Disorders Of Smell

OLFACTORY (I) cranial nerve conveys the sensation of smell.

^ Olfactory bulb

^ Olfactory bulb

A number of fine nerves arising from receptor cells in the nasal mucosa pierce the cribriform plate of the ethmoid bone. These pass to the olfactory bulb where they synapse with neurons of the olfactory tract.

Undersurface of frontal lobe

The axons partially decussate as they pass back in the olfactory tract to the piriform area of the temporal lobe and the amygdaloid nucleus.

Optic -chiasma~^

Piriform area i


Optic -chiasma~^


Olfactory bulb

^ Olfactory tract

Piriform area i

Mamillary bodies

IMPAIRMENT or LOSS OF _| SMELL (anosmia) - unilateral or bilateral

Differential diagnosis

TEMPORARY- Upper respiratory tract infection: inflammation of the nasal mucosa is the commonest cause of impairment or loss of smell.

Head injury: anosmia may occur with or without evidence of cribriform plate fracture. Recovery is usual.

Viral infections'. any viral illness may cause anosmia which can be permanent

Drugs: penicillamine -Endocrine disease: Addison's disease and thyrotoxicosis Tumours: Olfactory groove meningioma Frontal bone osteoma Pituitary tumours Frontal lobe glioma Frontal lobe abscess

Aneurysm of the circle of Willis: Anterior communicating,


L Raised intracranial pressure: without local damage to olfactory structures, may rarely cause anosmia

- Ipsilateral anosmia

- Ipsilateral optic atrophy - occurs with olfactory groove

- Contralateral papilledema or sphenoid ridge masses




occur in complex partial seizures and migraine

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