODS
  Prospective, observational case series.
  
  
  METHODS
  High-resolution, surface coil orbital MRI was performed in 10 strabismic patients with idiopathic oculomotor (CN III) or abducens (CN VI) palsy. Relationships between CNs and intracranial arteries were demonstrated by 0.8-mm thick, 162-μm resolution, heavily T2-weighted MRI in fast imaging using steady-state acquisition sequences. Images were analyzed digitally to evaluate cross-sectional areas of extraocular muscles.
  
  
  RESULTS
  In one patient with CN III palsy, an ectatic posterior communicating artery markedly flattened and thinned the ipsilateral subarachnoid CN III. Cross-sections of the affected medial, superior, and inferior rectus muscles 10 mm posterior to the globe-optic nerve junction were 17.2 ± 2.5 mm(2), 15.5 ± 1.3 mm(2), and 9.9 ± 0.8 mm(2), significantly smaller than the values of 23.6 ± 1.9 mm(2), 30.4 ± 4.1 mm(2), and 28.8 ± 4.6 mm(2), respectively, of the unaffected side (P < .001). In 2 patients with otherwise unexplained CN VI palsy, ectatic basilar arteries contacted CN VI. Mean cross-sections of affected lateral rectus muscles were 24.0 ± 2.3 mm(2) and 29.8 ± 3.1 mm(2), significantly smaller than the values of 33.5 ± 4.1 mm(2) and 36.9 ± 1.6 mm(2), respectively, in unaffected contralateral eyes (P < .05).
  
  
  CONCLUSIONS
  Nonaneurysmal motor CN compression should be considered as a cause of CN III and CN VI paresis with neurogenic muscle atrophy when MRI demonstrates vascular distortion of the involved CN. Demonstration of a benign vascular cause can terminate continuing diagnostic investigations and can expedite rational management of the strabismus.
authors.affiliation: Jules Stein Eye Institute, University of California, Los Angeles, USA.
authors.forename: Tzu-Hsun
authors.initials: TH
authors.lastname: Tsai
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Demer
mesh_terms: D020434:Abducens Nerve Diseases / Q000175:diagnosis / Q000209:etiology*; D000293:Adolescent; D000328:Adult; D002539:Cerebral Arterial Diseases / Q000150:complications*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D002532:Intracranial Aneurysm / Q000473:pathology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009408:Nerve Compression Syndromes / Q000150:complications*; D009801:Oculomotor Muscles / Q000473:pathology; D015840:Oculomotor Nerve Diseases / Q000175:diagnosis / Q000209:etiology*; D011446:Prospective Studies; D013285:Strabismus / Q000209:etiology*; D013346:Subarachnoid Space; D055815:Young Adult