Occlusion of Basilar Artery and Branches

3. Decreased alertness. Hypersomnolence or frank coma can result from bilateral paramedian rostral brainstem dysfunction. After the acute phase, the patient may remain relatively inert and apathetic. Some patients sleep many hours a day unless stimulated or coaxed into activities.

4. Memory loss. Patients are unable to form new memories and may not be able to recall events just preceding their stroke. There often are other behavioral abnormalities, including agitation, hallucinations, and abnormalities that mimic lesions of the frontal lobe.

THALAMIC INFARCTS

The thalamus is supplied by arteries that arise at or near the basilar artery bifurcation and from the proximal posterior cerebral arteries. The tuberothalamic (polar) artery arises on each side from the middle third of the posterior communicating artery and supplies the anteromedial and anterolateral thalamic nuclei. Unilateral anterolateral thalamic infarction in the distribution of the polar artery on either side usually causes abulia, facial asymmetry, transient minor contralateral motor abnormalities and, at times, aphasia (left lesions) or visual neglect (right lesions). Abulia, with slowness, decreased amount of activity and speech, and long delays in responding to queries or conversation, is the predominant abnormality. Memory may also be affected.

The thalamic-subthalamic arteries (also called thalamoperforating) originate from the proximal posterior cerebral arteries and supply the most posteromedial portion of the thalamus near the posterior commissure. The right- and left-sided arteries usually arise separately but can originate from a single unilateral artery or a common pedicle. Unilateral lesions are usually characterized by paresis of vertical gaze (upward or both upward and downward) and by amnesia. Motor and sensory signs and symptoms are absent. Memory loss may be severe, with profound difficulty in forming new memories and encoding recent events, particularly with bilateral lesions. The amnesia often improves within 6 months in patients with unilateral infarcts. Bilateral butterfly-shaped paramedian posterior thalamic infarction can result from a branch occlusion of a single supplying artery or pedicle and cause hypersomnolence and bilateral third-nerve palsies.

The thalamogeniculate group of arteries arises from the posterior cerebral arteries to supply the ventrolateral thalamus, an area that includes the somatosensory nuclei (ventral posterior lateral and ventral posterior medial) and the ventral lateral and ventral anterior nuclei. The findings in patients with lateral thalamic infarcts are contralateral hemisensory symptoms accompanied by contralateral limb ataxia. At times, hemichoreic movements of the contralateral arm develop, and the hand may assume a fisted posture. Some patients have a transient hemiparesis at onset that improves quickly.

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