Posteromedial central arteries

The posteromedial central branches (Paramedian thalamoperforating arteries or thalamic-subthalamic arteries) are a group of small perforating arteries that arise predominantly from the P1 (precommunicating) segment of the posterior cerebral artery (PCA). They represent one of the two main groups of central perforating branches of the PCA, the posteromedial group being the more medially located set, as opposed to the posterolateral (thalamogeniculate) group.

Origin and Course

These branches originate from the posterosuperior aspect of the P1 segment of the PCA, which extends from the basilar artery bifurcation to the junction with the posterior communicating artery (average length ~6.8 mm, average diameter ~2.2 mm). Microsurgical studies have identified an average of approximately 3.4 thalamoperforating branches per P1 segment, and they are typically the most proximally originating branches from P1. They ascend through the posterior perforated substance in the interpeduncular fossa to reach their target structures. The anterior half of the posterior perforated substance is perforated by the paramedian thalamic arteries (mean diameter ~0.57 mm), while the posterior half is perforated by the superior paramedian mesencephalic arteries (mean diameter ~0.20 mm). In approximately 57% of specimens, both groups arise from a common trunk.

Territories Supplied

The posteromedial central branches supply the following structures:

• Medial thalamus: including the intralaminar nuclei, most of the dorsomedial nucleus, and the medial part of the ventrolateral nucleus

• Subthalamic region

• Posterior hypothalamus (shared with branches from the posterior communicating artery)

• Rostral paramedian midbrain (via the superior paramedian mesencephalic branches that often share a common pedicle)

Infarction in the territory of the thalamoperforating arteries characteristically involves the medial portion of the thalamus along the lateral wall of the third ventricle.

Anatomical Variants

A notable variant is the artery of Percheron, in which a single dominant thalamoperforating artery arising from one P1 segment supplies the bilateral medial thalami, with variable contribution to the rostral midbrain. Occlusion of this variant produces the characteristic pattern of bilateral paramedian thalamic infarcts with or without midbrain involvement. Additionally, when the thalamopolar (thalamotuberal) artery which normally arises from the posterior communicating artery is absent (in 3040% of the population), its territory is taken over by the posteromedial central (thalamoperforating) branches.

Clinical Significance

These perforating branches are particularly vulnerable during surgical interventions for basilar apex aneurysms due to their close proximity to the basilar artery tip. Occlusion leads to paramedian thalamic infarction, which can manifest with altered consciousness, vertical gaze palsy, memory impairment, and behavioral changes.