What does CN XII deviation to one side indicate?

The deviation of the hypoglossal nerve (CN XII) to one side typically indicates atrophy and nerve impairment affecting the muscles of the tongue on that side. CN XII is responsible for the motor control of the intrinsic and extrinsic muscles of the tongue. When there is a lesion or impairment affecting the nerve on one side, the corresponding muscle becomes weak or atrophied, resulting in the tongue deviating towards the side of the affected nerve during protrusion.

This observation can be critical in diagnosing conditions such as a lower motor neuron lesion, which may result from trauma, tumor, or other neurological conditions. The presence of atrophy in conjunction with the deviation can point precisely to the location and nature of the nerve impairment. Understanding the muscle mechanics and nerve innervation is essential for accurate clinical assessment in ENT practice.