Incidence of fenestration of anterior communicating artery in Indian population using computed tomography angiography

Urvi Sharma; Suman Verma; Subathra Adithan

doi:10.4103/NJCA.NJCA_234_22

ORIGINAL ARTICLE

Year : 2023 | Volume : 12 | Issue : 1 | Page : 27-30

Incidence of fenestration of anterior communicating artery in Indian population using computed tomography angiography

Urvi Sharma¹, Suman Verma², Subathra Adithan³
¹ Senior Resident, Department of Anatomy, AIIMS, Raipur, India
² Additional Professor, Department of Anatomy, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India
³ Additional Professor, Department of Radiodiagnosis, Jawaharlal Institute of Postgraduate Medical Education and Research, Puducherry, India

Date of Submission	29-Nov-2022
Date of Decision	05-Jan-2023
Date of Acceptance	07-Jan-2023
Date of Web Publication	21-Feb-2023

Correspondence Address:
Urvi Sharma
Department of Anatomy, All India Institute of Medical Sciences, Raipur
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/NJCA.NJCA_234_22

Abstract

Background: Cerebral vasculature fenestration is a rare congenital anomaly and is mostly found in association with aneurysms. Fenestration involving anterior communicating artery (ACoA) is rare. The study's objective was to determine ACoA fenestration incidence in Indian population using computed tomography angiography (CTA). Methodology: Datasets of CT cerebral angiography in 105 patients (67 males and 38 females), of average age- 47.96±16.58 years were systematically reviewed for fenestration in ACoA. The cases with aneurysms and infarcts were excluded from the study. Results: The fenestration involving ACoA was seen in 0.95% (1/105). The fenestration was triangular and located in the proximal part of the artery. No other vascular anomaly was observed in ACoA. Conclusion: The incidence of ACoA fenestration is low in Indian population. Knowledge about the variations of cerebral vasculature will be helpful for radiologists and neurovascular surgeons while dealing with cerebrovascular diseases.

Keywords: Angiography, anterior communicating artery, fenestration

How to cite this article:
Sharma U, Verma S, Adithan S. Incidence of fenestration of anterior communicating artery in Indian population using computed tomography angiography. Natl J Clin Anat 2023;12:27-30

How to cite this URL:
Sharma U, Verma S, Adithan S. Incidence of fenestration of anterior communicating artery in Indian population using computed tomography angiography. Natl J Clin Anat [serial online] 2023 [cited 2023 Mar 20];12:27-30. Available from: http://www.njca.info/text.asp?2023/12/1/27/370141

Introduction

A pair of anterior cerebral arteries (ACAs) are joined by a tiny conduit called the anterior communicating artery (ACoA). It functions as a crucial anastomotic route for complementary circulation across the cerebral arterial circle.^[1] The ACoA arises from a multichannel vascular network throughout embryologic development, coalescing to variable degrees by the time of birth.^[2]

Anatomically, fenestration of the intracranial artery is a variant that occurs very seldom.^[3] It is usually asymptomatic and is detected when a patient is investigated for aneurysmal subarachnoid hemorrhage.^[4] Fenestration occurs due to incomplete anastomosis of paired primitive vessels.^[5] In this variation, a part of a vessel splits up into two divisions made up of endothelial layer and muscle layer with or without adventitia which coalesce into a single cavity.^[6],[7] Based on location, fenestration is divided into three types: near, middle, and far,^[8] and according to size and shape, it is divided into two types: fissure and convex lens. Fissure-type fenestration resembles a small hole, while in convex lens, it resembles a convex lens or fusiform shape.^[9]

According to surgical and anatomical research, fenestrations are prevalent in cerebral arteries with the greatest occurrence in the ACoA complex.^[7] Fenestrations have been linked to aneurysms and other neurovascular diseases. According to some authors, fenestration may cause a change in flow dynamics that might lead to aneurysms. However, it is unclear exactly how they relate to one another.^[7] Fenestration of ACoA is rarely associated with aneurysms which occur proximal to the fenestration.^[1],[4]

About 40% of specimens in significant autopsy and surgical series have been documented to have multiple fenestrations in the ACoA.^{[10],[11],[12]} In spite of this prevalent finding in anatomical studies, it is extremely rare to see fenestrations of the ACoA in angiograms.^[1] The incidence of ACoA fenestration in cases without associated aneurysms is not known in Indian population using computed tomography angiography (CTA), hence this study was planned.

Materials and Methods

This descriptive hospital record-based study was done in the Departments of Radiology and Anatomy at JIPMER, Pondicherry. The research was authorized by the Institute Human Ethics Committee (Ref. Number JIP/IEC/2019/421 dated December 12, 2019.

The CT cerebral angiography and multiphasic contrast-enhanced records, from picture archiving and communication system of the Department of Radiology, available from July 2017 to July 2020 were used. The conditions such as occlusion, dissection, aneurysm, and vasculitis that have effect on the normal vascular architecture of the circle of Willis were excluded from the study. The scans in which branching of the circle of Willis was not completely visible were also excluded.

CT angiogram was done using a 128-slice multidetector CT system, Siemens SOMATOM 64 (SOMATOM Definition Edge, Siemens, Germany). Three-millimeter slices were acquired with a 128 × 0.6 matrix and reconstructed to 1 mm width of slice. The duration of rotation was 0.5 s and of pitch was 1.2, and it delivered an effective mAs of 300 at a voltage of 120 Kv. The average acquisition time was around 10 to 15 s. Nonionic contrast (400 mg iodine/ml) with dosage at the rate of 4–6 ml/s with saline flush of 40 ml was given. The angiographic CT data sets were loaded in Siemens Syngo via server workstation, and 3D angiographic images were obtained using maximum intensity projection (selected and displayed voxels with high attenuation value), multiplanar reformation, and volume-rendered technique. The images could be rotated in any direction, and the axial images were directly analyzed for fenestration.

Results

A total of 105 CT cerebral angiograms [Figure 1] from 67 (63.80%) males and 38 (36.19%) females were studied. The average age of subjects was 47.96 ± 16.58 years (range: 11 to 85 years). The ACoA fenestration [Figure 2] was seen in 0.95% (1/105). The variant angiogram belonged to a 58-year-old female with a history of repeated episodes of headache who was referred to the Radiology Department for cerebral CTA. CT revealed an aplastic left A1 segment with an origin of ACoA, and bilateral A2 segments were arising from the right ACA. Furthermore, fenestration of ACoA was seen. The fenestration was triangular and seen near the proximal A2 segment of ACA. It was formed due to partial/segmental duplication of artery. The anterior limb of the fenestration was longer than the posterior limb. No other vascular anomaly was observed in ACoA.

Figure 1: Normal CT cerebral angiogram showing branches of circulus arteriosus. Segment of anterior cerebral artery; A1-A1 and A2-A2 segments. CT: Computed tomography

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Figure 2: CT cerebral angiogram showing fenestration of ACoA (black arrow), left aplastic A1 segment (yellow arrow). ACoA: Anterior communicating artery, CT: Computed tomography

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Discussion

The present study evaluated the ACoA in the 105 CTA records from the tertiary care hospital, and the fenestration of the ACoA was seen in 0.95%. Its reported prevalence is 0.3%–28%.^[13] It is difficult to estimate the true prevalence of fenestration of intracranial arteries (FIAs), and it substantially depends on the method of examination. The incidence in adult cadavers was 21%.^[4] The difference in the incidence on window examination varies from 0.7% to 60% in magnetic resonance angiography (MRA), CTA, and digital subtraction angiography examination.^[8] Fenestration of ACoA is common among all intracranial arteries followed by basilar artery and middle cerebral artery.^[14] In autopsy studies, fenestration of ACoA is the most common, but only 5% of cases of fenestration were seen in angiography.^[1] Sanders et al. found 37 fenestrations in 10 of 5190 cerebral angiograms, but none of them was seen in ACoA.^[8] The incidence of fenestration does not significantly correlate with gender.^[3]

Imaging is not commonly used to demonstrate fenestrations.^[6],[8] The incidence of fenestration was found to be much lower in conventional angiographic studies as compared to cadaveric studies [Table 1].^[15],[16] This is due to superimposition which limits the visualization of some variations in conventional angiography. However, the introduction of multidetector-row CTA has substantially increased the detailing in images of cerebral vessels.^[14],[21] In surgical and autopsy cases, the incidence of fenestration is approximately 40%. A large number of fenestrations are not visible on three-dimensional rotational angiography (3DRA) with the present resolution. This is because bridging arteries are not appreciable on 3DRA as they are very thin (0.1–0.3 mm).^[22] Before the advent of 3D imaging, fenestration was thought to be extremely rare. This might be because of the fact that fenestrations could only be seen at particularly viewing angles, which were frequently absent from 2D angiograms.^[7] The prevalence is somewhat greater, up to 13% with current 3D reconstructions of axial CT and MRA images.^[7] A 2D angiogram or CT or MRA may easily show a large vessel fenestration like those in the proximal basilar artery but the inadequate resolution to see delicate fenestrations of tiny vessel like those in ACoA.^[7]

Table 1: Fenestration of anterior communicating artery in different studies

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The internal carotid artery (ICA) divisions (upper and lower) develop in 4–5.7 mm (28–30 days) embryos.^[23] The primitive olfactory artery is made up of the upper division of ICA, which also forms middle cerebral and anterior choroidal arteries.^[24] Primordial olfactory artery contains two tributaries in 11.5–28 mm (41–48 days) embryos: the primary branch to nasal cavity and another branch reflects the subsequent continuation of ACA.^[24] The more medial artery and its similar one on other extremities are connected by plexiform conjunction at the conclusion of this phase. In this conjunction, the networking vessels progressively unite to create a single ACoA.^[25] Fenestration in the ACA-ACoA complex is caused by whole or partial persistence of arterial network between the bilateral ACAs.^[26]

Whether FIA contributes to the development of aneurysm is a matter of debate.^[3] According to a few studies, fenestration and aneurysm have been linked because of the unstable flow caused due to some defects in the middle layer of vessel wall.^[17] Related studies have revealed that FIA involves intravascular eddy currents, by disrupting the inner lining of the fenestration which weakens the outermost layer of blood vessels, which leads to an increase in the risk of brain aneurysm development.^[3],[27] In an additional research, FIA is associated with a greater prevalence of aneurysm due to the association of abnormality in the intermediate layer of arterial wall with an increase in hemodynamic pressure.^[28] Around one-third of the FIAs are structurally linked with aneurysms and most of these aneurysms are seen in ACoA complex. However, the relation between aneurysm and fenestration is unclear.^[3] Alternatively, the incidence of ACoA fenestration appears higher in studies including cases with aneurysm than those without it [Table 1]. The incidence of fenestration was low in the current study as compared to earlier studies probably due to the exclusion of cases of aneurysm.

Previous studies have found that fenestrations can occur in conjunction with several neurovascular pathologies other than aneurysms including dissections, dural fistulas, arteriovenous malformations, and ischemic strokes.^[7],[8] This is due to the fact that only individuals with suspected intracranial vascular disease undergo cerebral angiography. However, there is no conclusive evidence-linking fenestrations to neurovascular diseases. Furthermore, there is no association of fenestration with aneurysms and vascular diseases according to recent studies.^[7] Precise complicated anatomy should be recognized before endovascular or surgical treatment to prevent unexpected outcome and making treatment decision for aneurysms requires careful consideration of fenestration.^[15] The 3DRA implementation has significantly increased the resolution of brain vascular imaging, and thus, high-resolution pictures are now possible because of recent developments in 3DRA which plays a crucial part in treatment planning of cerebral aneurysms.^[1]

Conclusion

In CTA, the overall incidence of ACoA fenestration is low (0.95%) in Indian population. Fenestrations are uncommon, and thorough knowledge of such anatomical variations of cerebral vasculature is helpful for radiologists as well as neurovascular surgeons in treating complex neurovascular procedures.

Acknowledgment

I would like to express my sincere gratitude to the head of the Department of Anatomy and Radiology, JIPMER, for encouraging me to conduct this study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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