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Journal of the Anatomical Society of India

Variations of the Anterior Cerebral Artery in human cadavers: A dissection study

Author(s): Paul S and Mishra S.

Vol. 53, No. 1 (2004-01 - 2004-06)

Maulana Azad Medical College, New Delhi.

Abastract:

50 specimens of brain were studied in the dissection hall of Maulana Azad Medical College, New Delhi over a period of five years. The brains were removed from the cranial cavity and the branching pattern and course of the anterior cerebral arteries were observed. Out of the 50 specimens dissected 9 of them showed an aberrant course and anastomosis between the anterior cerebral arteries of both the hemispheres. Most of the anastomoses were seen on the orbital surface of the frontal lobe. Arteries on both sides showed differences in their size also. The knowledge of this anatomical variation may be of consderable help to the neurosurgeons.

Key words: Circle of willis, anterior communication, anastomosis, orbital surface.

Introduction:

In 1962, Thomas Willis was the first scientist to describe the circuls arteriosus, the major blood supply to the brain. Since then many anatomical variations have been reported on different branches forming the circle of Willis by various authors pertaining to the formation, developemt and size of the principal arteries (Orlando et al, 1986; Pchadus-orts et al, 1975; Kamath, 1981 and Van overbreek et al, 1991)The circulus arteriosus has an important role in maintaining a stable and constant blood flow to the cerebral hemisphere (Puchabus-orts et al 1975). The majority of vessels contributing to the formation of the circulus arteriosus are the anterior cerebral, middle cerebral and posterior cerebral. Most of the anatomical variations have been reported on the posterior cerebral and posterior communication arteries. however there are very few case reports regarding the variations encountered in the anterior cerebral arteries and their communications (Wisoff & Flamm, 1997, Kayambe et al, 1984 & Koyoma, 2000) Hence the present study was undertaken, to study the origin, course and termination of the anterior cerebral arteries, to observe the anterior communicating artery and to observe other variations between the two sides.

Materials and Methods:

50 Brains were taken out from cadavers from the dissection hall of Maulana Azad Medical College. Circulus arteriosus was observed in the interpeduncular cistern. The arachnoid mater was carefully removed. The anterior cerebral artery was traced from its origin to its termination, anterior communicating artery was also observed. All variations encountered were noted. From each specimen detailed drawings and photographs were made.

Observations:

Out of 50 brains dissected 9 of them showed aberrant course of the anterior cerebral arteries, the branching pattern and the anterior communicating artery showed a number of anomalies. The 9 cases, which showed anomalies, are described as follows.

Case 1.

The anterior cerebral artery of left side crossed over to the right side and the main stem curved to the orbital surface to supply both sides by small anastomotic channels. The left branch was thinner than the right side.

Case 2.

A common stem was seen arising from the anterior part of circle of Wilis. It divided into two branches and again joined further to divide into two branches after a brief course of about 1.5 cm. The left branch had a curved course before going to the orbital surface of the same side. The right branch deviated towards the right side and coursed alog the longitudinal fissure to supply the orbital surface of the same side. Both branches also had a number of anastomotic channels.

Case 3.

The two anterior cerebral arteries were joined by the anterior communicating artery as seen in normal cases. Immediately after communication the right anterior cerebral artery separated from the left and took a curved course to join the left branch and then traversed forwards along the medial border of the orbital surface. They also showed communications in addition to the anterior communicating artery between the two sides (fig 1.)

Case 4.

The two anterior cerebral arteries arose from a single point. The left branch coursed for a short distance near the median plane and then curved to the orbital surface of the same side, whereas the right branch took a turn and curved to the opposite side.

Case 5.

The two anterior cerebral arteries seemed to be arising from a common stem showing a number of anastomotic branches between the two sides. The right branch is deviated from the midline and shows one communication immediately above the common stem (fig 2).

Case 6.

This specimen also showed a common stem with the anterior cerebral artery arising from it and took a tortuous course on to the left side before going to their respective sides.

Case 7.

Anterior cerebral arteries of both sides were of different calibers and they were joined by the anterior communicating artery. Right artery was distinctly larger than the left and crossed over to the left side. Before crossing it gave a major branch to the right side (fig 3).

Case 8.

The distances between anterior cerebral arteries were much more than normally seen.

Case 9.

The anterior cerebral and anterior communicating arteries were distinctly visible. The right artery deviated more to the left and both the branches showed communications in the midline. Thereafter they were running parallel to each other (fig 2).

Discussion:

Anastomoses between the two anterior cerebral arteries in addition to the anterior communicating artery have been observed. Narrowing of the anterior cerebral artery of one side was observed while the artery of the opposite side crossed over to compensate for the vascular insufficiency.

There are reports on agenesis and hypoplasia of the initial segment of the anterior cerebral artery and anterior communicating arteries resulting in a defective circulation. The circulus arteriosus offers a potential shunt in abnormal conditions such as occlusions and spasms. In normal circumstances it is not an equalizer and distributor of blood from differnt sources. In about 1/3 cases angiographic evidence of defective circulation have been observed, Puchades-Orts et al, (1975) Therefore, existence of an effective circulation can never be assumed on surgical procedures involving its feeders. There are few case reports indicating a variation of the anterior cerebral artery and the communicating artery observed during operation (Dunker and Harris, 1976; Wisoff & Flamm, 1997; Kayembe, 1984; Koyoma, 2000 & Hoksberegen et al, 2000). All surgical interventions of the anterior cerebral artery should be preceded by angiography. The present study confirms the high percentage of variation seen in case of the anterior cerebral artery.

References:

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  9. Wiseoff JR, Flamm ES. Aneurysm of the distal anterior cerebral artery and associated vascular anomalies. Neurosurgery 1987;20(5): 735-741.

Fig. 1.

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Anterior cerebral arteries joined by anterior communicating artery (arrow). Right branch is seen to separate out from the left branch and rejoins is showing additional communication (arrowhead)

Fig. 2.

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The Two anterior cerebral arteries arising from a common stem (arrow) and showing number of anastomotic branches between the two sides (*).

Fig. 3.

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Right artery (R) is larger than left (L) and crosses over to the opposite side. Before crossing, it gives a major branch (arrow).

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Fig. 1. Photomicrograph showing group of leydig cells between three seminiferous tubule. Masson's Trichrome X 600.

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Fig. 2. Photomicrograph of intertubular space showing lipid vacuolations in leydig cells, extracellular fat cells and increased peritubular firbroblastic activity. H & E X 600.

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