Variation of Blood Supply of Hippocampus

Meteeb (2020): Blood variation in hippocampus Oct 2020 Vol. 23 Issue 14 Variation of blood supply of hippocampus

Riadh Lafta Meteeb 1*

1 Head of unit of Anatomy, College of Medicine, University of Kufa, Najaf, Iraq

*Corresponding author: [email protected] (Meteeb)

Abstract 15 adult cadavers (30 hemispheres of the brain) were studied using formalin-fixed brain tissues which were examined by the magnifying lens. After identifying the hippocampus, the arteries in the area of the hippocampus were dissected with caution. It was found that the anterior choroidal artery and the lateral choroidal arteries (L.P.ch.As) were present in 100% of the examined hemispheres, A. ch. A, anastomosing with the anterior branches of L.P.ch.A in 31% of hemispheres. The hippocampal artery, a branch of the posterior artery was present in 82.8%. The anterior and middle temporal arteries were present in 80% of specimens. These results were discussed and compared with previous studies.

Key words: Anatomical study, hippocampus artery, blood supply

How to cite this article: Meteeb RL (2020): Variation of blood supply of hippocampus, Ann Trop Med & Public Health; 23(S14): SP231404. DOI: http://doi.org/10.36295/ASRO.2020.231404

Introduction: A part of the brain which is located in the cortex is called the limbic system which is important in the treatment of epilepsy and seizure (1). This system consists of the uncus, amygdaloid body, cornu ammonis, dentate gyrus, subiculum, fascicular gyrus, and the parahippocampal gyrus. The blood supply of this system is key to the surgical treatment of pathologies in this region. The term “hippocampus” is often restricted to the macroscopic swelling in the floor of the inferior horn of the lateral ventricle; it consists of a complexly folded layer of the dentate gyrus and the cornu ammonis, the latter being continuous through the subicular region with the parahippocampal cortex (2). In this study, the contributions of the vessels supplying the hippocampus were identified and compared with variations found in other studies.

Materials and Methods: Formalin-fixed brains from 15 adult cadavers (30 hemispheres) were examined under X6 to X16 magnification using a magnifying lens. The hippocampus was identified as it lies in the inferno-medial margin of the temporal lobe. It is on the floor of the inferior horn of the lateral ventricle. The veins in the area were removed, and the contributions of the anterior choroidal (A.ch.A.) and the posterior cerebral arteries (P.C.A.) that supply the hippocampus were studied.

Results Both the anterior choroidal (A.ch.A.) and the branches of the posterior cerebral arteries (P.C.A.) contribute to the supply of the hippocampus. The anterior choroidal artery (A.ch.A.) was found in 100% of the examined specimens, originating from the supraglenoid segment of the internal carotid artery (I.C.A.). It ran medially beneath the optic tract and lateral to the crus cerebri, and into the choroid fissure. It gave origin to 1-2 hippocampal branches that give blood vessels to uncus, the hippocampal gyrus, cornu ammonia and the dentate gyrus (Fig. 1, 2, 3).

Posterior cerebral artery (PCA) There are many methods for classifying the posterior cerebral artery (3, 4). According to Zeal and Rhoton (5), the posterior cerebral artery is divided into three segments; 1, 2 and 3. Segment 2 is a segment located between the posterior communicating artery and the posterior aspect of the midbrain. On the other hand, this segment can also be subdivided into anterior and posterior parts, which are called P-2A and P-2P, respectively. The posterior cerebral artery includes the circumflex artery, the thalamogeniculate artery, the medial posterior choroidal artery (MPChA), the lateral posterior choroidal artery (LPChA), and cortical Annals of Tropical Medicine & Public Health http://doi.org/10.36295/ASRO.2020.231404

branches (Fig 5, 6). In this study, we study the vessels that arise from P-2 and P-3 segments, mainly those giving branches to the hippocampus. The branches that supply the cortex of the posterior cerebral artery are divided into four segments: a) Inferior temporal artery. b) parieto-occipital artery. c) Calcarine artery. d) Splenial artery. The inferior temporal arteries are of five types: hippocampal artery, anterior temporal artery, middle temporal artery, posterior temporal artery and common temporal arteries (5) (Fig. 4, 5).

We found that the PCA supplied the hippocampus by cortical branches that include the hippocampal artery, the anterior and middle temporal arteries, and the lateral posterior choroidal arteries (LPChAs). The hippocampal artery, which gives branches to the uncus, the cornu ammonis, and the dentate gyrus, was seen in 82.8% of hemispheres. The origin of hippocampal artery was as follows: from P-1 segment (2.8%), from P-2A (48.6), from P-2P (20%), from P-3 -from calcarine artery- (8.6% ) and the common temporal artery (2.8% ) (Table 1 and Fig. 4, 5). 80% of hemispheres showed anterior temporal artery. In 40%, 37.2%, and 2.8% of specimens, it arises from P-2A, P-2P and P-3, respectively (Fig. 4, 5, 6). Two areas were found to be supplied by an anterior temporal artery which is the hippocampus and the inferior surface of the temporal lobe.

The middle temporal artery was present in 80% of the hemispheres. The pattern of its origin was as follows; in 25.7% from IP-2A, in 45.7% from P-2P, and in 8.6% from P-3 (Fig. 4, 5). It was shown that the inferior temporal, as well as the occipital surface (including the occipital pole and lingual gyrus), were supplied by the posterior temporal artery (Fig. 5). In terms of its origin, it was from segment P-2A, P-2P, P- 3, and the calcarine artery in 2.8%, 17%, 54%, and 2.8% of specimens, respectively. Only 16% of the specimens showed the common temporal artery with P-2P and P-3 segment as origins in 14.3%, and 5.7%, respectively. The area that was shown to be supplied by this artery was the inferior surface of the temporo- occipital lobe. The contribution to the arterial supply of the hippocampus was not shown.

Lateral posterior choroidal arteries (LPChAs) In each hemisphere, there were 2-4 lateral posterior choroidal arteries (LPChAs), but usually 3 in number (Fig. 2, 4). In 43% of cases, we found 2 lateral posterior choroidal arteries. In 40% of cases, there were 3 lateral posterior choroidal arteries and 4 (LPChAs) in 17% of cases. If more than one lateral posterior choroidal arteries were present, so these branches will be divided into 2 branches, that is, anterior and posterior (Fig. 3, 4). 2P segment was the origin of the lateral posterior choroidal arteries in 44.8%, while it showed 2A segment as an origin in 19.5%. It is 9.2% of specimens, the origin was from segment 3. About 26.5% was found to receive supply from cortical branches of PCA.

This study shows that the anterior branches of lateral posterior choroidal arteries anastomosed in 31% of specimens with the anterior choroidal artery (Fig. 2). There was no relation between the size of the anterior choroidal and the lateral posterior choroidal arteries. During this course, the LPChA gives branches to several parts. Firstly, it supplies the crus and commissure. In addition, it gives branches to the body and parts of the anterior columns of the fornix. Furthermore, it supplies the dorsomedial thalamic nucleus, pulvinar, and the lateral geniculate body (Margolis et al, 2002). The distributions of the arteries that supply the hippocampus are summarized in table (1).

Figure 1: show branches from anterior choroidal artery which gives 1-2 hippocampal branches to hippocampal gyrus.

Figure 2: shows anterior choroidal artery which gives branch to cornu ammonis.

Figure 3: shows anterior choroidal artery gives branches to dentate gyrus. A: Right, B: Left.

Figure 4: show branches from posterior cerebral artery which divided into: A: Anterior part, B: Posterior part.

Figure 5: show branches from posterior cerebral artery segment P1, P2

Figure 6: Inferior cerebral dissection to expose left internal capsul. Temporal horn of lateral ventricle is exposed. 1-optic nerve, 2-optic chisma, 3-internal capsule, 4-anteror border of internal capsule, 5-crus cerebri, 6-anterior commissure, 7-third ventricle (lamina terminalis open), 8-pons, 9-head of hippocampus, 10-choroid plexus of temporal horn of lateral ventricle, 11-optic radiation.

Table (1): Arterial supply of the hippocampus in 30 Hemispheres.

% of branches Site of Origin (% of No. of branches present Arteries present hemispheres) per hemisphere Supraclenoid segment of AChA 100.0 1-2 ICA Branches Cortical P-1 P-2A P-2P P-3 from PCA branches *HiA 82.2 2.8 48.6 20.0 8.6 2.8 1 *ATA 80.0 0.0 40.0 37.2 2.8 1 *MTA 80.0 0.0 25.7 45.7 8.6 1 *PTA 77.1 0.0 2.8 17.2 54.0 2.8 1 *CTA 16.0 0.0 0.0 14.3 5.7 0.0 1 LPChA 100.0 19.5 44.8 9.2 26.5 2-4

AChA: anterior choroidal artery, HiA: hippocampal artery, ATA: anterior temporal artery, MTA: middle temporal artery, PTA: posterior temporal artery, CTA: common temporal artery. Neither PTA nor CTA contributed to the supply of the hippocampus. LPChA: lateral posterior choroidal artery, PCA: posterior cerebral artery. * denotes cortical branches of a posterior cerebral artery.

Discussion: It is apparent from this study that 1-2 hippocampal branches of the AChA (anterior choroidal artery) supplies mainly the proximal (rostral) and middle portions of the hippocampus, whereas branches from P-A and P-2P segments of PCA supply mainly the middle and distal (caudal) regions of the hippocampus. The results confirm previous observations (6, 7), but differed somewhat in the variations made by the branches of PCA. There were variations in the contributions of these two sets of branches to the arterial vascularization of the hippocampus. In our study, the distribution of the AChA varied with that of the hippocampal cortical branches of PCA; in the absence of the latter, the AChA give blood supply to most of the hippocampus (Fig. 6). This is in accordance with the previous study by Erdem et al, (8). The hippocampal branches of PCA were seen in 82.2% of specimens under investigation, while Zeal and Rhoton (5) reported that the hippocampal branches of PCA are present in 64% of specimens.

It is usual for the anterior branches of LPChAs to arise from P-2A or its cortical branches. However, this study showed that the anterior branches of LPChA were anastomosed with the AChA (Fig. 2) in 31% of specimens. According to Carpenter et al. anastomosis was found between AChA and LPChA in 93%. A numerous inter-territorial anastomosis between these vessels was found inside the temporomesial region that a selective pre-surgical Wada test is needed to evaluate its functions (9, 10). It was proved that the size of the LPChA was related in a way proportional to the size of AChA (3, 11, 12).

According to Marinkovic et al, (13) there are two to seven hippocampal arteries, arranged in three sets; (a) the anterior hippocampal arteries originated from AChA, from ATA, and from the main trunk of PCA; (b) the middle hippocampal arteries originated from the common temporal artery and the main trunk of PCA; (c) the posterior hippocampal arteries arose from the main trunk of PCA and the splenial artery. In our study, the common temporal and the posterior temporal arteries did not contribute to the arterial supply of the hippocampus.

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