Introduction
The hypoglossal nerve is a motor nerve supplying the intrinsic muscles of the tongue.
In XII nerve palsy the tongue deviates towards the affected side.
Anatomy
The hypoglossal nerve originates in the medulla then passes through the hypoglossal canal in the occipital bone (base of skull). It runs between internal carotid artery and internal jugular vein, then through the submandibular region to enter the tongue.
Testing
Ask the patient to stick their tongue out. Look for deviation, wasting and fasciculation.
Investigations
Investigations are the same as for CN IX.
Medical
The causes are as for jugular foramen syndrome:
- Tumours (metastases, neurofibromata, cerebellopontine angle lesions)
- Meningitis
- Infection from middle ear spreading into posterior fossa
Trauma
Isolated hypoglossal nerve injury has been reported in association with a foramen magnum fracture.