Cranial Nerve I: Olfactory

Fig. 12.1 Coronal CISS image highlights the presence of both olfactory bulbs lying just above the ethmoidal roof (arrow). Note the presence of normal olfactory sulci (arrowhead)

Fig. 12.2 Sagittal CISS image showing the olfactory tract (arrow) lying just above the ethmoid roof and below the gyrus rectus

12.2 Function

The olfactory nerve is one of the five special senses, consisting of only SA fibers. The olfactory nerve carries information involved in:

Recognition of odors
Emotional response to odors (including memories of pleasant and unpleasant sensations)
Autonomic response to odors (increased peristalsis and gastric secretion)

12.3 Pathology

Individual symptoms: Damage to the olfactory nerve results in the following symptoms:

Loss of smell at various levels from iposomia to anosmia. If ipsilateral, lesion is anterior to the piriform cortex.
Cacosmia: perception of unpleasant smells.
Parosmia (also troposmia): perversion of smell.
Olfactory hallucinations (aka uncinate fits) (Fig. 12.4).

12.3.1 Syndromes

Kallmann syndrome: A rare genetic disease, of which one component is the absence of olfactory bulb and tract in the olfactory groove [3]. There is variable presence of olfactory sulcus (Fig. 12.3).

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