Anatomical Relationship Between the Thalamus and Circle of Willis
The thalamus is located superior (above) to the circle of Willis, positioned in the diencephalon at the base of the brain, where it receives blood supply from perforating arteries that branch directly from the circle of Willis structures.
Spatial Orientation
The thalamus sits as a deep brain structure in the diencephalon, directly above the circle of Willis arterial ring 1. The circle of Willis forms a vascular ring at the base of the brain in the subarachnoid space, with the thalamus positioned superiorly in relation to this arterial circle 2.
Vascular Supply Relationship
The thalamus receives its blood supply from perforating arteries that arise directly from components of the circle of Willis:
- Paramedian arteries branch from the P1 segment of the posterior cerebral artery (part of the circle of Willis) to supply the medial thalamus 3
- Tuberothalamic arteries arise from the posterior communicating artery (a key component of the circle of Willis) 3
- Inferolateral arteries branch from the P2 segment of the posterior cerebral artery to supply the lateral thalamus 3
- Posterior choroidal arteries also contribute to thalamic blood supply 3
The posterior cerebral arteries and posterior communicating arteries, which are integral components of the circle of Willis, give rise to these thalamic perforating vessels 1.
Clinical Significance
In pathological conditions affecting the circle of Willis, the thalamus is particularly vulnerable:
- Prominent collateral flow voids in the basal ganglia and thalamus on MRI are virtually diagnostic of moyamoya syndrome, where stenosis of circle of Willis vessels occurs 1
- Hemorrhage from moyamoya vessels commonly occurs in the thalamus, along with basal ganglia and medial temporal lobes 1
- Variations in circle of Willis configuration, particularly hypoplasia or absence of P1 segments or posterior communicating arteries, directly correlate with risk of ipsilateral thalamic infarction 3
- Overgrown perforating arteries serving as collateral circulation in circle of Willis occlusion can rupture within the thalamus, causing intracerebral hemorrhage 4
The thalamus essentially sits immediately above and is directly perfused by small penetrating vessels originating from the circle of Willis arterial ring 2, 3.