Cranial nerve I palsy

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