With right-sided lesions, there may be a left spatial neglect and constructional apraxia; slight disorders of speech and language may accompany left-sided lesions. Hupperts and colleagues have discussed the controversy regarding the effects of occlusion of the artery and in particular the variability of its supply to the posterior paraventricular area of the corona radiata and adjacent regions. They concluded, also from a survey of CT images, that there was no uniform syndrome attributable to occlusion of the vessel and that in most cases its territory of supply was overlapped by small surrounding vessels. It may be remembered that for a time, in order to abolish the tremor and rigidity of unilateral Parkinson disease, the anterior choroidal artery was being surgically ligated without these other effects having been produced.
Despite the small caliber of the vessel and its blood supply of deep structures, the most common cause of occlusion of this vessel is embolic (Leys and colleagues).
In approximately 70 percent of individuals, both posterior cerebral arteries are formed by the bifurcation of the basilar artery and thin posterior communicating arteries join this system to the internal carotid arteries. In 20 to 25 percent, one posterior cerebral artery arises from the basilar in the usual way, but the other arises from the internal carotid, a persistent fetal pattern of circulation (“fetal PCA”); fewer than 5 percent have the unusual configuration in which both arise from the corresponding carotid arteries. Most strokes in this territory are embolic in origin, either cardioembolic or from a thrombus in a more proximal vessel, but some individuals are predisposed to atherosclerosis in the proximal posterior cerebral artery.
The configuration and branches of the proximal segment of the posterior cerebral artery (P1 segment) are illustrated in Figs. 33-8, and 33-10. The interpeduncular branches, which arise just above the basilar bifurcation, supply the red nuclei, the substantia nigra bilaterally, medial parts of the cerebral peduncles, oculomotor and trochlear nuclei and nerves, reticular substance of the upper brainstem, decussation of the superior cerebellar peduncles, medial longitudinal fasciculi, and medial lemnisci. The P1 portion of the posterior cerebral artery is the segment that arises from the terminus of the basilar artery proximal to the ostium of the posterior communicating artery. It gives rise to the interpeduncular branches, which are variable and complex. As pointed out by Percheron (whose name is often applied to the largest of these vessels), the arterial configuration of the paramedian mesencephalic arteries varies considerably: in some cases, two small vessels arise symmetrically, one from each side; in others, a single artery arises from one posterior cerebral stem (proximal P1), which then bifurcates. In the latter case, one posterior cerebral stem, through a small artery, supplies the medial thalamic territories on both sides, and an occlusion of this artery produces a bilateral butterfly shaped lesion in the medial parts of the diencephalon. These are elaborated and illustrated by Castaigne et al.