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Infraoptic Course of the Anterior Cerebral Artery: Case Report

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Although anomalies of the anterior cerebral artery (ACA)-anterior communicating artery (AComA) com- plex are commonly identified at imaging studies, an in- fraoptic ACA is extremely rare (1-4). In such cases, an anomalous vessel originates from the internal carotid artery (ICA) at the level of the ophthalmic artery, and then pursues an infraoptic and prechiasmatic path to supply the ACA. We describe a case of in which this anomaly coexisted with a ruptured middle cerebral artery aneurysm, and include the angiographic and magnetic resonance imaging findings.

Case Report

A 55-year-old woman in previous good health experi- enced the sudden onset of severe headache without fo- cal neurological deficits. CT scanning demonstrated he- morrhage in the left side of the basal cistern and left syl- vian fissure (Fig. 1), suggesting rupture of a left middle cerebral artery aneurysm. Angiography revealed a broad-based saccular aneurysm at the main division of the left middle cerebral artery (Fig. 2), and an anom- alous arterial branch, originating from the right ICA at the level of the ophthalmic artery, was also visible. A portion of its proximal segment contained an almost horizontal portion, suggesting that an anomalous ACA coursed below the ipsilateral optic nerve (Fig. 3). Its ini- tial course was medial, and it then turned superiorly to join the normally positioned AComA. The left A1 seg- ment was not hypoplastic. T2-weighted magnetic reso- nance imaging confirmed the infraoptic course of the proximal precommunicating tract (A1) under the ipsilat-

J Korean Radiol Soc 2002;47:565-568

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Infraoptic Course of the Anterior Cerebral Artery: Case Report

1

Myong Hee Seo, M.D., Ghi Jai Lee, M.D., Jae-Chan Shim, M.D., O-Ki Kwon, M.D.2, Young-Cho Koh, M.D.2, Ho Kyun Kim, M.D.

An infraoptic anterior cerebral artery (ACA) arising at a low bifurcation of the inter- nal carotid artery is a rare anomaly, of which about 33 cases have been reported to date, often in association with cerebral aneurysms. We describe a case involving an in- fraoptic ACA in which a ruptured middle cerebral artery aneurysm was also present.

Angiography revealed the presence of an abnormal solitary ACA, arising from the in- tracranial proximal internal carotid artery near the origin of the ophthalmic artery, and a contralateral middle cerebral artery aneurysm. Magnetic resonance imaging showed that the ACA passed below the ipsilateral optic nerve, anterior to the optic chiasm, to join the normally positioned anterior communicating artery above the optic chiasm.

Index words : Aneurysm, cerebral Arteries, MR

Arteries, abnormalities

1Department of Diagnostic Radiology, Inje University College of Medicine

2Department of Neurosurgery, Inje University College of Medicine Received November 9, 2002; Accepted November 22, 2002

Address reprint requests to : Ghi Jai Lee, M.D., Department of Radiology, Seoul Paik Hospital, Inje University College of Medicine, 2-85, Jur-dong, Chung-gu, Seoul 100-032, Korea.

Tel. 82-2-2270-0134 Fax. 82-2-2266-6799 E-mail: hongage@unitel.co.kr

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eral optic nerve, with the distal A1 tract anterior to the chiasm and positioned between the optic nerves, and the joining of bilateral ACAs above the optic chiasm was also visualized (Fig. 4). Next day, the left middle cerebral artery aneurysm was surgically clipped during pterional craniotomy.

Discussion

Anomalies of the anterior circle of Willis are quite commonly discovered at imaging studies but are usually

of little clinical significance. Aplasia or hypoplasia of the A1 segment, fenestration or duplication of the AComA, and the presence of three distal ACAs are frequently re- ported anomalies (4). An infraoptic ACA is an exceed- ingly rare anomaly, however, and one which-because of the high prevalence of associated aneurysms and surgi- cal planning-has important implications. It was first de- scribed, after discovery during an anatomic dissection, by Robinson in 1959 (5) and first demonstrated angio- graphically by Isherwood and Dutton (6). To date, about 33 cases, which came to light during autopsy or surgery,

Myong Hee Seo, et al: Infraoptic Course of the Anterior Cerebral Artery

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A B C

Fig. 3. Right internal carotid arteriogram AP (A), lateral (B), and oblique (C) views reveal an anomalous vessel (arrows) arising from the internal carotid artery at the level of the ophthalmic artery, which courses medially and then superoposteriorly to join the ante- rior communicating artery.

Fig. 1. Unenhanced CT scan shows hemorrhage in the left side basal cistern and the left sylvian fissure, suggesting the rupture of left middle cerebral artery aneurysm.

Fig. 2. Left internal carotid arteriogram reveals a broad-based saccular aneurysm at the main division of the middle cerebral artery.

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or at radiological imaging studies, have been reported.

In cases of unilateral infraoptic ACA, there is a slight right-sided predilection; bilateral anomalous ACAs (7) and an infraoptic ACA associated with a pituitary tumor (8) have also been reported.

From the bifurcation of the ICA, the ACA normally courses medially and often somewhat anteriorly to- wards the interhemispheric fissure, passing over the op- tic nerves and chiasm. In all reported cases, the infraop- tic course of the ACA began at a low bifurcation of the ICA, at the level of the ophthalmic artery or above. This anomalous ACA is of large caliber and is often associat- ed with contralateral A1 agenesis or hypoplasia (3). In our case, the caliber of the contralateral A1 was near normal. In a few cases, a hypoplastic ipsilateral supraop- tic A1 tract has been reported in association with an anomalous infraoptic A1 tract (9), and although this anomalous vessel is functionally equivalent to the A1 segment of the ACA, some authors thus prefer the term

“carotid-anterior cerebral artery anastomosis”to “anom- alous ACA”.

The embryogenesis of this anomalous ACA is contro- versial. Because a hypoplastic ipsilateral supraoptic A1 has been identified, and the anomalous vessel and the ophthalmic artery appear to share a common origin, some authors maintain that this anomaly is not a mis- placed A1 segment, but the persistence of an embry- ological vessel such as a variant of a primitive prechias- mal arterial anastomosis (5, 6) or primitive ventral oph- thalmic artery (10).

As with other variations in the circle of Willis, the prevalence of associated cerebral aneurysms is higher

(1, 11), and the cause is thought to be the hemodynamic stress borne by an asymmetric vessel in an incomplete or unbalanced circle of Willis (12, 13). The most com- mon site of an aneurysm is the ACA-AComA complex (3, 11) but they may arise anywhere within the circle of Willis, including the middle cerebral artery, as in our case.

In summary, an infraoptic ACA arising at a low bifur- cation of the ICA is a rare congenital anomaly originat- ing from the ICA at the level of the ophthalmic artery and passing below the ipsilateral optic nerve before as- cending between bilateral optic nerves to meet the con- tralateral ACA above the optic chiasm. Where surgery is being considered for either an aneurysm in the ACA- AComA complex or a pituitary tumor, preoperative recognition of this aberrant artery is important.

References

1. Spinnato S, Pasqualin A, Chioffi F, Da Pian R. Infraoptic course of the anterior cerebral artery associated with an anterior communi- cating artery aneurysm: anatomic case report and embryological considerations. Neurosurgery 1999;44:1315-1319

2. Given CA 2nd, Morris PP. Recognition and importance of an in- fraoptic anterior cerebral artery: case report. AJNR Am J Neuroradiol 2002;23(3):452-454

3. Odake G. Carotid-anterior cerebral artery anastomosis with aneurysm: case report and review of the literature. Neurosurgery 1988;23:654-658

4. Gomes FB, Duvjovny M, Umansky F, et al. Microanatomy of the anterior cerebral artery. Surg Neurol 1986;26:129-141

5. Robinson LR. An unusual human anterior cerebral artery. J Anat 1959;93:131-133

6. Isherwood I, Dutton J. Unusual anomaly of the anterior cerebral artery. Acta Radiol Diagn(Stockh) 1969;9:345-351

7. Klein SI, Gahbauer H, Goodrich I. Bilateral anomalous anterior J Korean Radiol Soc 2002;47:565-568

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A B C

Fig. 4. T2-weighted coronal (A) and oblique sagittal (B) magnetic resonance images show an anomalous anterior cerebral artery (ar- rows) passes below ipsilateral optic nerve (arrowheads) and ascends superiorly between bilateral optic nerves to join the normally positioned anterior communicating artery above the optic chiasm. Normal course of left anterior cerebral artery (curved arrow) is well demonstrated on T2-weighted coronal image at the level of the optic chiasm (C).

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cerebral artery and infraoptic aneurysm. AJNR Am J Neuroradiol 1987;8:1142-1143

8. Sheehy JP, Kendall BE, Thomas DGT. Infraoptic course of the ante- rior cerebral artery associated with a pituitary tumor. Surg Neurol 1983;20:97-99

9. Nutik S, Dilenge D. Carotid-anterior cerebral artery anastomosis:

case report. J Neurosurg 1976;44:378-382

10. Brismar J, Ackerman R, Robertson G. Anomaly of anterior cere- bral artery: a case report and embryologic considerations. Acta Radiol(Diagn) 1977;18:154-160

11. Fusimoto S, Murakami A. Anomalous branch of the internal carotid artery supplying circulation of the anterior cerebral artery.

J Neurosurg 1983;58:941-946

12. Milenkovic Z, Duric S, Stefanovic I, Igniatovic G, Babic M, Ivanov I. Multiple intracranial aneurysms and asymmetrical circle of Willis. Med Pregl 1995;48:32-35

13. Lee EH, Suh DC, Lee SI, Auh YH. Angiographic analysis of the cir- cle of Willis: comparison between normal and aneurysm groups. J Korean Radiol Soc 1999;40:197-203

Myong Hee Seo, et al: Infraoptic Course of the Anterior Cerebral Artery

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대한방사선의학회지 2002;47:565-568

전대뇌동맥의 시신경하 주행:증례 보고1

1인제대학교 의과대학 진단방사선과학교실

2인제대학교 의과대학 신경외과학교실

서명희・이기재・심재찬・권오기2・고영초2・김호균

전대뇌동맥이 내경동맥으로부터 낮게 분지하며 시신경 밑으로 주행하는 것은 매우 드문 기형으로 현재까지 세계적 으로 약 33예가 보고되었으며, 동맥류가 잘 동반되는 것으로 알려져 있다. 저자들은 파열된 중대뇌동맥류와 함께 동반 된 전대뇌동맥의 시신경하 주행 1예를 혈관조영술 및 자기공명영상 소견과 함께 보고하고자 한다.

수치

Fig. 2. Left internal carotid arteriogram reveals a broad-based saccular aneurysm at the main division of the middle cerebral artery
Fig. 4. T2-weighted coronal (A) and oblique sagittal (B) magnetic resonance images show an anomalous anterior cerebral artery (ar- (ar-rows) passes below ipsilateral optic nerve (arrowheads) and ascends superiorly between bilateral optic nerves to join the

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