Abstract
BACKGROUND Motor function of the tongue is controlled by the hypoglossal nucleus (the lower motor neuron) and its supranuclear innervation (the upper motor neuron). Tongue deviation due to muscle weakness on one side is common in brain stem stroke and is usually associated with dysarthria and dysphagia that decrease the patient's quality of life. This case report presents a typical but rarely discussed case of tongue deviation secondary to a brain stem stroke. In addition, it also offers a concise review of both the ipsilateral and the contralateral cortico-hypoglossal fibers that innervate the hypoglossal nucleus. Even though the direction of the tongue deviation offers essential clues to localizing the brain lesion, many providers lack experience and knowledge in this area. CASE REPORT We report the case of an 81-year-old right-handed male patient with right-sided hemiparesis, right lower facial droop, dysarthria, and tongue deviated to the right side without fasciculation or atrophy. The Babinski sign was positive on the right. Magnetic resonance imaging revealed an infarct in the left paramedian pontine. Since both the tongue deviation and the hemiparesis were right-sided, contralateral to the side of the lesion, we concluded that the lesion affected the cortico-hypoglossal fibers and the corticospinal fibers prior to their decussations. CONCLUSIONS The case report reviews the projections of the corticospinal fibers. Each hypoglossal nucleus receives input from both hemispheres, with the contralateral descending fibers passing through the medial part of the ventral pons and the ipsilateral descending fibers passing through the more lateral aspect of the pons. The decussation is generally located at the pontomedullary junction, with exceptions due to individual variance.