Basilar bifurcation aneurysm associated with internal carotid artery occlusion. Report of two cases

Two cases of subarachnoid hemorrhage caused by rupture of a basilar bifurcation aneurysm associated with occlusion of the internal carotid artery (ICA) at the neck are presented. Case 1, a 71-year-old female, was hospitalized in a coma. Angiography demonstrated occlusion of the bilateral ICA, collateral blood supply through the branches of the foramen rotundum or vidian artery from the maxillary arteries and right posterior communicating artery, and a saccular aneurysm at the basilar bifurcation. The patient died 1 month later following rerupture of the aneurysm. Case 2, a 64-year-old male, was hospitalized for drowsiness. Angiography showed occlusion of the right ICA, collateral blood supply through a tortuous artery (a vidian artery), and a large aneurysm at the basilar bifurcation. Posterior circulation supplied anteriorly through the right posterior communicating artery. The patient died 1 month later because of rerupture of the aneurysm. Laminar thrombosis of the right ICA and an anastomotic vessel, seemingly a branch of the foramen rotundum or a vidian artery, were demonstrated by autopsy. The combination of cerebral aneurysm and collateral circulation is extremely rare in cases of occlusion of the ICA. The two cases described here suggest that hemodynamic stress is an important factor in the formation of cerebral aneurysms.     

Persistent primitive hypoglossal artery with retrograde flow from the vertebrobasilar system: a case report

The persistent primitive hypoglossal artery (PPHA) is one of the pairs of arterial connections that exist in the human embryo between the developing anterior and posterior circulation. Normally the PPHA arises from the cervical internal carotid artery (ICA) and passes through the hypoglossal canal to join the caudal basilar artery (BA). In most cases the vertebral arteries (VA) are either hypoplastic or aplastic and the posterior communicating arteries (PComA) are absent; thus, the main supply to the posterior circulation comes from the internal carotid via the PPHA in an antegrade fashion. Atherosclerotic plaques in the ICA and PPHA present with ischemic symptoms of both the carotid and vertebrobasilar systems. We report a case of a 53-year-old female who presented with a transient episode of left lower extremity numbness and weakness. Work-up with computed tomography (CT) and magnetic resonance imaging (MRI) showed a small watershed infarct in the right middle cerebral artery (MCA)/posterior cerebral artery (PCA) territory. Diagnostic angiography revealed severe proximal stenosis of the cervical ICA and presence of a PPHA just above the stenosis with retrograde filling from the vertebrobasilar junction to the distal cervical ICA. The patient underwent a carotid endarterectomy with intraoperative EEG monitoring. Intraoperative blood flow measurements were made before and after endarterectomy showing evidence of reversal of blood flow to a normal antegrade fashion. The postoperative angiogram showed resolution of the right ICA stenosis and persistence of the PHA. To our knowledge this is the first case report of a PPHA exhibiting reversal of blood flow from the posterior into the anterior circulation. Awareness of this embryological anomaly and its interaction with acquired atherosclerotic disease will minimize misinterpretation of vascular diagnostic studies.     

A 10-year follow-up of extracranial–intracranial bypass for the treatment of bilateral giant internal carotid artery aneurysms in a patient with fibromuscular dysplasia: case report

Cervicocephalic fibromuscular dysplasia (FMD) is an idiopathic, non-inflammatory and non-atherosclerotic arteriopathy which usually affects small- and medium-sized cervical arteries distributed at the atlas and axis interspace. Few cervicocephalic FMD patients are associated with multiple intracranial aneurysms which may rupture or develop. So the authors describe a cervicocephalic FMD patient with a history of right oculomotor palsy in 2000. Angiography revealed bilateral internal carotid artery (ICA) aneurysms and a fusiform aneurysm in right vertebral artery. Typical “string-of-beads” phenomenon was observed in V2 segment of left vertebral artery. The right ICA giant aneurysm was treated by right ICA occlusion and superficial temporal artery (STA)-middle cerebral artery (MCA) bypass at that time. Five years later, the patient presented with paroxysmal weakness in right limbs. The subsequent angiography showed the enlargement of left ICA aneurysm. It was treated satisfactorily with left external carotid artery-saphenous vein-MCA bypass and left ICA ligation. During the long-term follow-up, the patient kept no neurological deficit and the angiography showed good patency of bilateral grafts and the lesions in bilateral vertebral arteries remained unchanged.     

A case of posterior cerebral artery aneurysm associated with idiopathic bilateral internal carotid artery occlusion: case report

BACKGROUND: Aneurysms of the posterior circulation are challenging lesions to neurosurgeons, despite improvements in microsurgical techniques and advances in skull base approaches. We present a rare case of a posterior cerebral artery (PCA)-posterior communicating artery (PcomA) junction aneurysm associated with bilateral internal carotid artery (ICA) occlusion successfully treated with an endovascular procedure. CASE DESCRIPTION: A 57-year-old female presented with sudden onset of severe headache and loss of consciousness. CT scan showed diffuse subarachnoid hemorrhage and acute hydrocephalus. The patient developed severe neurogenic pulmonary edema and shock. Although her neurogenic pulmonary edema did not resolve, she recovered from shock. However, her general condition was so critical and her vital signs so unstable, that direct surgery under general anesthesia was considered too risky. A cerebral angiogram showed complete occlusion of both internal carotid arteries without any Moyamoya vessels. A saccular aneurysm located at the right PCA-PcomA junction was seen. To obliterate the aneurysm and prevent rerupture, the patient underwent coil embolization via an endovascular approach under sedation with local anesthesia. The balloon remodeling technique was useful to prevent occlusion of parent arteries. Finally, four interlocking detachable coils (IDC) with a total length of 44 cm were used to completely obliterate the aneurysm using the balloon remodeling technique. The patient made a full recovery after treatment and the aneurysm remained obliterated 2 years after coil embolization. CONCLUSIONS: We emphasize the advantages of the endovascular approach for the patient in critical condition. We believe that this is the first report of a PCA-Pcom junction aneurysm associated with bilateral ICA occlusion without moyamoya disease.     

Ruptured dissecting aneurysm of the vertebral artery associated with occlusive internal carotid artery dissection--case report

A 64-year-old male presented with subarachnoid hemorrhage. Angiography showed a dissecting aneurysm of the right vertebral artery (VA), and severe stenosis of the right internal carotid artery (ICA). He was treated conservatively in the early stage. Repeat angiography showed enlargement of the dissecting aneurysm of the VA and partial resolution of the stenosis of the right ICA. Intraaneurysmal coil embolization with proximal coil occlusion was performed following a balloon occlusion test. The postoperative course was uneventful. Based on the neuroradiological findings, the stenotic lesion of the right ICA was considered to be due to dissection. Analysis of serial changes in dissecting lesions in the craniocervical arteries is important for the correct choice of treatment, especially in patients with multi-vessel dissections. The surgical options should be determined on an individual basis.     

Hemodynamic study of posterior circulation using hydraulic vascular model--critical stenosis of the vertebrobasilar artery and tolerance to occlusion therapy.

A hydraulic vascular model with glass and silicone tubes of the intracranial portion of the vertebro-basilar artery was used to determine the critical stenosis causing vertebrobasilar insufficiency, and the minimum diameter of the posterior communicating arteries (PComAs) necessary to tolerate therapeutic vertebrobasilar occlusion for unclippable aneurysms. The critical stenosis of one vertebral artery (VA) or basilar artery (BA) differed greatly depending upon the anatomical variations of the PComA and the posterior cerebral artery (PCA): 1.14 mm diameter when the artery supplies 80 ml/min to the cerebellum and brainstem only, 1.33 mm when 140 ml/min to these structures and one PCA, and 1.56 mm when 200 ml/min to these structures and both PCAs. The minimum PComA diameter to tolerate therapeutic occlusion depended largely upon the occlusion site: one PComA with 1.54 mm diameter for bilateral VA occlusion and 1.25 mm for BA occlusion distal to the branching of the superior cerebellar arteries. The total volume of collateral flow through both PComAs can be estimated by summing the squares of the diameters. These values cannot be applied rigidly to clinical cases, but are useful standards to evaluate the stenotic lesion or tolerance to occlusion.     

Flow reverse therapy for ruptured dissecting aneurysm of basilar trunk: case report

Treatment of ruptured dissecting aneurysm of basilar trunk (BADAN) has been controversial yet. We report a case of ruptured BADAN successfully treated with endovascular occlusion of the bilateral vertebral artery (VA) proximal to posterior inferior cerebellar artery (PICA), allowing retrograde flow via the posterior communicating arteries to basilar artery. A 58-year-old woman who had subarachnoid hemorrhage was treated with endovascular occlusion of the right VA in acute stage after ballon occlusion test (BOT) of the right VA. Because following BOT of the left VA showed conscious level down, left VA could not be occluded. Follow-up angiography after 26 days revealed regrowth of BADAN. So left VA occlusion was tolerable by BOT after 1 month, we performed endovascular occlusion of the left VA proximal to PICA. She discharged with no neurological deficit after 3 months. Postoperative angiograms 3 months after onset showed complete healing of the aneurysm. The follow-up MRA at 19 months showed no recurrence. We discussed the therapeutic strategy of ruptured BADAN. Flow reverse therapy of bilateral VA occlusion by endovascular method for ruptured BADAN is one of the effective therapy.     

A case of fibromuscular dysplasia associated with intra- and extracranial multiple aneurysms]

A case of fibromuscular dysplasia (FMD) with intra- and extracranial multiple aneurysms is reported. A 42-year-old woman was admitted to Kagawa Central Hospital with severe headache and stiffness of the neck. CT scan showed subarachnoid hemorrhage predominantly in the left side of the basal cisterns and hydrocephalus. Angiography at admission revealed marked stenosis and dilatation of the extracranial major arteries and multiple aneurysms in the lt. PCA, lt. ICA, bil. VA, and the lt. renal artery. String-of-beads appearance was also seen in the branches of the lt. external carotid artery. During the operation, the PCA aneurysm which has been diagnosed as the ruptured one, was found to arise from the posterior communicating artery itself. It was thus a so-called true posterior communicating aneurysm. The aneurysm was trapped by clipping the artery on both the ICA and the PCA sides. The giant aneurysm of the lt. ICA was successfully treated by lt. STA-MCA anastomosis and ligation of the lt. ICA. Postoperative angiography demonstrated no visualization of the aneurysm and total occlusion at the origin of the lt. VA that had been patent preoperatively. On histological examination, intimal and medial hyperplasia was seen in the aneurysmal wall and occipital artery biopsied at operation. There has been no report of FMD associated with multiple and very rare posterior communicating aneurysms. Wide involvement of vascular change and advance of arterial occlusion noted by serial angiography indicates that FMD is a disease in which pathology would be progressive in some cases.     

Angiographic analysis of the internal carotid-vertebrobasilar system with cerebral aneurysms--with special interest in the morphological aspect including so-called vascular anomalies

In a series of 704 aneurysm patients who were admitted to the Research Institute for Brain and Blood Vessels-AKITA during the last 9.5 years (from October, 1974 to March, 1983), angiographic features of the internal carotid-vertebrobasilar system and related vascular anomalies were analyzed with reference to the site of aneurysms. The age distribution was from 20 to 78 years (mean age 53 years) and the men to women ratio was 1:1.1. The total number of the aneurysms was 866. The site distribution of aneurysms consisted of 230 (27%) anterior communicating, 269 (31%) middle cerebral, 282 (38%) internal carotid, 54 (6%) anterior cerebral, 45 (5%) vertebrobasilar and 6 other arteries. More than one aneurysm were found out in 137 cases. The total number of performed cerebral angiograms was 1840, in which right carotid arterial angiograms were 652, left carotid 644 and vertebral 544. Angiographic features of the posterior communicating arteries (Pcom) with or without internal carotid-Pcom aneurysm were compared one side with the other, statistically revealing that the morphological factor of the Pcom did not play an important role in the development of the cerebral aneurysm at this portion. Anomalies of the posterior cerebral artery directly originated from the internal carotid artery were found in 9 cases, and three of them had the aneurysm at their origin. Anomalous carotid-basilar anastomoses were seen in 7 cases, namely 6 persistent primitive trigeminal arteries (2 of them were PTA variants) and one persistent primitive hypoglossal artery.(ABSTRACT TRUNCATED AT 250 WORDS)     

Complete neck clipping of internal carotid-posterior communicating artery aneurysms using bayonet-shaped aneurysm clips: technical note

Neck clipping for internal carotid-posterior communicating artery (IC-PC) aneurysms using standard straight, angled, or curved clip may result in remnant aneurysm neck. We describe complete neck clipping of IC-PC aneurysms using a bayonet-shaped clip. The bayonet-shaped clip is applied perpendicular to the long axis of the internal carotid artery (ICA), and the blades of the clip are inserted between the aneurysm neck and the ICA. Using the clip applicator, the clip is gradually rotated counterclockwise or clockwise for left or right ICA aneurysm, respectively, so that the distal and shank portions of the clip blade are located at the aneurysm neck in the posterior communicating artery (Pcom) and ICA, respectively. As a result, the distal flexure of the clip blade fits the junction of the ICA and Pcom. This technique was used in four patients with ruptured ICA aneurysms and five patients with unruptured ICA aneurysms. Postoperative cerebral angiography demonstrated no residual aneurysm neck and preservation of the Pcom in all patients. This technique is useful for cases of IC-PC aneurysm involving the origin of the Pcom.     

Successful treatment of a ruptured enlarged infundibular widening of the posterior communicating artery--case report

A 67-year-old female with a history of hypertension and cerebral infarction presented with subarachnoid hemorrhage (SAH) (Hunt and Kosnik grade 4). Brain computed tomography (CT) revealed a clot dominantly on the right (Fisher's classification Group 4). Cerebral angiography showed funnel-shaped widenings at the origins of the bilateral posterior communicating arteries. The maximum diameter of the widening was greater than 3 mm, so this widening was called an enlarged infundibular widening. Angiography showed a small bulge protruding posterolaterally from the wall of the right enlarged infundibular widening, and the right posterior communicating artery arose from the apex of the enlarged infundibular widening. Based on the findings of the brain CT and cerebral angiography, the diagnosis was SAH due to rupture of the right enlarged infundibular widening. Approximately 12 hours after the onset, the clot was evacuated through the right pterional approach. Bleeding from the small bulge of the right enlarged infundibular widening occurred intraoperatively, so a right-angled ring clip was applied parallel to the right internal carotid artery to obliterate the rupture point. Postoperatively, she was discharged without neurological deficit, and follow-up CT showed no other new infarction. We recommend clipping rather than wrapping or coating for similar cases of ruptured enlarged infundibular widening.     

Bilateral agenesis of internal carotid arteries

The authors present angiographic and computed tomographic demonstration of bilateral agenesis of internal carotid arteries. The patient was a seventy-six years old man who had been admitted to our hospital because of right hemisparesis and disorientation. In addition to the left chronic subdural hematoma, computed angiotomography showed the dilated basilar artery and dilated posterior communicating arteries. However, the bilateral internal carotid arteries were not recognized. Burr hole and irrigation were performed, then neurological deficits and symptoms were disappeared. Hematoma was 150 ml. Though axial transverse computed tomograms of base of skull demonstrated the absence of bilateral carotid canals. On aortography, the right common carotid artery and vertebral artery were supplied from the innominate artery and the left common carotid artery and vertebral artery were supplied from the left dilated subclavian artery. Bilateral retrograde brachial angiograms demonstrated the internal carotid circulation, which was supplied through bilateral dilated posterior communicating arteries. Basilar artery was also in a large caliber. Bilateral ophthalmic arteries were opacified from external carotid artery via the middle meningeal artery. Ten cases of bilateral agenesis of internal carotid arteries have been reported previously. The findings of angiograms and computed tomograms on the agenesis of bilateral internal carotid arteries were discussed. This anomaly is important on cerebral hemodynamics and embryology.     

Acute occlusion and recanalization of vertebral artery dissection after subarachnoid hemorrhage: usefulness of bilateral simultaneous vertebral angiography and basiparallel anatomic scanning-magnetic resonance imaging. Case report

A 41-year-old man presented with subarachnoid hemorrhage. Initial digital subtraction angiography showed occlusion of the right vertebral artery (VA), which recanalized immediately, and dissecting aneurysm on the distal part of the right VA. Basiparallel anatomic scanning (BPAS)-magnetic resonance (MR) imaging showed the morphology of the aneurysm clearly. Coil embolization of the entire affected artery was performed using bilateral vertebral angiography road mapping. Although acute occlusion of ruptured VA dissection may have the potential for natural healing, spontaneous recanalization seems to be hazardous because of rebleeding. In cases with acute occlusion of parent artery, BPAS-MR imaging and bilateral simultaneous vertebral angiography may give useful information.     

Bypass combined with embolization via a venous graft in a patient with a giant aneurysm in the posterior communicating artery and bilateral idiopathic occlusion of the internal carotid artery in the neck.

The authors describe the case of a patient with a symptomatic giant aneurysm of the posterior communicating artery (PCoA) associated with bilateral idiopathic occlusion of the internal carotid artery (ICA). The presence of severe tortuosity of the vertebral arteries (VAs), both at their origin from the subclavian artery and at the level of the third segment, impeded navigation of the catheter for embolization of the aneurysm with Guglielmi detachable coils (GDCs). A direct surgical approach was considered to be a high-risk procedure because of the bilateral occlusion of the ICAs and the size of the aneurysm. The following therapeutic strategy was therefore adopted: 1) balloon occlusion test of the left VA; 2) vertebro-vertebral bypass with saphenous vein graft to provide a pathway for subsequent embolization; 3) ICA-left middle cerebral artery bypass to ensure blood flow in the event that embolization resulted in closure of the PCoA; and 4) GDC embolization of the aneurysm via the posterior circulation graft to ensure complete exclusion of the lesion from the arterial circulation and preservation of the PCoA. At 3-month follow-up review the patient did not present with any neurological deficits; at 1-year control examination, magnetic resonance (MR) imaging and MR angiography both confirmed complete exclusion of the aneurysm and patency of the two bypasses.     

Bilateral segmental absence of the internal carotid artery with rete compensation associated with absence of basilar artery: case report

BACKGROUND: Bilateral ICA absence is a rare lesion. Collateral circulation to the middle and anterior cerebral arteries in the absence of one or both ICAs may develop transcranial anastomoses from the external carotid system, a so-called CRM. Very rarely, theses arterial channels are observed in humans. CASE DESCRIPTION: In the following case study, a 38-year-old man presented himself. He had a headache and scalp laceration after having had an accident. A right external carotid angiography identified anastomoses to distal intracranial vessel through the internal maxillary artery, but the intracranial vessels were only faintly visible. A right ascending pharyngeal arteriography showed an abnormal course and anastomoses with the intracranial vessel. The right ICA was absent. The left external carotid angiography demonstrated a network of tortous arteries in the region of the cavernous and petrous portion of ICA. The plexus of vessels on the left side communicated with the proximal part of the cavernous segment of the ICA. Both vertebral angiographies demonstrated a sudden diminution in caliber at the level of vertebrobasilar junction. There was an anomalous arterial collateral circulation originating from vertebral muscular and meningeal branch. There was also an absence of the basilar artery (BA). CONCLUSION: This is the first case with CRM associated with bilateral segmental ICA and BA absence. The cause of this bilateral segmental ICA and BA absence may be maldevelopment of vessel connective tissue or extracellular matrix.     

External carotid-basilar anastomosis: case report (author's transl)]

The occipital-vertebral anastomosis is one of the anastomotic channels between the external carotid system and the intracranial vessels. In this paper, we have reported a large, left external carotid-basilar anastomosis which was incidentally revealed in a patient with left hemiparesis due to arteriosclerotic occlusion of the right internal carotid artery. A 55-year-old man suddenly developed left hemiparesis without headache, unconsciousness or vomiting on the morning of January 15, 1973. When he was referred to our service on April 11, the noticeable neurological findings were left hemiparesis and left homonymous hemianopsia. The right carotid angiogram revealed occlusion of the internal carotid artery associated with collateral channels from the external carotid artery. Also a segment of the vertebral artery was visualized via the muscular branch of the occipital artery. In the left carotid angiogram, the posterior circulation was markedly visualized throught the left vertebral artery originating from the external carotid artery trunk. This anastomotic vessel had a large branch with constant caliber leading to the occipital fossa. But the posterior cerebral artery was directly visualized from the internal carotid artery without connection to the basilar artery. Repeated bilateral brachial angiograms revealed hypoplasis of the vertebral arteries. It was suggested that the persistent external carotid-basilar anastomosis might be constantly associated with hypoplasia or aplasia of the bilateral vertebral arteries.     

A vertebral artery tortuous course below the posterior arch of the atlas (without passing through the transverse foramen). Anatomical report and clinical significance

A vertebral artery (VA) coursing below the posterior arch of the atlas (C1) without passing through the transverse foramen of C1, combined with a tortuous course within the spinal canal has rarely been reported in the literature. This article describes a case encountered during an anatomical study of the far-lateral approach, and reviews its embryonic development and clinical significance. The suboccipital triangle was filled with numerous venous plexures. After exiting from the transverse foramen of C2, instead of passing upwards through the transverse foramen of C1, the VA turned directly medially towards the spinal canal. At the spinal canal, it first formed an angle downwards, then turned upwards, piercing and entering the lateral part of the dura at C1 level. The diameter of this VA seemed to be within its normal limits. The course of the contralateral (right) VA was normal but with a small caliber and mainly supplied the posterior inferior cerebellar artery (PICA); after PICA, it became much thinner and dysplastic, the basilar artery was mainly supplied by the left VA. The bilateral posterior communicating arteries were large in diameter but there was dysplasia of the P1 segment of the posterior cerebral arteries bilaterally. Marked tortuosity of the bilateral intracavernous internal carotid artery (ICA) was also found. We did not find any osseous abnormality in the occipito-axial region or of C1-C2 joint. An abnormal course of the VA should be kept in mind during exposure of the craniocervical junction, especially in the variety of lateral approaches; due to compression of the nerve roots or the spinal cord, this abnormal course of the VA could give rise to clinical symptoms, which could be resolved by microvascular decompression technique.     

Proximal ligation of the parent artery for symptomatic tandem stenosis of the extradural internal carotid artery: a case report

A 72-year-old man suffered blindness due to right central retinal artery occlusion. Cerebral angiography revealed tandem stenosis in the cervical, petrosal and cavernous portions of the right internal carotid artery (ICA). Blood flow from the vertebrobasilar artery via the right posterior communicating artery mainly perfused the right cerebral hemisphere. In addition, significant stenosis was observed in the left cervical carotid artery and the origin of the left vertebral artety. First, the patient underwent left carotid endarterectomy and vertebral artery to subclavian artery transposition. Two months later, ligation of the right ICA at its origin was performed. Postoperative course was uneventful and the patient has not experienced further ischemic events. We suggest that proximal ligation of the parent artery is a useful procedure for medically-refractory extradural ICA stenosis when surgical direct revascularization and percutaneous transluminal angioplasty cannot be performed.     

Spontaneous middle cerebral artery occlusion with moyamoya-like vessels associated with contralateral middle cerebral artery aneurysm; a case report]

A case of spontaneous middle cerebral artery occlusion with moyamoya-like vessels associated with contralateral middle cerebral artery aneurysm is reported. A 23-year-old male was admitted to our hospital with complaints of severe headache and vomiting. On admission CT scan demonstrated subarachnoid hemorrhage with high density in the left Sylvian fissure and suggested a ruptured left middle cerebral artery aneurysm. Carotid angiograms demonstrated a left middle cerebral artery aneurysm and an occlusion of the right middle cerebral artery at its origin with moyamoya-like vessels. There was no occlusion or stenosis in the bilateral intracranial internal carotid arteries. Furthermore, bilateral vertebral angiograms were also normal. The aneurysm was successfully clipped. The postoperative course was uneventful and the patient was discharged with no neurological deficit. So far as we could ascertain, there have been only 21 cases reported previously of spontaneous middle cerebral artery stenosis or occlusion with moyamoya-like vessels. According to angiographic studies and transcranial Doppler ultrasound findings, we are more inclined to believe that hemodynamic changes secondary to arterial occlusion lead to the formation and growth of aneurysms of the contralateral middle cerebral artery.     

A case showing the infraoptic course of the anterior cerebral artery associated with anterior cerebral artery aneurysm

A ruptured anterior cerebral artery aneurysm with anomalous right infraoptic course of the anterior cerebral artery (ACA) was reported. A 40-year old male was admitted because of SAH episode, and computerized tomography (CT) on the day of admission revealed hemorrhage in both Sylvian and interhemispheric fissures. Four-vessel angiography was performed on the same day. A saccular aneurysm was demonstrated in the region of the anterior communicating artery (ACoA), and anomalous artery, which originated from the intradural right carotid artery at the level of the right ophthalmic artery was found to be running medially and superiorly. It supplied the bilateral callosomarginal arteries and the unpaired pericallosal artery. The fenestration of the vertebral artery, duplication of bilateral superior cerebellar arteries, and an occipital artery arising from the right internal carotid artery at the C3 level were found. Surgery was performed on the first day of admission, and the anterior interhemispheric approach was selected. The anomalous branch of the right ICA ran beneath the right optic nerve, ascended between the optic nerves, and supplied the ACoA system. The left hypoplastic A1 segment entered the ACoA. However, the right A1 segment could not be found. The aneurysmal neck, situated between the bilateral callosomarginal arteries and the unpaired pericallosal artery, was clipped with Sugitas curved clip. The postoperative course was uneventful and a follow-up angiograph revealed successful obliteration of the aneurysm.