|Year : 2021 | Volume
| Issue : 4 | Page : 221-225
Study of Variations of Posterior Communicating Artery and Types of Posterior Circulation in Human Cadaveric Brains of South Indian Population
PR Prefulla1, E Mohanapriya1, Elamathi Bose2, S Keerthi1
1 Assistant Professor, Institute of Anatomy, Madras Medical College, Chennai, Tamil Nadu, India
2 Associate Professor, Department of Anatomy, Government Medical College, Thiruvallur, Tamil Nadu, India
|Date of Submission||11-Oct-2020|
|Date of Acceptance||30-Sep-2021|
|Date of Web Publication||21-Dec-2021|
Dr. S Keerthi
Institute of Anatomy, Madras Medical College, Chennai - 600 003, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Introduction: Posterior communicating artery (PComA) is the communicating channel between the internal carotid and vertebrobasilar arterial systems. The hemodynamics of the circle of Willis is influenced by variations in the PComA. Such variations may predispose to ischemic stroke due to inadequate collateral supply. Knowledge regarding the variations of the PComA and posterior circulation is of much clinical importance. Material and Methods: Eighty-eight posterior communicating arteries in 44 human cadaveric brains were studied. The morphological variations and morphometry of PComA and the various types of posterior circulation were noted and analyzed. Results: Morphological variations in PComA consisted of hypoplasia (17.04%) and aplasia (7.95%). The mean length of PComA was 12.72 ± 3.10 mm on the right side and 13.11 ± 3.37 mm on the left side. The four types of posterior circulation were adult type (78.41%), persistent fetal type-partial (12.5%), transitional type (5.68%), and persistent fetal type full (3.41%). Discussion and Conclusion: This study provides a comprehensive description of variations of PComA and types of posterior circulation. Awareness of these anatomical variations will be useful to anatomists, neurophysicians, neurosurgeons, and radiologists.
Keywords: Aplasia, circle of Willis, hypoplasia, partial persistent fetal type and full persistent fetal type, transitional type
|How to cite this article:|
Prefulla P R, Mohanapriya E, Bose E, Keerthi S. Study of Variations of Posterior Communicating Artery and Types of Posterior Circulation in Human Cadaveric Brains of South Indian Population. J Anat Soc India 2021;70:221-5
|How to cite this URL:|
Prefulla P R, Mohanapriya E, Bose E, Keerthi S. Study of Variations of Posterior Communicating Artery and Types of Posterior Circulation in Human Cadaveric Brains of South Indian Population. J Anat Soc India [serial online] 2021 [cited 2022 May 24];70:221-5. Available from: https://www.jasi.org.in/text.asp?2021/70/4/221/333190
| Introduction|| |
Posterior communicating artery (PComA) is a branch of the intracranial part of internal carotid artery (ICA). It courses posteriorly and ends by anastomosing with posterior cerebral artery (PCA). It is the communicating channel between internal carotid and vertebrobasilar arterial systems and contributes to the formation of circle of Willis (CW). PComA gives off many small branches which pierce the posterior perforated substance and supply the medial surface of thalamus and walls of the third ventricle. Internal carotid system or anterior circulation supplies the frontal, parietal, and part of temporal lobes. Vertebrobasilar system or posterior circulation supplies the occipital and part of temporal lobes, along with the brainstem and cerebellum.
Padget described 8 stages in the morphogenesis of cranial arteries in human embryos. In Stage III (7–12 mm embryo), the developing ICA gives off ophthalmic artery, anterior cerebral artery, middle cerebral artery, and PCA [Figure 1]a. In Stage VII (40 mm embryo), communication is established between the PCA and the developing basilar artery, so that the precommunication segment of PCA becomes PComA [Figure 1]b. Henceforth, the definitive PCA appears to be a branch of basilar artery. Eventually, the vertebrobasilar system becomes the main source of blood supply to PCA and the caliber of PComA is reduced till its adult size is attained.,
|Figure 1: (a and b) Lateral view of human embryo showing the development of posterior communicating artery. ICA: Internal Carotid Artery, OA: Ophthalmic Artery, ACA: Anterior Cerebral Artery, MCA: Middle Cerebral Artery, PCA: Posterior Cerebral Artery, BA: Basilar artery. Yellow arrow in Figure b indicates posterior communicating artery|
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In literature, posterior circulation has been classified into four types based on the relative contribution from basilar and carotid systems [Figure 2]a, [Figure 2]b, [Figure 2]c, [Figure 2]d.,,
|Figure 2: (a-d) Schematic representation of circle of Willis showing the four types of posterior circulation. PComA: Posterior communicating artery, PCA: Posterior cerebral artery, P1: Precommunicating part of posterior cerebral artery|
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- Adult type – The main contribution to PCA is from the basilar system [Figure 2]a
- Transitional type – Equal contribution to PCA from the basilar system and carotid system [Figure 2]b
- Persistent fetal type-partial – The main contribution to PCA is from the carotid system [Figure 2]c
- Persistent fetal type-full – Entire contribution to PCA is from the carotid system [Figure 2]d.
The greatest variation in arterial caliber between individuals occurs in PComA. It is normally very small so that only limited blood flow occurs between the anterior and posterior circulations. However, in case of occlusion of either of the arterial systems, PComA serves as an important collateral channel and maintains cerebral perfusion. The hemodynamics of CW is influenced by variations in PComA. This predisposes the individual to ischemic stroke due to inadequate collateral supply., Hence, our study data will be of much use to anatomists, neurophysicians, neurosurgeons, and radiologists. There is added significance as very few studies have been done so far about the types of posterior circulation, out of which extremely few have looked explicitly for the presence of persistent fetal type-full.
- To study the incidence of PComA
- To study the length of PComA
- To study the external diameter of PComA and the incidence of hypoplastic PComA
- To classify posterior circulation based on the relative external diameter of PComA and the Precommunicating part of PCA
- To provide South Indian data for the above-mentioned parameters.
| Material and Methods|| |
Eighty-eight PComA of 44 cadaveric human brains were studied. Measurements were taken using digital vernier callipers. In the base of the brain, interpeduncular fossa was identified. Arachnoid mater was carefully dissected to expose the CW. Individual specimens were serially numbered and photographs were taken. Incidence, length, and external diameter of PComA were studied in detail. The type of posterior circulation was identified. The obtained data were statistically analyzed.
- Presence or absence of PComA
- Length of PComA: PComA was measured from its point of origin from ICA to its point of termination at PCA
- Hypoplastic PComA: PComA with external diameter ≤0.5 mm was considered as hypoplastic
- Type of posterior circulation: Posterior circulation was classified based on the relative external diameter of PComA and precommunicating part of PCA (P1).
- Adult type: External diameter of P1 > external diameter of PComA
- Transitional type: External diameter of P1 = external diameter of PComA
- Persistent fetal type-partial: External diameter of P1< external diameter of PComA
- Persistent fetal type-full: P1 is absent; PCA is a branch of ICA.
| Results|| |
Absence of PComA was observed only unilaterally (5 right and 2 left). PComA was absent in 7 specimens [7.95%, [Figure 3]]. The mean length of PComA was 12.72 ± 3.10 mm on the right side and 13.11 ± 3.37 mm on the left side. The length of PComA ranged from 7.98 mm to 18.14 mm on the right side and 6.71 mm to 17.75 mm on the left side. Hypoplastic PComA was found in 14 specimens [17.5%, [Figure 4]]. It was observed in 4 on the right side and 10 on the left side, of which it was bilateral in one specimen. All four types of posterior circulation were observed [Figure 5]a, [Figure 5]b, [Figure 5]c. The unilateral and bilateral incidence of each type is summarized in [Table 1]. Among the four types, the highest incidence noted was that of adult type (78.41%), followed by persistent fetal type-partial (12.5%). In specimens with absent PComA, PCA derived its blood supply from basilar artery. Hence, they were considered to be having adult type of posterior circulation.
|Figure 3: Absent PComA on right side. ICA: Internal Carotid Artery, PComA: Posterior communicating artery, PCA: Posterior cerebral artery|
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|Figure 4: Hypoplastic left PComA. ICA: Internal carotid artery, PComA: Posterior communicating artery, and PCA: Posterior cerebral artery|
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|Figure 5: (a) Circle of Willis showing adult type of posterior circulation on right side and Persistent fetal type-partial on left side. PComA: Posterior communicating artery, PCA: Posterior cerebral artery, P1: Precommunicating part of posterior cerebral artery, and ICA: Internal carotid artery. (b) Transitional type on right side. Note Persistent fetal type-partial on left side. PComA: Posterior communicating artery, PCA: Posterior cerebral artery, P1: Precommunicating part of posterior cerebral artery, ICA: Internal carotid artery. (c) Persistent fetal type- full on left side. Note adult type on right side. PComA: Posterior communicating artery, PCA: Posterior cerebral artery, P1: Precommunicating part of posterior cerebral artery, ICA: Internal carotid artery|
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| Discussion|| |
Absence of PComA found in the present study (7.95%) correlated with the findings of Kannabathula et al. (8%) and Ghanbari et al. (11%). Posterior communicating arteries are the main collaterals of the CW. Assessing their patency is important before any interventional procedure. In the present study, the length of PComA was found to be 12.72 ± 3.10 mm on the right side and 13.11 ± 3.37 mm on the left side. This correlates with the findings of Shubhangi, who reported that the mean length of PComA was 13.98 mm on the right side and 14.46 mm on the left side.
PComA with external diameter <0.5 mm, irrespective of length, was considered hypoplastic., Incidence of hypoplastic PComA was found to be 17.5%. This finding is in accordance with that of Kannabathula et al., 16%. The volume of blood flow in an artery is inversely proportional to its length and directly proportional to its width. Thus, the shorter and wider the artery, more efficient is the transmission of blood to its target tissues. Individuals with hypoplastic PComA are at higher risk of developing cerebral infarctions, due to insufficient collateral circulation. Hypoplastic PComA is difficult to be depicted in computed tomography angiography. This may lead to misinterpretation as absent PComA. Embryologically, hypoplasticity of arteries is explained by a deficiency in reticular fibers in the arterial tunica, which also predisposes them to aneurysms and eventual rupture. Sometimes, aneurysmal hypoplastic PComA may be erroneously interpreted as normal in angiography.
All four types of posterior circulation were reported by Veras et al. According to them, the most common was adult type (73.52%), followed by persistent fetal type-partial (14.70%). Transitional type and persistent fetal type-full were reported to be present in 2.94% each. The findings of the present study [Table 1] are in unison with their study. Many authors did not look explicitly for persistent fetal type-full.,,
In two of the three specimens with persistent fetal type-full, hypoplastic PCA was also seen as an accessory vessel [Figure 5]c. PCA was considered hypoplastic, as the external diameter was <1 mm., Hypoplastic PCA was 7–8 mm long and ended by ramifying into very small twigs. In one of the three specimens with persistent fetal type-full, the hypoplastic PCA was longer and supplied the PCA territory, along with variant PCA which arose from ICA.
Persistent fetal type of posterior circulation-partial/full is protective in ischemia of vertebrobasilar system, as the perfusion of PCA territory is well maintained through blood supply from ICA.
Individuals with fetal type of posterior circulation and concomitant atherosclerotic disease of ICA are prone to ischemic events in the PCA territory. This is because thrombotic material from atherosclerotic ICA may be dislodged into PCA through the wide PComA. Carotid endarterectomy might be beneficial in some patients with severe carotid stenosis and infarction in the territory of the PCA. In persistent fetal type-full, occlusion of ICA may be disastrous as a large area of brain is supplied by branches of ICA.
Leptomeningeal vessels are anastomoses up to 1 mm in diameter which can be formed between the branches of ACA and PCA and MCA and PCA. In an adult type of posterior circulation, when the CW provides insufficient collateral flow during an ischemic event, leptomeningeal vessels take over as secondary collaterals. This is extremely important in cases of aplastic PComA. In persistent fetal type, obstruction of ICA cannot be compensated by the development of leptomeningeal collaterals between PCA and MCA because they are derived from the same vessel. This makes collateral blood flow completely dependent on the anterior circulation of the contralateral side. Therefore, patients with fetal type of posterior circulation could be more prone to develop vascular insufficiency.
| Conclusion|| |
Knowledge about the variations of PComA and types of posterior circulation is of utmost importance in diagnosing cerebrovascular diseases by analyzing clinical scenarios and interpreting radiological images. This is also important in planning interventional procedures involving the CW. Hence, awareness of these anatomical variations is important and will be useful to anatomists, neurophysicians, neurosurgeons, and radiologists.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]