Paramedian thalamic and midbrain infarction: the 'mesencephalothalamic syndrome'.

Paramedian infarction in the region of the thalamus and upper midbrain may produce a wide range of neuro-ophthalmological, behavioural and motor abnormalities. The paramedian arteries arise from the first part of the posterior cerebral artery, also known as the basilar communicating artery. The particular arterial topography and its anatomical variation may result in unusual combinations of clinical signs, and infarction may be bilateral in some cases. Diagnosis is often aided by CT scanning and magnetic resonance imaging. Both atherosclerotic occlusion and embolism are thought to be responsible for these particular syndromes. We describe 3 cases that illustrate some of the various clinical features and underlying anatomical vascular arrangements which may be seen in this condition. Thalamic dementia was present in one case with evidence of bilateral thalamic infarction. A complex ophthalmoplegia and hemiparesis were seen in another case, and the third case had a combination of thalamic dementia and ophthalmoplegia.