A 24-year-old man develops complete loss of smell after a motorbike accident in which he struck the back of his head. He has no other neurological deficit. The most likely anatomical basis of his anosmia is:

• A Contusion of the olfactory bulbs against the frontal lobes alone
• B Injury to the trigeminal nerve endings in the nasal mucosa
• C Damage to the uncus of the temporal lobe
• D Shearing of olfactory nerve filaments as they traverse the cribriform plate ✓

Explanation

The unmyelinated axons of olfactory receptor neurons pass through foramina of the cribriform plate of the ethmoid bone to reach the olfactory bulb. Head trauma can shear these delicate filaments, causing permanent anosmia, classically after occipital impacts that shift the brain relative to the skull base. Uncal damage causes complex seizure phenomena rather than isolated anosmia, and trigeminal fibres mediate irritant sensations such as ammonia, not odour perception.

Reference: Gray's Anatomy for Students, 4th ed.

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Written and medically reviewed by the StethoPrep medical team.