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Logo of neuroradjThe Neuroradiology Journal
 
Neuroradiol J. 2016 August; 29(4): 277–279.
Published online 2016 March 31. doi:  10.1177/1971400916642629
PMCID: PMC4978323

An unusual variation of carotid-vertebrobasilar arteries: An anatomical case report

Abstract

Background and purpose

Having no obvious clinical symptoms and signs, it is difficult to find head and neck vascular variations without the aid of vascular imaging techniques.

Summary of case

A 66-year-old female patient underwent head and neck computed tomographic angiography examination. Her computed tomographic angiography examination revealed that the internal carotid artery directly migrated to the ophthalmic artery. Brain blood supply is provided by the vertebrobasilar artery independently.

Conclusion

To the best of the author’s knowledge, this is a very rare anatomical vascular variation of the head and neck found by computed tomographic angiography.

Keywords: Anatomical variation, carotid artery, vertebrobasilar artery, computed tomography angiography

Introduction

The human brain, as the most vital organ in human body, has complex and rich vascular networks, which provide oxygen and other essential nutrients.1 The brain’s vascular supply typically has relatively generous collateralisation, which is provided by the various anastomoses between the carotid and vertebrobasilar circulations by the circle of Willis (CoW).2 It has been shown that approximately 50% of the population carries a kind of variation in their CoW congenitally.3 The author presents a case in which the internal carotid artery (ICA) acts as an end artery supplying the ophthalmic artery (OphA). Cerebral blood supply is provided entirely by the vertebrobasilar artery. To our knowledge, this is the first case reported that has such complex vascular variations in relation to the carotid and vertebrobasilar artery.

Case report

A female patient, aged 66 years, two days prior to admission without apparent inducement, appeared to show slurred speech, dizziness and discomfort associated with walking instability. She had a history of hypertension for 10 years, and had been taking amlodipine for blood pressure (BP) control. The patient underwent a head and neck computed tomography angiography (CTA) examination using GE Lightspeed 64-slice spiral computed tomography. The neck CTA revealed the aortic arch convex from the right to the left sequentially issued into the common trunk of the bilateral common carotid artery (CCA), the left subclavian artery and the right subclavian artery. The right subclavian artery lies in the top left. The initial portion of the CCA is stretching and curving (Figure 1(a)). The bilateral vertebral arteries become obviously thicker, the average luminal diameter being 6.0 mm on the left and 5.7 mm on the right. The left and right ICA average luminal diameter measures 2.9 mm and 2.6 mm, respectively. The bilateral ICAs directly continue to the OphA without other apparent branches (Figure 1(b)). The head CTA reveals that the brain blood supply is solely provided by the vertebrobasilar artery. The basilar artery end is divided into two branches, the end of the left branch is divided into two branches, the posterior branch migrates into the posterior cerebral artery (PCA), the anterior branch end is divided into the anterior cerebral artery (ACA) and the middle cerebral artery (MCA) (Figure 1(c)). The right branch end is divided into two branches, the medial branch first issues into a posterior communicating artery (PCoA), then the end of it is divided into the ACA and the MCA. The lateral branch migrates to the right PCA, anastomosing with the aforementioned PCoA (Figure 1(d)). The terminal bifurcation and the left wall of the basilar artery each sees an aneurysm with a deep diameter and neck diameter of 3.7 mm, 4.3 mm and 3.4 mm, 3.1 mm, respectively.

Figure 1.
(a) The patient’s VR computed tomography angiography (CTA) shows that the aortic arch convex from the right to the left issues sequentially into the common trunk of the bilateral common carotid artery (CCA), the left subclavian artery and the ...

Discussion

This case of the patient’s brain blood supply is only provided by the vertebrobasilar artery, the CoW connected between the vertebrobasilar system. To meet the needs of brain blood supply, both sides of the vertebral artery are significantly thicker. The normal left vertebral artery luminal diameter is about 3.23 ± 0.57 mm and right 2.9 ± 0.47 mm,4 this case measures about 6.0 mm and 5.7 mm, respectively. Just as only serving the OphA, the ICA is finer than normal. The left ICA luminal diameter is shown to be about 2.9 mm and the right is about 2.6 mm in this case, both sides of the ICA measure 4.0 ± 0.4 mm in the general female population.5 The three main vessels originating from the aortic arch convex and their arrangement is significantly different from the normal population, the CCAs sharing the common trunk located at the top right.

The OphA is one of the major branches of the ICA, usually originating from the superomedial or the anteromedial part of the ICA within the intradural space.6 Other rare origins, such as the middle meningeal artery,7 the basilar artery,8 the ACA9 and superolateral origin,10 have also been described. For this patient, the OphA is the direct continuation of the ICA. To the best of our knowledge, this is the first case described in the literature with such rare vascular variations. Such a relatively larger ICA fully supplying the OphA as an end artery seems mismatched. Presumably, during embryonic development, part of the ICA above the OphA opening atresiaed congenitally. With the initial portion of the CCAs stretching and curving, two sides of the CCA sharing the common trunk from the aortic arch convex, the ICA being separated from the CCA, these anatomical structures happen to have made the ICA undergo three times of arterial BP dropping before continuing to the OphA.

Clinically this patient, with the exception of a decade-long refractory hypertension, is also suffering from other cardiovascular diseases such as coronary atherosclerotic heart disease and cerebral lacunar infarctions. The brain blood supply being entirely provided by the vertebrobasilar artery has alleviated the BP of the ICA. The carotid sinus baroreceptor is more sensitive to arterial BP variability of the OphA rather than the brain blood supply. Schlaich et al.11 have reported that carotid sinus baroreceptor function could be reset to buffer fluctuations in the BP, but would be damaged because of age and arterial disease. Has the baroreceptor function of this patient been damaged by age or arterial disease? If so, this may, to some extent, help to explain partly the reasons why the patient has suffered from refractory hypertension.

The CoW as a potentially collateral circulation has the function of regulating the blood distribution in the brain circulation. The CoW variations of this case will directly affect the occurrence, development and prognosis of vertebrobasilar artery diseases. The failure to recognise these vascular variations preoperatively and blindness to operate on one side of the vertebral artery will lead to fatal consequences as well as otherwise preventable iatrogenic injuries and complications. Under the action of hypertension, its risk for vertebral artery stenosis, occlusion, rupture or the formation of dissection was significantly increased. Due to lack of ICA involvement, once vertebral artery luminal stenosis has occurred, cerebral arterial perfusion is bound to decrease significantly. The probability of the occurrence of massive cerebral infarction is far greater than in the general population.

In addition to severe vascular variations, the patient is also faced with the risk of multiple basilar aneurysms. Once aneurysm rupture has occurred, the probability of vertebrobasilar artery stenosis or occlusion, due to spasm, would greatly increase. In denial of further treatment, this patient was discharged initiatively after speech disorders and high BP symptoms improved.

This variation about the vertebrobasilar and carotid arteries provided by the author just being a kind of variation or an unknown rare circulatory pattern of the human head and neck remains to be further confirmed.

This report has been approved by the institutional review board and received consent from the patient to publish it.

Conflict of interest

None declared.

References

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Articles from The Neuroradiology Journal are provided here courtesy of SAGE Publications