The main purpose of the examination of facial sensation is to assess for lesions involving the fifth (trigeminal) cranial nerve. Another purpose is to assess for lesions of the sensory pathways in the cerebral hemispheres and brainstem that may also cause facial sensory loss.

Facial sensation should be tested in any patient who has a symptom of facial numbness or facial pain or in any patient suspected of having a disorder affecting cranial nerves. In patients who have no facial sensory symptoms or when there is no other particular clinical concern for a fifth nerve lesion or a disorder affecting cranial nerves, it is not imperative to test facial sensation routinely.

Sensation to the face is supplied by the three main branches of the trigeminal nerve: the ophthalmic division (V1, pronounced “vee one”), the maxillary division (V2), and the mandibular division (V3). Figure 15-1 illustrates the cutaneous sensory distributions of the three divisions of the trigeminal nerve.

The trigeminal nerve enters the brainstem at the level of the pons and then synapses with its sensory nucleus; from there, sensory information crosses to the other side to travel to the contralateral thalamus and parietal cortex.