Clinical Examination of the Hypoglossal Nerve (CN XII)

Examination Technique

The American College of Radiology recommends asking the patient to protrude their tongue and observe for deviation toward the side of any lesion, which is the primary clinical sign of hypoglossal nerve palsy, in patients with suspected hypoglossal nerve dysfunction 1, 2
The American College of Radiology suggests looking for unilateral wasting or fatty infiltration, which may be visible as decreased bulk on the affected side, as a sign of chronic denervation in patients with hypoglossal nerve palsy 2

The American College of Radiology recommends listening for dysarthria, particularly difficulty with lingual consonants, which indicates impaired tongue motor function, in patients with suspected hypoglossal nerve dysfunction 1, 3
Dysarthria is a key clinical manifestation of hypoglossal nerve dysfunction, according to the American College of Radiology, and is characterized by difficulty with speech articulation 2, 4

The American College of Radiology states that the tongue protrudes in the midline without deviation to either side in healthy individuals 1
Normal articulation without dysarthria is expected in healthy individuals, according to the American College of Radiology 3

The hypoglossal nerve provides somatic motor innervation to all intrinsic tongue muscles and three extrinsic tongue muscles, with the exception of the palatoglossus muscle, as described by the American College of Radiology 1, 3
The nerve exits the skull through the hypoglossal canal and travels caudally within the carotid space before coursing anteriorly inferior to the hyoid bone, according to the American College of Radiology 3, 5

The American College of Radiology warns against confusing tongue deviation with facial asymmetry from facial nerve palsy, which affects facial muscles but not tongue protrusion 1

The American College of Radiology suggests that lower motor neuron (LMN) lesions of the hypoglossal nerve cause tongue deviation toward the side of the lesion with visible atrophy and fasciculations, while upper motor neuron (UMN) lesions cause deviation away from the lesion side without atrophy or fasciculations, and LMN lesions are most commonly caused by neoplasms involving the hypoglossal canal or extracranial segment 6
The American College of Radiology recommends that patients with LMN lesions may present with dysarthria with difficulty articulating lingual consonants, and nuclear lesions are typically accompanied by additional brainstem signs 6
The American College of Radiology notes that lesions at the jugular foramen or brainstem may affect multiple lower cranial nerves (CN IX-XII) simultaneously, creating complex clinical pictures, and assessment for associated signs such as other cranial nerve involvement (CN IX, X, XI) is necessary 6