A 32-year-old woman presents with anosmia following a head injury sustained when the back of her head struck the floor. The mechanism of anosmia is BEST explained by:

• A Contusion of the olfactory cortex in the temporal lobe
• B Haematoma compressing the olfactory bulb within the anterior cranial fossa
• C Damage to the piriform cortex in the frontal lobe
• D Shear injury to the olfactory nerve filaments (fila olfactoria) as they pass through the cribriform plate of the ethmoid ✓

Explanation

The olfactory nerve is actually composed of about 20 fine unmyelinated filaments (fila olfactoria) that pass from the olfactory epithelium through minute foramina in the cribriform plate of the ethmoid to reach the olfactory bulb. Contre-coup acceleration of the brain relative to the skull tears these fragile filaments at the cribriform plate — the most common mechanism of post-traumatic anosmia even with occipital impacts. The cribriform plate is not the piriform cortex, and while olfactory cortex damage can impair recognition, the peripheral filament shear is the primary mechanism after blunt trauma.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.