Review Question - QID 217800

With baseline hypertension and hyperlipidemia, this patient presents with crossed neurological deficits as evidenced by left hemiparesis and right oculomotor palsy (classic "down and out" presentation due to unopposed lateral rectus and superior oblique action) with ptosis. Hence, this patient likely has Weber syndrome, which is due to a stroke affecting the right side of his midbrain.

Weber syndrome is a constellation of neurological symptoms that arise from ischemic damage to the midbrain. It is most commonly due to an occlusion of the peduncular perforating branches of the posterior cerebral artery. This primarily impacts the cerebral peduncles (where the corticospinal and corticobulbar tracts pass through) and oculomotor fibers. As a result, patients present with ipsilateral oculomotor deficits (eye pointing down and out, diplopia, and ptosis) and contralateral hemiparesis. A closely related midbrain syndrome is Benedikt syndrome. With a more paramedian region of insult, the medial lemniscus and red nucleus are affected and cause contralateral hemianesthesia with impaired proprioception and hemiataxia, respectively.

Kim and Kim review midbrain infarcts in a series of 40 patients. The majority of patients (68%) had posterior circulation vascular lesions that were responsible for the infarct. They identified 4 different subgroups of infarcts: anteromedial, anterolateral, combined, and lateral. Anteromedial infarcts presented with more ocular motor disturbances while anterolateral infarcts had ataxia/hemiparesis issues; combined patients often had both. Lateral infarcts had sensory abnormalities from the involvement of the trigeminal tract and medial lemniscus.

Incorrect Answers:
Answer 1: Internal capsule infarcts are lacunar infarcts, which occur with the occlusion of small penetrating arteries which supply deeper structures. There are 4 classical stroke syndromes involving the internal capsule: pure motor, ataxic hemiparesis, dysarthria-clumsy hand, and mixed sensorimotor. Pure motor causes contralateral hemiparesis of the face and body. Ataxic hemiparesis causes contralateral hemiparesis and ataxia. Dysarthria-clumsy hand causes dysarthria and contralateral hand weakness. Mixed sensorimotor, which also involves thalamic infarction, causes combined contralateral hemiparesis and sensory impairment.

Answer 2: Medulla infarcts can cause medial and lateral medullary syndromes. Medial medullary syndrome is caused by occlusion of paramedian branches of the anterior spinal artery or vertebral artery and presents with ipsilateral hypoglossal palsy, contralateral hemiparesis, and contralateral lemniscus sensory loss. Lateral medullary syndrome is caused by posterior inferior cerebellar or vertebral artery occlusion and presents with ipsilateral vestibular abnormalities, dysphagia, dysarthria, hoarseness, gait ataxia, and absent gag. There is additional loss of pain and temperature sensation in the ipsilateral face and contralateral body.

Answer 4: Occipital lobe infarcts can be seen with posterior cerebral artery occlusions. Classically, patients present with contralateral hemianopsia with macular sparing. The macula is spared due to collateral flow from the middle cerebral artery.

Answer 5: Pons infarcts can also cause distinct syndromes. The lateral pontine syndrome is due to anterior inferior cerebellar artery occlusion. Due to overlapping affected nuclei and tracts, it presents similarly to lateral medullary syndrome. However, lateral pontine syndrome manifests with facial nerve problems (paralysis, decreased taste from anterior 2/3 tongue, etc.) while lateral medullary syndrome affects the glossopharyngeal nerve (dysphagia, hoarseness, etc.). Locked-in syndrome can occur with occlusion to the pontine perforators of the basilar artery. Patients present with quadriplegia, bulbar manifestations, and preserved consciousness – they retain conscious control of only vertical eye movements.

Bullet Summary:
Weber syndrome, which manifests with ipsilateral ophthalmoplegia and contralateral hemiparesis, is caused by ischemia of the midbrain cerebral peduncle and oculomotor fibers.