Carotid-anterior cerebral artery anastomosis Case report STEPHEN NUT1K, M.D., PH.D., AND DOMENICO DILENGE, M.D.

Departments of Neurosurgery and Radiology, Centre Hospitalier Universitaire, University of Sherbrooke, Sherbrooke, Quebec ~" The angiographic and anatomical features of an anomalous communication between the intradural internal carotid artery and the anterior cerebral artery are described. Essential features of the anastomosis include an origin at, or close to, the origin of the ophthalmic artery, a course ventral to the ipsilateral optic nerve and anterior to the optic chiasm, and a termination near the anterior communicating artery. Although rare, the condition should be considered as an entity. The incidence of associated berry aneurysm and other congenital vascular anomalies is high. KEY WORDS 9 cerebral arteries, anomaly cerebral arteries, anterior 9 anenrysm

HE purpose of this presentation is to define the characteristics of a rare anomalous cerebral artery and to discuss some possibilities concerning its origin. The vessel originates at the internal carotid artery at the branching of the ophthalmic artery, passes inferior to the optic nerve, and ascends anterior to the optic chiasm to join the anterior cerebral artery (ACA) near, or at, the anterior communicating system. The angiographic features are striking, especially in the frontal projection. The anomaly is virtually unknown: there are only seven previously reported cases2-4,ca most of which have been described in such a way that the anomaly has not been adequately indexed.

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9 carotid artery, internal

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onset of headache, loss of consciousness, and an associated tonic-clonic convulsion. Examination revealed mild confusion, moderate neck stiffness, and early papilledema. The cerebrospinal fluid (CSF) was grossly bloody and had a xanthochromic supernatant.

Radiological Examination. Seven days after admission, bilateral carotid and left vertebral angiography was performed. A saccular aneurysm was found in the region of the anterior communicating artery (ACoA) (Figs. 1 and 2). Its long axis was directed upward and to the left. It filled only from the left carotid injection. The left carotid injection revealed the existence of an abnormal vessel branching from the intradural origin of the carotid siphon (Figs. 1 and 2). This vessel Case Report terminated in the region of the ACoA. It A 22-year-old woman was admitted to the followed an oblique path superiorly and neurology service 3 days after the sudden medially which was concave toward the left 378

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Carotid-anterior cerebral artery anastomosis

Fro. 1. Superimposed right and left common carotid angiogram. The left intradural internal carotid artery (arrowheads) has a more oblique course than the right. Its first angiographic branch (1) is an abnormal vessel which runs medially and dorsally to join the contralateral anterior cerebral artery in the midline at the presumed site of the anterior communicating artery which allowedfillingof some identical vessels on both right and left injections. There is an aneurysm (2) on the anomalous vesseljust to the left the anterior communicating region. The left middle cerebral artery (3) appears to be a direct continuation of the internal carotid.

and superiorly. On the oblique views, part of showed the disappearance of the vasospasm its course projected below the image of the and lumbar puncture revealed a pressure of optic canal. The aneurysm appeared to be 220 mm H~O. situated on this vessel 3 to 4 mm proximal to Operation. Surgery was performed on the the inferred site of the ACoA. The precom- 25th day following hemorrhage. The exposure municating segment of the left ACA had a was by a left frontotemporal craniotomy small caliber and was only faintly opacified because of the aneurysmal filling from the left (Fig. 2). There was absence of filling of the carotid and the origin of the aneurysm proxophthalmic arteries with each internal carotid imal to the anterior communicating artery. injection. Yet unilateral filling of each The anomalous artery was identified as it ophthalmic artery was seen with injection of appeared from beneath the optic nerve and the ipsilateral external carotid artery (Fig. 3). was followed to the aneurysm after the This filling seemed to be dependent on the removal of a small amount of the left gyrus middle meningeal arteries. rectus (Fig. 4). This vessel branched into three Neurosurgical consultation was obtained divisions which were thought to be left frontoon the eighth day following admission. polar, pericallosal and callosomarginal on Because the patient was drowsy, had evidence reinspection of the angiogram. The aneurysm of vascular spasm on arteriography per- originated at the trifurcation and had a neck. formed the day before, and had a CSF The vessel at the region of the junction of the pressure of 400 mm H~O, it was decided to trifurcation and aneurysmal origin appeared defer definitive surgery for 1 to 2 weeks. On to have a thinner wall than normal. The the 24th day postbleed, repeat angiography aneurysmal neck was clipped and methyl-

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Fic. 2. Selective left internal carotid arteriogram in lateral (upper left) anteroposterior (upper right), and transorbital oblique (lower right) views. A hypoplastic left anterior cerebral artery is identifiable (arrowheads). The anomalous vessel (1) is again seen. The anterior choroidal artery is seen originating distally on the internal carotid artery (3). Another unusual vessel is noted originating from the precavernous portion of the internal carotid artery (2). The course of this artery suggests that it may be the left anteroinferior cerebellar artery, a possibility strengthened by the fact that the anteroinferior cerebellar did not fill during the vertebral angiogram.

methacrylate was used to further reinforce tin. Angiography was repeated on the 17th the area. The anterior communicating artery, postoperative day and revealed no filling of the small normally positioned left precom- the aneurysm. municating ACA and the right ACA were not Discussion seen. Postoperative Course. The postoperative There are seven other cases in the literature course was uneventful except for a mild fever. in which the anomalous anastomosis is idenThis disappeared after the cessation of Dilan- tifiable. 2-~'6a These reports include autopsy 380

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Carotid-anterior cerebral artery anastomosis studies, 4,7 findings on arteriography, 2.3 and cases where angiography findings were confirmed at surgery for aneurysm? ,6 In all but two cases 2 information is given on the carotid circulation bilaterally. One case demonstrates the anomaly bilaterally? The anomalous vessel appears to replace the function of the proximal anterior cerebral artery. In all cases, it supplies the territory usually perfused by the ipsilateral ACA, and in three cases it supplied the majority of the anterior circulation bilaterally. 4,8,7 Regardless of this function, however, it should not be described as the ACA because, in our case and in two others, ',7 a normally-positioned hypoplastic proximal ACA is identified. Furthermore, its absence in the other cases is not definite because it is a conclusion based only on radiological findings or the limited dissection at surgery. Therefore, it is best to name the anomaly by the descriptive term "carotid-anterior cerebral artery anastomosis." A variety of other cerebrovascular anomalies have been noted in these cases which may be significant. The incidence of berry aneurysms seems high. An aneurysm was found in our case and in two others? ,8 Furthermore, Isherwood and Dutton 8 reported a case of subarachnoid hemorrhage which may have been caused by a ruptured aneurysm which did not fill on angiography? The ipsilateral ophthalmic artery had an abnormal origin in our case and in one other, ~ a finding which is interesting considering the proximity of the sites of origin of the anomalous vessel and the normal ophthalmic artery. Other vascular abnormalities found in these cases include carotid agenesis, 7 fused pericallosal artery, ~ and a possible variant of a carotid-basilar anastomosis in our case and in one other. ~ The origin of the anomaly is unknown. Isherwood and Dutton a suggested that it may be a variant of the prechiasmal anastomosis which forms part of the blood supply to the optic chiasm. 1 This anastomosis lies on the anterior and inferior border of the chiasm and is supplied by the internal carotid, ophthalmic, and anterior cerebral arteries. Variations in the size of the component vessels are known. It is possible that the vessel under discussion is an example of an extreme variation. This suggestion does not explain the genesis of the anomaly but does suggest the developmental potential for its oc-

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FIG. 3. Selective angiography of the left external carotid artery. The ophthalmic artery (arrows), some of its principal branches (black arrowheads) and the choroidalplexus outlining the ocular globe (open arrowheads) are opacified. The ophthalmic filling is via the medial branch of the middle meningeal artery (dotted arrows).

FIG. 4. Operative photograph taken through the left frontotemporal cramotomy. The proximal left intradural internal carotid artery (1) is seen. The anomalous anastomotic vessel (4) appears from below the left optic nerve (2) to pass between it and the right optic nerve (3). A metallic clip occludes the aneurysm which is obscured from view by the anomalous vessel. 381

S. Nutik and D. Dilenge References currence. Further indication of an embryological origin are the associated vascular 1. Dawson BH: The blood vessels of the human anomalies summarized above. optic chiasma and their relation to those of the The anomaly might be explained by the hypophysis and thalamus. Brain 81:207-217, persistence to the time of full development of 1958 a vascular anastomotic loop normally present 2. Decker K (ed): Clinical Neurorafliology. Shedadi W, translator. New York: McGrawonly in the embryo. The necessary charHill, 1966 acteristics of such a loop would be an anastomosis ventral to the optic nerve and an 3. Isherwood I, Dutton J: Unusual anomaly of anterior cerebral artery. Acta Radiol [Diagn] origin from the internal carotid or anterior 9:345-351 cerebral arteries. The exact sites of origin 4. McCormick WF: A unique anomaly of the infrom the parent vessel need not be exactly tracranial arteries of man. Neurology specified because of the potential for basal (Minneap) 19:77-80, 1969 arteries to migrate along parent vessels to ac- 5. Padget DH: The development of the cranial commodate to the changing form of the arteries in the human embryo. Contrib Embryol developing brain? Two embryonic anasto32:207-261, 1948 motic loops which have the necessary charac- 6. Teal JS, Rumbaugh CL, Segall HD, et al: Anomalous branches of the internal carotid teristics are suggested by the work of Padget? artery. Radiology 106:567-573, 1973 One possibility is the transitory communication between the primitive dorsal and ventral 7. Turnbull I: Agenesis of the internal carotid artery. Neurology (Minneap) 12:588-590, 1962 ophthalmic arteries. The other is the potential anastomosis between the primitive olfactory and primitive maxillary arteries. At present, Address reprint requests to: Stephen Nutik, there are insufficient data to help choose M.D., Ph.D., Department of Neurosurgery, Cenbetween these possibilities or to suggest other tre Hospitalier Universitaire, Universit6 de Sherhypotheses to explain the anomaly. brooke, Sherbrooke, Quebec.

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Carotid-anterior cerebral artery anastomosis. Case report.

The angiographic and anatomical features of an anomalous communication between the intradural internal carotid artery and the anterior cerebral artery...
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