Picture of Cranial Nerve 12 (Hypoglossal Nerve XII) Dysfunction and Assessment

Hypoglossal nerve is a motor cranial nerve for the muscles of the tunge.So,If the right CN 12 is dysfunctional, the tongue will deviate to the right. This is because the normally functioning left half will dominate as it no longer has opposition from the right. Similarly, the tongue would have limited or absent ability to resist against pressure applied from outside the left cheek.

This photo shows Cranial Nerve 12 Dysfunction: Stroke has resulted in loss of function of left CN 12. When patient sticks tongue out, it therefore deviates to the left.

Assessment is performed as follows:

•Ask the patient to stick their tongue straight out of their mouth.
•If there is any suggestion of deviation to one side/weakness, direct them to push the tip of their
tongue into either cheek while you provide counter pressure from the outside.