IIIrd Cranial Nerve Lesion

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IIIrd Cranial Nerve Lesion

IIIrd Cranial Nerve

  • loss of motor to most of eye movements and parasympathetic supply to pupil

  • All muscles paralysed except lateral rectus and superior oblique
  • Eye points down and out

  • Pupillary fibres run on outside of 3rd nerve

  • Pupillary-sparing lesion is likely to be ischaemic
  • Pupillary-involving is likely to be compressive → More dangerous

Examination

  • General

    • Ptosis

  • Acuity

    • normal

  • Fields

    • normal (limited by ptosis)

  • Pupil

    • dilated

    • no reaction if complete lesion

  • Movements

    • VIth intact

      • eye moves laterally

    • IVth intact

      • eyes intorts (???) on trying to look down and in

  • Fundi

Causes

Solitary

  • idiopathic

  • dilatation of pupil
    • raised ICP → uncal herniation through tentorium
    • aneurysm of ipsilateral posterior communicating artery (PCA)
    • Tumour
  • without dilated pupil
    • Diabetes Mellitus
    • nerve trunk infarct
    • midbrain lesion
      • vascular
      • demyelination
    • giant cell arteritis
    • syphilis

Smallprint

  • encephalitis
  • meningiomas
    • parasellar
    • sphenoidal wing

WIth IV and VI

  • stroke
  • tumours
  • Wernicke's encephalopathy
  • aneurysms
  • MS
  • myasthenia gravis
  • muscular dystrophy
  • myotonic dystrophy
  • cavernous sinus thrombosis

Investigations

  • blood glucose
  • CT / MRI
  • carotid arteriography
 

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