cranial nerve I palsy

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A change in smell sensation due to a olfactory nerve palsy can be uni- or bilateral in nature. Lesions are most likely to cause anosmia and a bilateral lesion is more likely to be detected by routine enquiries about an individual's sense of smell.

Most causes of anosmia are bilateral.

Causes of bilateral anosmia include:

  • upper respiratory tract infection - most common
  • ethmoid tumour
  • meningioma of the olfactory groove
  • trauma, e.g. basal skull fracture, frontal fracture, after pituitary surgery
  • congenital, e.g. Kallman's syndrome
  • conductive, e.g. nasal polyps, enlarged turbinates

Causes of unilateral anosmia include:

  • head trauma without a fracture
  • early meningioma of the olfactory groove

Last reviewed 01/2018

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