Duplicated middle cerebral artery arising from the origin of the hyperplastic anterior choroidal artery that mimicked aneurysm on routine MR angiography

Abstract

We report a case of duplicated right middle cerebral artery that arose from the origin of the right hyperplastic anterior choroidal artery diagnosed by magnetic resonance angiography. To our knowledge, this is the first case of such a variation reported with magnetic resonance angiographic images. The internal carotid artery–hyperplastic anterior choroidal artery-duplicated middle cerebral artery junction was dilated and mimicking aneurysm. Partial maximum intensity projection images and volume-rendering images showed that it was not a saccular aneurysm but an infundibular dilatation. Careful observation of magnetic resonance angiographic images including its source images is important for detecting rare arterial variations. To identify an anomalous artery on magnetic resonance angiography, creation of partial maximum intensity projection images and volume-rendering images is valuable.

Introduction

Variations of the middle cerebral artery (MCA) include duplicated MCA, accessory MCA and fenestration.^1,2 The posterior communicating artery (PCoA) arises from the supraclinoid internal carotid artery (ICA) and is frequently larger than the P1 segment of the posterior cerebral artery (PCA). Such a PCA is described as fetal type. The junction of the ICA and PCoA is one of the common sites of cerebral aneurysm. The origin of the PCoA is frequently dilated in a triangular shape. When the maximum diameter of the origin of the PCoA is smaller than 3 mm and the trunk arises from the apex of the dilatation, it is described as infundibular dilatation or widening of the PCoA.^3,4 The infundibular dilatation is also seen at the origin of the anterior choroidal artery (AChA), and it is well known that the PCA rarely branches from the AChA, a variation of the AChA described as hyperplastic.⁵ The catheter angiographic prevalence of a hyperplastic AChA has been reported as 2.3%.⁶

We present a case of a duplicated MCA arising from the infundibular dilatation of a hyperplastic AChA that mimics a saccular aneurysm at the junction of the ICA and hyperplastic AChA. We believe this is the first report of such a variation diagnosed by magnetic resonance (MR) angiography. To identify and demonstrate this rare variation, we created both partial maximum intensity projection (MIP) and volume-rendering (VR) images.

Case report

A 71-year-old man with headache visited our hospital and underwent cerebral MR imaging and MR angiography for evaluation of cerebrovascular disease. He was examined using a 1.5-Tesla scanner (Magnetom Symphony; Siemens Medical Systems, Erlangen, Germany) and standard three-dimensional time-of-flight MR angiography protocol. We evaluated routinely obtained MIP images using the SYNAPSE (Fujifilm Medical Company, Tokyo, Japan) picture archiving and communication system and created partial MIP images and VR images to confirm the anomalous artery.

MR angiography showed an aneurysmal dilatation at the junction of the right ICA and possible PCoA (Figure 1). Hypoplasticity of the P1 segment of the right PCA suggested a fetal-type PCA. The bilateral superior cerebellar arteries arose from the PCAs. A partial MIP image (Figure 2) showed two arteries arising from the dilated right ICA–possible PCoA junction. The approximately 3 mm maximum diameter of the dilated segment indicated infundibular dilatation.

Figure 1.

Magnetic resonance angiography obtained using a 1.5-Tesla scanner.

Antero-posterior projection of maximum intensity projection image shows a slight protrusion at the right supraclinoid internal carotid artery (ICA), which suggests a saccular aneurysm at the junction of the ICA and posterior communicating artery (long arrow). A hypoplastic P1 segment of the right posterior cerebral artery (PCA) (short arrow) indicates a PCA of fetal type. The bilateral superior cerebellar arteries arise from the proximal P1 segments of the PCAs.

Figure 2.

Partial maximum intensity projection magnetic resonance angiographic image of the right carotid system including the posterior cerebral artery (PCA). Antero-posterior projection image shows two arteries arising from the aneurysmal dilatation. The long arrow indicates a PCA, and the short arrow indicates a duplicated middle cerebral artery.

Repeat MR angiography was performed using a 3-Tesla machine (Achieva 3.0 T TX Quasar Dual; Philips Medical Systems, Best, the Netherlands). A VR image (Figure 3) showed that the artery originating from the ICA was not a fetal-type PCA but a hyperplastic AChA. The distal segment of the right AChA was not identified on MR angiography probably due to low spatial resolution. Figure 4 presents a schematic illustration of the circle of Willis of this patient.

Figure 3.

Volume-rendering magnetic resonance angiographic image obtained using a 3-Tesla scanner. Postero-anterior projection image clearly demonstrates the relationship between the two arteries (long and short arrows) and dilatation of their common origin. This is not a saccular aneurysm but an infundibular dilatation. There are two posterior cerebral arteries (PCAs). Thus, the artery arising from the internal carotid artery is regarded as a hyperplastic anterior choroidal artery (AChA) rather than a fetal-type PCA. But unfortunately, the distal segment of the AChA cannot be identified probably due to low spatial resolution.

Figure 4.

Schematic illustration of the circle of Willis in infero-superior projection. The left is a normal subject, and the right is our patient. The hyperplastic anterior choroidal artery (AChA) shows infundibular dilatation at its origin, and the duplicated middle cerebral artery (MCA) arises from the dilated segment. The superior cerebellar artery (SCA) arises from the proximal P1 segment of the posterior cerebral artery (PCA). The duplicated right MCA arises from the origin of the hyperplastic AChA (arrow).

ICA: internal carotid artery.

Discussion

According to Padget,⁷ most adult arteries in the head region are recognisable in a stage 5 embryo of 16–18 mm length, and completion of the circle of Willis is observed in a stage 6 embryo of 20–24 mm length. Arterial variations may develop from failure of fusion or abnormal fusion during these early embryonic stages.

MCA variations include duplicated MCA, accessory MCA of proximal origin, accessory MCA of distal origin, early bifurcation of the MCA, fenestration of the MCA and duplicate origin of the MCA.^1,2,8 Figure 5 illustrates these variations. The duplicated MCA is classified in two types. Type A separates at the tip of the ICA, and type B separates between the tip of the ICA and the AChA.⁹ In our patient, the duplicated MCA arose from the ICA–hyperplastic AChA junction. But unfortunately, the distal segment of the right AChA was not identified on MR angiography. If digital subtraction angiography is performed, the presence or absence of the tiny AChA may be confirmed. If the distal segment of the AChA arises from this artery, it is confirmed as hyperplastic AChA.⁶ Embryologically, duplicated MCA cannot originate proximal to the AChA, because the AChA appears earlier in development. Fenestration and duplicate origin have been confused,⁸ and duplicate origin may also be confused with fenestration of the supraclinoid ICA.¹⁰ The duplicated MCA arises from the supraclinoid ICA, just proximal to the carotid bifurcation. To the best of the authors’ knowledge, this is the first report of a patient with a duplicated MCA that arises from the ICA–hyperplastic AChA junction. Extremely rarely, a saccular aneurysm is seen at the junction between the ICA and the duplicated MCA.^11,12

Figure 5.

Schematic illustration of several variations of the middle cerebral artery (MCA) in antero-posterior projection: 1, duplicated MCA; 2, accessory MCA of proximal origin; 3, accessory MCA of distal origin; 4, early bifurcated MCA; 5, fenestration of the MCA; 6: duplicate origin of the MCA.

The PCoA arises from the supraclinoid ICA and anastomoses with the PCA at the P1–P2 junction. The P1 segment of the PCA is frequently hypoplastic (so-called fetal-type PCA), as in our patient, and the PCoA is also frequently hypoplastic. The origin of the PCoA is frequently dilated (so-called infundibular dilatation). The points differentiating this variation from an aneurysm at the ICA–PCoA junction include its round or triangular shape without a neck, smaller maximum diameter than 3 mm and origination of the PCoA from its apex.^3,4 In our patient, we initially diagnosed that he had an infundibular dilatation of the right PCoA and development of the duplicated MCA from the dilated segment. However, we finally diagnosed that he had a hyperplastic AChA using a VR image obtained by a 3-Tesla machine, because the artery arising from the supraclinoid ICA did not anastomose with the P1–P2 junction of the PCA.

An anatomical study by Vlajković and colleagues¹³ revealed infundibular dilatation of the PCoA in 2.2% and aneurysms of the PCoA in 1.12% of adults. The absence of both in fetuses suggested that infundibular dilatation is not congenital but an acquired lesion. Rarely, a saccular aneurysm develops from the infundibular dilatation.⁴ Infundibular dilatation of the AChA is not as common as the PCoA. The MR angiographic prevalence of a hyperplastic AChA has been reported to be 0.55%.⁵

Conclusions

We present what we believe is the first report of a case in which a duplicated MCA arising from the origin of the hyperplastic AChA was diagnosed by MR angiography. Infundibular dilatation of the AChA was present. Both partial MIP images and VR images are useful for identifying rare cerebral arterial variations during interpretation of MR angiography.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Conflict of interest

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.