Rare Dilated Collateral Circulation from Accessory Meningeal Artery to Inferolateral Trunk: A Case Report

Abstract

The accessory meningeal artery (AMA) demonstrates various potential anastomoses with the external (ECA) and internal (ICA) carotid arteries. However, rarely does the AMA markedly dilate and compensate for ICA blood flow. A 52-year-old woman with nonspecific symptoms was diagnosed with multiple cerebral aneurysms and abnormal blood vessels observed on magnetic resonance angiography. Digital subtraction angiography revealed four aneurysms and anastomoses between the left AMA and inferolateral trunk (ILT). In addition, two sequential severe flexions were observed in the cervical portion of the left ICA. No ischemic lesions were detected on magnetic resonance imaging. In conclusion, we experienced a rare case in which the AMA-ILT anastomosis was highly developed. This case also presented with the unusual characteristics of an anomaly in the extracranial ICA and multiple aneurysms.

Introduction

When blood flow to the brain is reduced owing to stenosis or occlusion of the internal carotid artery (ICA), collateral circulation is achieved via the circle of Willis, ophthalmic artery, or leptomeningeal arterial anastomoses.¹⁾ The collateral circulation via the external carotid artery (ECA) is also reported.^2,3) However, few cases have been reported in which the accessory meningeal artery (AMA) extensively developed connections to resolve ICA blood flow deficiency, and these reports are limited to cases with ICA occlusion.⁴⁾ We encountered a rare case of a highly developed anastomotic pathway from the AMA to the ICA in a patient without an ICA occlusion.

Case Report

A 52-year-old woman with nonspecific symptoms underwent magnetic resonance angiography, which revealed multiple cerebral aneurysms and an abnormal blood vessel. She was referred to our hospital for intensive examination. Digital subtraction angiography (DSA) was performed. Aneurysms were identified at four locations: 1) right ICA-ophthalmic artery bifurcation, 2) left ICA paraclinoid, 3) left ICA cavernous portion, and 4) left ICA cervical segment. In addition, an ECA-ICA anastomosis had developed on the left side (Fig. 1). The anastomotic vessel originated from the internal maxillary artery, was confirmed to pass through the foramen ovale by multiplanar reconstruction (MPR) images, and was determined to be the AMA (Fig. 2). The expanded AMA merged with the ICA cavernous portion and was considered an anastomosis with the inferolateral trunk (ILT). Further, researchers confirmed that the ophthalmic artery branched independently from the ICA by MPR imaging (Fig. 3). In addition, a severe double flexion of the left ICA cervical portion was observed on cervical DSA (Fig. 4). No apparent stenosis in the lumens of the two flexions was confirmed, and ICA blood flow reached the intracranial region earlier than the AMA-ILT anastomosis. One aneurysm was located on the greater side of the distal flexion. No abnormalities, including ischemic changes, were detected on brain MRI. Subsequently, the patient underwent coil embolization for a right ICA-ophthalmic artery bifurcation aneurysm and was treated conservatively otherwise.

Fig. 1

Left oblique (A) and lateral (B) views of three-dimensional rotational angiography show the anastomosis from the internal maxillary artery to the internal carotid artery (solid arrows). The dashed arrow shows the middle meningeal artery. The solid arrowhead indicates two aneurysms in the internal carotid artery.

Fig. 2

Multiplanar reconstruction image (A: axial, B: sagittal) shows that the anastomotic vessel passes through the foramen ovale (open arrow).

Fig. 3

Multiplanar reconstruction image shows that the ophthalmic artery (open arrowhead) branches off from the internal carotid artery separately from the accessory meningeal artery (open arrow).

Fig. 4

Left cervical digital subtraction angiography (A) shows double flexion of the internal carotid artery and an aneurysm (solid arrowhead) on the greater side of the distal flexion. Three-dimensional computed tomography angiography (B) shows close-up images of distal and proximal flexion. Digital subtraction angiography in the early arterial phase (C) and 0.25 seconds later (D) shows that the contrast medium passing through the internal carotid artery reaches the intracranial vessels earlier than the accessory meningeal artery (solid arrows).

Discussion

The AMA is derived from the primitive stapes artery and originates from the medial branch of the internal maxillary artery. Various potential anastomoses are known to form with the ICA branches and the ECA intra- and extracranially.⁵⁾ In the intracranial artery, the AMA networked with the ILT below the lateral side of the cavernous sinus in the intracranial artery and anastomosed with the recurrent meningeal artery, artery of the foramen rotundum, and the cavernous sinus branch of the middle meningeal artery. In addition, around the pyramid, a potential anastomosis was found with the meningohypophyseal trunk, petrosal branch of the middle meningeal artery, and subarcuate artery of the anterior inferior cerebellar artery.

Researchers also reported some cases of blood flow supplied from the ECA to the ICA in cases of congenital ICA aplasia or acquired ICA occlusion, in which AMA is sometimes used as collateral circulation.^2,3) Tsutsumi et al. reported a case of a brain arteriovenous malformation in which blood was supplied from a dilated AMA to the ICA via the inferior cavernous sinus artery, which is a branch of the ICA.⁶⁾ The potential anastomotic pathway between the AMA and ICA may play an important role in collateral circulation in the event of insufficient or increased demand for ICA blood flow.

However, an AMA-ILT anastomosis is rarely dilated to supply adequate blood flow to the ICA. Numerous reports exist of collateral circulation in the event of ICA occlusion or stenosis, but in most cases, anastomosis via the circle of Willis or ophthalmic artery or leptomeningeal arterial anastomosis occurs.¹⁾ No reports are found in English journals of cases in which AMA-ILT anastomosis was highly developed with no shunt disease involvement or ICA occlusion.

The AMA-ILT anastomosis in this case may have existed since birth or may have developed as collateral blood circulation. In our case, continuous severe flexion of the extracranial ICA was observed as a characteristic anomaly. Severe flexion of blood vessels sometimes reduces cerebral blood flow. Additionally, researchers reported that 60° of kinking reduces blood flow by 40%, and 30° reduces blood flow by 60%.⁷⁾ However, in this case, although strong flexion occurred, no stenosis was observed in the tortuous portion. Furthermore, DSA confirmed that no delay occurred in the delivery speed of the contrast medium from the extracranial ICA to the intracranial region. In addition, the patient was asymptomatic and showed no prior ischemic changes on MRI. These suggest that blood flow to the brain was sufficient, thereby making it unlikely that this anastomosis was acquired. In addition, as mentioned above, it is rare for the AMA-ILT anastomosis to develop in an acquired manner as a collateral circulation. It is highly likely that this anastomosis was present from birth.

Regarding the cause of the severe flexions of blood vessels, the possibility exists that this was congenital; however, the presence of multiple coexisting aneurysms suggested the influence of a collagen disease, such as fibromuscular dysplasia.⁸⁾ In this case, no carotid findings, such as strings of beads, which are characteristic of fibromuscular dysplasia, were observed, and pathological diagnosis for fibromuscular dysplasia was not performed. Furthermore, a fully dilated collateral circulation can present with aneurysm-related complications.⁹⁾ This is related to the increase in flow through the collateral circulation and the change in blood flow dynamics. Therefore, continuing vigilant observation is necessary.¹⁰⁾

Conclusion

Herein, we presented a rare case in which an AMA-ILT anastomosis was highly developed and an unusual anomaly of the extracranial ICA and multiple aneurysms were observed.

Author Contributions

All authors contributed to the report conception and design. The first draft of the manuscript was written by Mizuka IKEZAWA and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Conflicts of Interest Disclosure

The authors declare that they have no conflicts of interest.

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