Nuclear Lesions

The lateral medullary syndrome, known also as Wallenberg's syndrome, is the prototype lesion involving the nuclei of the ninth and tenth cranial nerves. The syndrome results from infarction of the medulla by vertebral artery thrombosis or dissection that may also produce occlusion of the opening to the posterior inferior cerebellar artery.y

Presenting symptoms often include a stabbing pain in the eye, face, or ear ipsilateral to the side of infarction, presumably as a result of involvement of the nucleus of the descending tract of cranial nerve V. Vertigo or a sense of dysequilibrium occurs commonly because of injury of the vestibular nuclei. Nausea and vomiting are often accompanying symptoms, and they may also arise from vestibular nuclei involvement. Intractable hiccups are rarely caused by lesions of the medulla but may be present in lateral medullary infarction. y Involvement of the nucleus ambiguus causes ipsilateral vocal cord paralysis and a hoarse voice, as well as ipsilateral weakness of the palate and pharynx. Palate elevation on phonation is asymmetrical, with the uvula drawn to the intact side, and the patient experiences dysphagia. Impaired sensation to pain and temperature occurs in a crossed fashion involving the ipsilateral face and contralateral limbs caused by, respectively, involvement of the descending tract of the cranial nerve V and the spinothalamic tract. Injury of spinocerebellar fibers and of the inferior cerebellar peduncle results in an unsteady gait and ataxia of the ipsilateral limbs. An ipsilateral Horner's syndrome occurs from involvement of the descending sympathetic fibers from the hypothalamus. Limb weakness, tendon reflex changes, and extensor plantar responses do not occur because the corticospinal fibers are ventrally located at this level of the medulla and are outside of the area of injury. Ipsilateral facial weakness may be present even though the infarction does not extend beyond the lateral medulla. The triad of Horner's syndrome, ipsilateral limb ataxia, and contralateral limb numbness reliably indicates lateral medullary infarction. y

Unless cerebellar infarction is also present, cranial CT often does not identify the infarction. y , y Imaging by MRI is clearly superior to CT to visualize lesions in the medulla. The prognosis for recovery from a lateral medullary CVA is generally good, although in some cases the infarction may be fatal because of secondary edema and herniation or obstructive hydrocephalus and increased pressure in the posterior fossa. The area of infarction may also be extended by propagation of clot into the basilar artery, or by vessel-to-vessel embolism from the vertebral artery to the basilar artery. y

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