A rare embryologic variation: anterior communicating artery aneurysm associated with carotid-anterior cerebral artery anastomosis or infraoptic course of the anterior cerebral artery.

Aneurysms of the complex of the anterior cerebral artery are frequently associated with anatomic variations of the circle of Willis. We describe a case of aneurysmal rupture of the anterior communicating artery, a variant of the anterior cerebral artery. The aneurysm appeared to be situated on this vessel proximal to the infered site of the AcoA. Surgery was performed at the 6th day after hemorrhage. The anterior communicating artery aneurysm was clipped. The post operative course was unventful, with complete recovery. In our case, an extremely rare variation of the proximal tract of the anterior cerebral artery, i.e. an infraoptic course of the proximal precommunicating tract under the optic nerve, with the distal A1 tract anterior to the chiasm and positioned between the optic nerves, is presented.


Introduction
The purpose of this presentation is to defi ne the characteristic of a rare anomalous cerebral artery and to discuss some possibilities concerning its origin. Carotid-anterior cerebral artery anastomosis constitutes an anomaly of the anterior part of the arterial circle of the brain (Bassett, 1949;Besson et al. 1980;Bollar et al. 1988;Chioffi et al. 1997;Kessler, 1979;Kwak, 1980;Lasjaunias et al. 2001;Mercier et al. 1989;Yaşargil, 1984). The anterior cerebral a. arises a few millimetres above the emergence of the internal carotid from the cavernous sinus, at the usual level of the ophthalmic a. It travels medially, beneath the optic n., and then describes a curve with a superolateral concavity to arrive at the anterior communicating a. (Lasjaunias et al. 2001;Yaşargil, 1984). This variant is often associated with other cerebral vasculer anomalies, especially arterial aneurysm (Chioffi et al. 1997;Kessler, 1979;Kwak et al. 1980;Lasjaunias et al. 2001).
This anomaly was associated with a ruptured anterior communicating artery (AcomA) aneurysm. It is concluded that, for aneurysm surgery, careful angiographic evaluation and an understanding of the neurovascular relationships in the circle of Willis are essential for a successful postoperative course, especially when very rare vascular anomalies are treated.
This report describes a rare case of anterior communicating artery aneurysm associated with carotid-anterior cerebral artery anastomosis or infraoptic course of the anterior cerebral artery which was treated by surgical approach.

Case Report
A 35-year-old male patient admitted to our clinic suffering from headaches with vomiting and loss of consciousness. Examination revealed mild confusion, moderate neck stiffness, and early papilledema. Radiological examination: Computed Tomography (CT) revealed subarachnoid hemorrhage in the basal and sylvian cisterns. Angiography (Figs. 1a and 1b) documented an anterior communicating artery aneurysm; the angiogram also demonstrated a low bifurcation of the right internal carotid artery (ICA), fi lling of the distal part (A2) of both anterior cerebral arteries from an anomalous A1 tract arising the origin of the ophthalmic artery (Oph A). The right carotid injection revealed the existence of an abnormal vessel branching from the intradural origin of the carotid siphon (Figs. 1a and 1b). This vessel terminated in the region of the AcoA. It followed an oblique path superiorly and medially which was concave toward the right and superiorly. On the oblique views, part of its course projected below the image of the optic canal. The aneurysm appeared to be situated on this vessel proximal to the infered site of the AcoA. Operation: surgery was performed at the 6th day after hemorrhage. A right pterional craniotomy was performed. After the carotid and chiesmatic cisterns were opened, a low bifurcation of the ICA was observed. The anomalous artery was identifi ed as it appeared from beneath the optic nevre and was followed to the aneurysm after the proximal A1 segment coursed under the ipsilateral optic nerve and the distal A1 segment ran anterior to the chiasm. The anterior communicating artery aneurysm was clipped. The post operative course was unventful, with complete recovery. Postoperative CT scan was normal. The anomalous infraoptic proximal tract of the anterior cerebral artery was documented by magnetic resonance angiography (Fig. 2) and threedimensional CT angiogaphy after surgery. Follow-up documented the successful exclusion of aneurysm.

Discussion
Aneurysms of the complex of the ACA are frequently associated with anatomic variations of the circle of Willis (Chioffi et al. 1997;Kessler, 1979;Kwak et al. 1980;Lasjaunias et al. 2001). Although hypoplasia of the A1 tract and presence of three distal ACAs can be clearly recognized in preoperative angiograms other anatomic varıations, such a fenestratıons of the AComA are generally discovered only during surgery (Dawson, 1958;Gomes et al. 1986;Lasjaunias et al. 2001).
The ACA normally courses from the ICA bifurcation medıally and often somewhat anteriorly, toward the interhemıspheric fıssure, passing over the optıc nerves and chiasm (supraoptic course). In all cases observed the ınfraoptıc course of the A1 tract ıs associated wıth a low bıfurcation of the ICA, at the level of Oph A( just as it becomes intradural) or above (Chioffi et al. 1997;Lasjaunias et al. 2001). In our case and in others, the origin of the anomalous A1 tract is in common with that of the OphA, and this may have a precise embryological signifi cance.
Patients with a supraoptic course of the proximal tract of the ACA have exhibited a variety of symptoms, mostly resulting from ruptured associated AComA aneurysms and occasionally resulting from compression of the optic nevre or chiasm by the anomalous vessel. In our case, an extremely rare variation of the proximal tract of the ACA, i.e. an infraoptic course of the proximal precommunicating tract (A1) under the optic nerve, with the distal A1 tract anterior to the chiasm and positioned between the optic nerves, is presented.

Conclusion
The anomalous infraoptic course of the proximal anterior cerebral artery was associated wıth a low bifurcation of the ipsilateral internal carotid artery in this patient. The anterior cerebral a. arises a few millimetres above the emergency of the internal carotid from the cavernous sinus, at the usual level of the ophthalmic a. It travels medially, beneath the optic n., and then describes a curve with a superolateral concavity to arrive at the anterior communicating a. The recognition of this variant is very important for allows optimal surgical planning and forestalls misinterpreation of the individual cerebral vascular anatomic features and possible complications during surgery.

Disclosure
The authors report no confl icts of interest.