Neuroanatomical study
Variations in the origin of the thalamoperforating arteries

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Abstract

The anatomy of the thalamoperforating arteries located in the interpeduncular fossa must be well understood by surgeons to enable safe surgical treatment of basilar and posterior cerebral artery aneurysms. Therefore, we studied 30 posterior cerebral arteries obtained from 15 fresh adult cadaver brains. By filling the vertebral and internal carotid arteries of the brains with coloured latex, we found thalamoperforating arteries in 97% of the brains studied. The average number of arteries was two (range 0–5). Thalamoperforating arteries were classified into four different types according to their origin at the P1 segment: type I (bilateral multiple), 20%; type II (unilateral multiple, unilateral single), 33%; type III (bilateral single), 40%; type IV (one side multiple, the other side with no branches), 7%. In conclusion, it is important to bear in mind that these arteries can be the unilateral single type, and that they may be absent on the other side. Unilateral single arteries are very significant for surgical technique.

Introduction

The posterior cerebral artery arises from the basilar artery in the interpeduncular fossa, and courses through the posterior brain after encircling the midbrain. The artery has a close relationship with many important neural structures during its course. Variations in the thalamoperforating arteries arising from the P1 segment of the posterior cerebral artery must be well understood by surgeons to enable safe surgical treatment of basilar artery aneurysms in the interpeduncular fossa.[1], [2], [3], [4], [5], [6], [7] The aim of the present study was to investigate the variations in these arteries in order to ensure safe surgical procedures in this region.

The basilar artery bifurcates and forms the posterior cerebral arteries in the interpeduncular cistern distal to the superior cerebellar artery. Posterior cerebral arteries pass from the superior surface of the oculomotor nerve, and after coursing through the anterior-medial part of the cerebral peduncle they unite with the posterior communicating arteries. The posterior cerebral arteries form the posterior part of the circle of Willis,[3], [8], [9], [10], [11] then they twist through the occipital pole and supply this region.

The posterior cerebral artery was divided into five segments (P1, P2, P3, P4, and P5) by Krayenbühl and Yaşargil.8 Although this segmentation has been modified by some authors, they have basically used the same segmentation system.[5], [9], [11], [12], [13], [14], [15]

The P1 segment is between the origin of the posterior cerebral artery and posterior communicating artery. This segment is variously called the peduncular, precommunicating, mesencephalic, circular or basilar segment.[2], [5], [9], [10], [11], [14], [16] Thalamoperforating arteries arise from this segment. The P2 segment (postcommunicating, ambient or perimesencephalic segment) is the part of the posterior cerebral artery located in the interpeduncular cistern. The P3 segment or quadrigeminal segment is the part of the posterior cerebral artery located in the quadrigeminal cistern.[9], [15] Most researchers call the parieto-occipital and calcarine arteries the P4 segment and the terminal part of this artery the P5 segment.[5], [11], [12], [13], [14] The thalamoperforating arteries (posterior and interpeduncular thalamoperforating arteries) usually arise from the P1 segment and rarely from the posterior communicating artery.[2], [17] These branches are called posterior thalamoperforating arteries when they arise from the P1 segment, and anterior thalamoperforating arteries (premamillary artery) when they arise from the posterior communicating artery.

The posterior thalamoperforating arteries enter the brain after passing from the posterior perforated substance, interpeduncular fossa and from the medial side of the cerebral peduncle. These arteries supply the posterior part of the thalamus, the hypothalamus, subthalamus, substantia nigra, red nucleus, oculomotor nucleus, trochlear nucleus, reticular formation of the midbrain, pretectum, rhomboid fossa and posterior part of the internal capsule.[10], [11], [12], [14], [17], [18], [19]

The aim of the present study was to investigate variations in the thalamoperforating arteries that arise from the P1 segment of the posterior cerebral artery.

Section snippets

Materials and methods

We used 30 posterior cerebral arteries obtained from 15 fresh adult cadaver brains. The vertebral and internal carotid arteries of the brains were filled with coloured latex. The specimens were fixed with 10% formalin, and then the posterior cerebral arteries were dissected under a Zeiss OPMI 1 dissecting microscope (×40) (Carl Zeiss Inc., Oberkochen, Germany). During the measurements a digital compass was used, and photographs were taken by using a Leica M3 camera (Leica Microsystems AG,

Results

Thalamoperforating arteries were seen in 97% of cases. The average number of these arteries was two (range 0–5). They arose from the superior or posterior surfaces of the P1 segment and entered the brain from the interpeduncular fossa, posterior perforated substance and cerebral peduncle.

Thalamoperforating arteries were classified into four different types according to their origin at the P1 segment:21

  • Type I (bilateral multiple): multiple thalamoperforating arteries in more than two branches on

Discussion

Awareness of variations in the basilar and posterior cerebral arteries is important for the treatment of aneurysms of these arteries because their number arising from the P1 segment is variable. They can arise as a single thick branch or one, two or multiple small branches. Thalamoperforating arteries were first defined by Duret in 1874 as “posterior internal optic arteries”.12 Zeal, Rhoton and Saeki reported that these arteries are a group of branches that arise from the P1 segment of this

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