Anatomical variations in the circle of Willis on magnetic resonance angiography in a south Trinidad population

Abstract

Objectives: This article seeks to determine the prevalence of a complete circle of Willis (CoW) and its common morphological variations in a south Trinidad population, while also investigating the influence of gender, age, and ethnicity on CoW morphology.

Methods: A prospective, descriptive, cross-sectional study was done on the magnetic resonance images for consecutive patients who had a brain MRI/magnetic resonance angiography at a tertiary health institution in south Trinidad between October 2019 and September 2020. Patients with significant cerebrovascular disease and/or a history of prior neurosurgical intervention were excluded.

Results: A complete CoW was seen in 24.3%, with more complete circles observed in younger participants (≤45 years) and Afro-Trinidadians. No gender predilection for a complete CoW was demonstrated. The most common variations in the anterior and posterior parts of the circle were a hypoplastic anterior communicating artery (8.6%, n = 13) and bilateral aplastic posterior communicating arteries (18.4%, n = 28), respectively.

Conclusions: Significant variations exist in the CoW of a south Trinidad population with a frequency of complete in 24.3%, and more complete circles in younger patients and Afro-Trinidadians. Gender did not influence CoW morphology.

Advances in knowledge: Structural abnormalities in the CoW may be linked to future incidence of cerebrovascular diseases and should therefore be communicated to the referring physician in the written radiology report. Knowledge of variant anatomy and its frequency for a particular populations is also required by neurosurgeons and neuro-interventional radiologists to help with preprocedural planning and to minimize complications.

Keywords: Trinidad; Trinidad and Tobago; anatomical variations circle of Willis; circle of Willis; magnetic resonance angiography; magnetic resonance imaging; neuroradiology; stroke.

Figure 1.

Schematic diagram demonstrating a complete circle of Willis. Abbreviations: RT = right; LT = left; ICA = internal carotid artery; MCA = middle cerebral artery; ACA = anterior cerebral artery; ACoA = anterior communicating artery; PCA = posterior cerebral artery; PCoA = posterior communicating artery; BA = basilar artery.

Figure 2.

Axial maximum intensity projection magnetic resonance angiography image demonstrating a complete circle of Willis.

Figure 3.

Flowchart demonstrating the study exclusion criteria and final study sample size.

Figure 4.

Pie chart demonstrating the incidence of a complete, partial, and incomplete circle of Willis in a south Trinidad population referred for head MRI/MRA at the San Fernando General Hospital between October 1, 2019 and September 30, 2020.

Figure 5.

Bar graph demonstrating the frequencies of variations observed in the anterior part of the circle of Willis.

Figure 6.

Bar graph showing the frequencies of variations observed in the posterior part of the circle of Willis.

Figure 7.

Horizontal bar graph showing the frequencies of complete circles observed in the different age groups.

Figure 8.

Axial maximum intensity projection magnetic resonance angiography images demonstrating variants seen in the posterior part of the circle of Willis in our population: (A) bilateral aplastic PCoA; (B) unilateral aplastic left PCoA; (C) bilateral hypoplastic PCoA and (D) unilateral hypoplastic left PCoA. Abbreviation: PCoA = posterior communicating artery.

Figure 9.

Axial (A and B) and coronal (C) maximum intensity projection magnetic resonance angiography images demonstrating anterior communicating artery variations seen in our study: (A) absent ACoA; (B) hypoplastic ACoA; and (C) fenestrated ACoA. Abbreviation: ACoA = anterior communicating artery.

Figure 10.

Axial maximum intensity projection magnetic resonance angiography images demonstrating variations seen in the A1 segment of the ACA in our population: (A) absent A1 segment of the right ACA with both ACAs arising from the opposite ICA (white arrow); (B) hypoplastic A1 segment of the left ACA. Abbreviation: ACA = anterior cerebral artery.