The paramedian arteries “represent a special differentiation of the highest of the group of paramedian arteries which can be found all along the neuraxis.” They arise from the P1 section of the posterior cerebral artery, to which the term “mesencephalic artery” may correctly be applied, as it is “the proximal stretch of the posterior cerebral artery from the bifurcation of the basilar to its junction with the posterior communicating” artery. The paramedian arteries can arise as a pair from each P1, but they may arise equally from a common trunk off 1 P1, thus supplying thalamus bilaterally (Artery of Percheron).
Clinically, unilateral thalamic infarction in the territory of the paramedian artery produces neuropsychological disturbances predominantly in the areas of arousal and memory. A left-right asymmetry is evident in language versus visual spatial deficits. Impairment of arousal with decreased and fluctuating level of consciousness is a conspicuous feature in the early stages, lasting for hours to days. Confusion, agitation, aggression, and apathy may be persistent features. Bilateral infarction in the paramedian artery territory may result in an acutely ill and severely impaired patient. Disorientation, confusion, hypersomnolence, deep coma, “coma vigil” or akinetic mutism (awake unresponsiveness), and severe memory impairment with perseveration and confabulation are prominent behavioral features, often accompanied by eye movement abnormalities.
- Schmahmann JD. Vascular syndromes of the thalamus. Stroke. 2003 Sep;34(9):2264-78. Epub 2003 Aug 21.