HYPOGLOSSAL NERVE PALSY - A SEGMENTAL APPROACH

Hypoglossal nerve (cranial nerve XII) palsy is uncommon. Damage to thi s nerve produces characteristic clinical manifestations, of which unil ateral atrophy of the tongue musculature is the most important. When t hese features are recognized, the radiologist, armed with knowledge of the normal anatomy of the area, can focus on each segment of the nerv e in search of a cause. The hypoglossal nerve is divided into five seg ments: the medullary, cisternal, skull base. nasopharyngeal/oropharyng eal carotid space, and sublingual segments. Because each segment is us ually affected by different disorders, localizing a lesion to a partic ular segment allows the radiologist to narrow the differential diagnos is. In this way, the most efficient imaging strategy for evaluation of the symptoms can be developed. Both computed tomography and magnetic resonance imaging are useful in assessing dysfunction of the hypogloss al nerve; the choice depends on the status of the patient and the pref erence of the radiologist.