Intramedullary Course

DISORDERS OF THE HYPOGLOSSAL NUCLEUS AND NERVE

Supranuclear lesions affecting the corticobulbar fibers above their decussation result in weakness of the contralateral half of the tongue. Bilateral upper motor neuron lesions affecting the corticobulbar tracts cause significant tongue dysfunction and spastic dysarthria. Dorsal medullary lesions causing bilateral lower motor neuron lesions of the tongue are extremely rare but are seen on occasion with tumors or syringobulbia. The medial medullary syndrome (Dejerine anterior bulbar syndrome) is caused by occlusion of the anterior spinal artery supplying the medial lemniscus, hypoglossal nerve, and ipsilateral pyramids. Intramedullary lesions may also result from cavernomas, multiple sclerosis, syringobulbia, and intramedullary tumors. These lesions may present with ipsilateral paresis, atrophy, and fasciculations of the tongue, often accompanied by contralateral hemiplegia and contralateral loss of position and vibratory sensation. Anterior horn cell disorders, such as amyotrophic lateral sclerosis, frequently affect the hypoglossal nucleus.

Peripheral nerve lesions of the hypoglossal nerve result in tongue deviation to the side of the lesion. Atrophy, fasciculations, and increased furrowing may be observed on the side of the lesion. It is best to allow the tongue to rest on the floor of the mouth when assessing for fasciculations. Because of the close proximity to cranial nerves IX, X, and XI in the hypoglossal canal, basilar skull lesions in this area may damage all four of these cranial nerves, resulting in weakness of the sternocleidomastoid, trapezius, tongue, pharyngeal and laryngeal muscles, accompanied by loss of taste on the posterior third of the tongue and hemianesthesia of the palate, pharynx, and larynx (Collard-Sicard syndrome). Occipital pain and ipsilateral hypoglossal nerve injury may occur with occipital condyle syndrome, which is usually the result of tumors or chronic inflammatory lesions. Isolated hypoglossal neuropathy may also occur as the result of carotid aneurysm, vascular entrapment, dissection, local infection, rheumatologic disease, neck radiation, or tumors.

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