VARIATIONS IN THE POSTERIOR PART OF CEREBRAL …...4. Kamath SA study of dimensions of the basilar...

1 Journal of Advance Researches in Biological Sciences, 2013, Vol. 6 (1) 1-4

Variations in The Posterior Part of ............

1 2 3Gupta Vishnu , Agarwal Rakesh , Ramesh Babu C. S.1,2,3Department of Anatomy, Muzaffarnagar Medical College, Muzaffarnagar

Submitted on : -20-08-2013 Re-submitted on:-28-10-2013 Accepted on:-14-12-2013

VARIATIONS IN THE POSTERIOR PART OF CEREBRAL ARTERIAL CIRCLE

INTRODUCTION

Circulus arteriosus (Cerebral arterial circle) was first describe by

Thomas Willis in 1662 and connects the internal carotid system

with vertebrobasillar system. Posterior cerebral artery is a

terminal branch of the basilar artery formed at the upper

posterior border where it joins the posterior communicating

artery to help complete the circulus arteriosus cerebri in human 1being. Posterior part of circle is formed by the posterior cerebral

arteries (PCA), terminal branch of basilar artery (BA), connected

to internal carotid arteries (ICA) by the posterior communicating

arterie (PComA).

The PComA arises as a branch of supraclinoid part of ICA and

passes backwards and medially, medial to occulomotor nerve

and joins the PCA at the junction of P1 and P2 segments of PCA.

Surgically the PCA is divided into three segments- P1, P2 and P3

and supplies occipital lobe and inferomedial surface of temporal

lobe. P1 is the precommunicating segment and P2 is lateral to

junction of PComA extending into perimesencephalic cistern 2and P3 segment lies in the calcarine sulcus (Standring 2001).

Corresponding Author:

DR. VISHNU GUPTADepartment of Anatomy

Muzaffarnagar Medical College

Muzaffarnagar-251203, U. P. (India)

E-mail : [email protected]

Anatomy of the posterior circulation variable and complex . three

basic configuration of PComA has been described (Saeki et. al.

1977)- adult, fetal and transitional. In fetal configuration,

PComA continues as P2 segment of PCA and P1 segment is

hypoplastic so the internal carotid system is supplying the

occipital lobe.

Neurosurgery has seen the development of many vascular bypass

and shunting procedures for the treatment of stenosis, aneurysm,

occulusions of the arteries of the posterior cranial fossa. The

knowledge of the anatomical variations will significantly alter the

plan of surgical approach and determine the out come of 3,4revascularization procedure.

MATERIAL AND METHODS

Sixty formalin embalmed brain were studied during the period of

six year in dissection hall of Muzaffarnagar Medical College,

Muzaffarnagar. Human brain specimen were obtained from the

cadaver subjected to dissection. The brain was removed by

dissection method given in cunningham manual of practical 5anatomy.

The arachnoid and piamater over pons, medulla oblongata and

the inter peduncular cistern was removed carefully exposing the

basilar artery and its branches with the posterior part of the circle

of Willis. Posterior cerebral artery was traced from its origin to the

termination, posterior communicating artery was also observed.

Variation present were noted and photograph of best observed

variation was taken.

ABSTRACT

Introduction : The embryologic development of intracranial circulation is truly one of Nature's marvels. Recognition of anatomic variants

is increasingly important for various neurosurgical procedures. Posterior part of circle is formed by the posterior cerebral arteries (PCA),

terminal branch of basilar artery (BA), connected to internal carotid arteries (ICA) by the posterior communicating arteries (PComA).

Variations of posterior cerebral and posterior communicating arteries are not uncommon. Material & Method : We were studied 60 adult

fixed human brains during the period of six years in dissection hall of Muzaffarnagar Medical College, Muzaffarnagar for variations in the

posterior part of cerebral arterial circle. In eight cases (four right and four left), I.e. in 11.3 % cases, we observed hypoplasia of P1 segment of

posterior cerebral with a dominant posterior communicating artery continuing as posterior cerebral artery and supplying occipital lobe.

This configuration referred to as “fetal type of posterior communicating artery. This was also found in 28% cases (Avci & Baskaya, 2003).

In such cases the internal carotid artery provides major supply to the occipital lobe. This variant was found in 10 % cases unilaterally and 5

% cases bilaterally. (Caldemayer et al. 1988; Van Overbeeke et al 1991). These variations in the posterior part of cerebral arterial circle are

relevant to vertebro-basilar ischemia and infarcts in the territory of posterior cerebral artery.

Key Words : Posterior cerebral artery, fetal type of posterior communicating artery, vertebra-basilar ischemia.



OBSERVATION AND RESULT

The present study focuses on the presence of variation in the

posterior part of cerebral arterial circle. Out of Sixty circulus

arteriosus, anomalous posterior cerebral artery formation was

found in eight cases, 13.3% (as in Fig-2,3), in rest of the 52 cases,

86.67% (as in Fig-1), the formation of posterior cerebral artery

was normal. The diameter of pre communicating (P1) segment of

posterior cerebral artery was larger than that of posterior

communicating artery. In all eight variant cases, anomalous

structure were found unilaterally. It was observed that pre

communicating (P1) segment of the posterior cerebral artery was

comparatively very small in caliber than the posterior

communicating artery and post communicating (P2) and P3

segment of posterior cerebral artery on one side. It was appeared

that the posterior cerebral artery was continuation of posterior

communicating artery, branch of internal carotid artery. P1

segment of posterior cerebral artery were small and appears to be

of small caliber.

DISCUSSION

Posterior cerebral artery was embryologically a continuation of

posterior communicating artery hence persistence of the pattern

is referred to a fetal type or embryonic type. In such cases P1

segment of PCA is hypoplastic and the PComA continues as the

P2 segment. The ICA supplies the territories of the posterior

cerebral artery via a larger PComA which is referred to a “Fetal

type PComA”. (Von ovarbeeka et. al. (1991)6; Baskaya et. al.

(2003)7. In such cases occulusion of PCA dose not result in

infarction in the territories of PCA (Operkin & Anderson, 1997).

The incidence of fetal type PComA was widely studied by

workers. It varies from 4.4% to 40% as reported by several

authors as mention in the table. The incidence of fetal

configuration in the present study was 13.3% and It known to

vary between 11-24% cases (Kamath et. al. 1981, P.N.Jain et. al.

2007, N. Jaysree et. al. 1990)8,9,10.

The fetal configuration found in this study came similar or very

close the result reported by Van Overbeke et. al and Alpers et.

al11. but it was lower than the results reported by others as A.

Pedrosa et. al., AA Zeal et. al., N Saeki et. al., K K Bisaria et.

al12,13,14. The largest study of the circulus arteriosus cerebri by

Alpers J.et al. 837 brains have found that the anomaly was

present unilaterally in the 31%. Battarcharji SK. et. al. have found

incidence of particular anomaly to be in brain with infarction

27% against those central series (17%). A possible reason for the

wide range in the fetal configuration reported in various studies

may be the variation in nomenclature and have relied upon

rough estimation of diameter. It is important to note that, the

same circle of Willis may have different configuration of the

posterior bifurcation of the PCA as the same circle may have

adult configuration one side and fetal configuration on other

side. Therefore, the two primary visual area of same individual

may receive their blood form different source, one from the

basilar artery through the P1 segment (Adult configuration) and

other from ICA through the PComA (fetal configuration ) thus,

obstruction of the basilar artery, may damage the primary visual

area. One side without damaging the primary visual area of the

other side. The presence of anomalous origin of posterior

cerebral artery may assume considerable significance if one is to

ligate internal carotid artery or in case of obstruction of this

artery by embolus. In such cases the blood supply of area of

brain might be interrupted (Varea. M., Bansal P.G. 1970)15.

Functional failure of circle could arise from anatomical anomalies

of obstructive vascular disease in a component vessels of it

(Battacharji , S.K. et al. 1967)16

CONCLUSION

The detailed knowledge of the variations of PComA and various

configuration of circle of Willis are important for neurosurgical

interventions and interpretation of MRI angiographic studies

(Avci et. al. 2005). Because of its variability and complexity,

microsurgical approaches to posterior part of circle is consider

risky. Prior knowledge of variation of the posterior part of the

cerebral arterial circle is also relevant for proper interpretation of

cases of internal carotid or vertibrobasilar ischiemia and

infraction. Thorough knowledge of the variant pattern is of

utmost important to anatomists, neurologists, neurosurgeons

and neuroradiologists.

Table-1: Prevalence of fetal type PComA

Name of Author

De Silva et al

Tulleken & Luiten

Padmavathi et al

Van Overbeke

Alpers & Berry

Pedrosa et al

Kamath

Avci & Baskaya

Saeki & Rhoton

Bisaria

Zeal & Rhoton

Present Study

Fetal type PcomA (%)

4.4%

11%

13%

14%

15%

22%

25%

28%

30%

32%

40%

13.3%

Year

2009

1987

2011

1991

1963

1987

1981

2003

1977

1984

1978

2013



Figure-1 : Normal adult configuration of the posterior part of the circle with the PCA larger in size than the PComA. Note the P1 and

P2 segments of PCA, BA = Basilar artery, ICA = Internal carotid artery, MCA= Middle cerebral artery, PCA = Posterior cerebral artery,

PComA= Posterior Communicating artery, SCA= Superior cerebellar artery.

Figure-2 : Fetal configuration – right side on the right side fetal type posterior cerebral artery is observed. P1 segment of PCA is

hypoplastic and gives posterior choroidal branch.PComA is continuing as P2 segment. (BA = Basilar artery; ICA = Internal carotid

artery, MCA= Middle cerebral artery; PCA = Posterior cerebral artery; PComA= Posterior Communicating artery, SCA= Superior

cerebellar artery; ACA=Anterior cerebral artery;)



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Figure-3 : Fetal configuration – left side PComA is continuing as P2 segment of PCA. The hypoplastic P1 segment passes

anterolaterally to connect with PComA. Two posterior choroidal branches(PChA) are given off by P1 segment of PCA. (BA = Basilar

artery; ICA = Internal carotid artery, MCA= Middle cerebral artery; PCA = Posterior cerebral artery; PComA= Posterior

Communicating artery; SCA= Superior cerebellar artery)

VARIATIONS IN THE POSTERIOR PART OF CEREBRAL …...4. Kamath SA study of dimensions of the basilar...

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