Cerebral arterial fenestrations associated with intracranial saccular aneurysms

Supraclinoid Internal Carotid Artery Fenestration with Associated Aneurysm: Case Report and Literature Review

Fenestration of the supraclinoid internal carotid artery (ICA) is extremely rare and may occasionally be associated with saccular aneurysms; nevertheless, the natural history remains unclear. The authors reviewed the cases of fenestration of the supraclinoid ICA and evaluated the clinical characteristics and angioarchitecture with particular focus on the incidence for aneurysm development and rupture. Previously reported 24 cases and 1 new case from our institute were examined for the presence of aneurysms (including size and presence of bleb) leading to subsequent subarachnoid hemorrhage (SAH). Furthermore, 16 cases with sufficient information were classified into one of the three types according to the developmental condition of fenestration and fusion site: Type A (developed fenestration in which the ICA appears to duplicate [two cases]); Type B (hypoplastic fenestration fused to the ICA at the origin of the posterior communicating artery [Pcom] [six cases]); and Type C (hypoplastic fenestration fused to the Pcom itself or appeared to be a duplicated Pcom [eight cases]). In type A, the two cases had an aneurysm (100%), one of which caused SAH (50%). In type B, all six cases had an aneurysm (100%), and one of five led to SAH (20%) (one case lacked information regarding SAH). In type C, five of the eight cases had an aneurysm (62.5%), with no SAH (0%). The result suggested that the extent of development of fenestration and the location of fusion are related to the incidence of aneurysms and risk for rupture.

Endovascular management of a ruptured aneurysm associated with distal PICA fenestration

Fenestrations are rare but well-known arterial anatomic variations in which a segment of artery divides into two parallel channels that reunite distally. Although fenestrations as such are asymptomatic, they have gained clinical significance because of their association with aneurysms and other intracranial vascular pathologies. Here we present a 35-year-old woman with history of sudden severe occipital headache and vomiting. Imaging revealed a ruptured aneurysm in the distal posterior inferior cerebellar artery arising from one of the limbs of the fenestration. The aneurysm was successfully managed by coiling, and the patient made complete recovery without neurological sequelae.

Aneurysms Arising From the Fenestrated Middle Cerebral Artery

Intracranial artery fenestration is segmental duplication of the lumen into 2 distinct channels and is known to have a low angiographical incidence of 0.3 to 0.9%. Intracranial artery fenestration is frequently associated with aneurysms, and aneurysms arising at the site of fenestrated middle cerebral artery (MCA) is extremely rare. To our best knowledge, there are only 10 such patients have been reported. Herein, the authors describe the 11th case of aneurysm arising from the fenestrated MCA. As the characteristics of fenestrated MCA aneurysms has not been well determined until now, these interesting patients are investigated and summarized.

Vascular Anomalies of Posterior Fossa and Their Implications

Posterior fossa houses very vital and sensitive structures namely midbrain, pons, medulla, and cerebellum. These structures are irrigated by vertebral, posterior inferior cerebellar, anterior inferior cerebellar, and superior cerebellar arteries. Parts of brain located in posterior fossa control important parts of body so any variation pertaining to stenosis, atresia, hypoplasia, fenestration, agenesis, and duplication in the arteries supplying these parts alter the irrigation pattern culminating into various morbid and mortal neurologic disorders. Therefore, a sound understanding and thorough knowledge of posterior circulation vascular variant anatomy builds the foundation for the accurate diagnosis and appropriate management of neurovascular ischemic and hemorrhagic diseases of posterior fossa. To aid in addressing these complex neurologic disorders and neurosurgical treatment to be carried out successfully, updating and consolidating the knowledge of all the variations/insults of these arteries becomes essential. Therefore, review study has been carried out.Literature search was carried out using databases, including Scielo, Scopmed, Medline, PubMed, and Wiley online library. Papers containing original data were selected and secondary references retrieved from bibliographies. Search terms used were posterior fossa, anomalies of vertebral, posterior inferior cerebellar, anterior inferior cerebellar, and superior cerebellar arteries.The study will be of paramount importance to angiographers in interpreting angiographs, neurologists in diagnosis and treatment of neurologic disorders, and neurosurgeons in performing surgery in posterior fossa and craniovertebral region particularly dealing with tumors and vascular malformations.

Intracranial Arterial Fenestration and Risk of Aneurysm: A Systematic Review and Meta-Analysis

BACKGROUND

Previous studies have been inconsistent regarding risk for intracranial aneurysm related to intracranial arterial fenestration. We conducted a meta-analysis to examine the association between intracranial arterial fenestration and risk of aneurysm.

METHODS

We performed a systematic review of PubMed and Embase through August 2017 for potentially relevant articles. Summary odds ratios with 95% confidence intervals were pooled using a random-effects model.

RESULTS

Of 446 articles found, 7 were selected for meta-analysis. Pooled odds ratios revealed an increased risk of aneurysm owing to fenestration of 1.50 (95% confidence interval, 0.61-3.71; P = 0.38). Subgroup analyses based on the population presenting with various indications suggested that pooled odds ratios indicated a significant increase in risk for aneurysm of 2.43 (95% confidence interval, 1.04-5.69; P = 0.04).

CONCLUSIONS

Our findings indicate that intracranial arterial fenestration may be associated with increased risk for aneurysm formation.

Vertebral Artery Fenestration

Fenestration of the vertebral artery is a rare vascular anomaly that has been observed at autopsy and on angiography. It is most commonly seen in the extracranial segments of the vertebral artery. This congenital anomaly can arise during multiple different stages of embryological development of the vertebral artery. The clinical significance is unclear, but multiple studies have reported association with other vascular anomalies. Awareness of vascular anomalies is crucial to avoid iatrogenic injuries during endovascular diagnostic and therapeutic interventions. Here, we present a case of a patient with an intracranial vertebral artery fenestration that was identified during work-up for a foramen magnum mass.

Cerebral arterial fenestrations

Arterial fenestrations are an anatomic variant with indeterminate significance. Given the controversy surrounding fenestrations we sought their prevalence within our practice along with their association with other cerebrovascular anomalies. We retrospectively reviewed 10,927 patients undergoing digital subtraction angiography between 1992 and 2011. Dictated reports were searched for the terms "fenestration" or "fenestrated" with images reviewed for relevance, yielding 228 unique cases. A Medline database search from February 1964 to January 2013 generated 304 citations, 127 cases of which were selected for analysis. Cerebral arterial fenestrations were identified in 228 patients (2.1%). At least one aneurysm was noted in 60.5% of patients, with an aneurysm arising from the fenestration in 19.6% of patients. Aneurysmal subarachnoid hemorrhage or non-aneurysmal subarachnoid hemorrhage were present in 60.1% and 15.8%, respectively. For the subset of patients with an aneurysm arising directly from a fenestration relative to those patients with an aneurysm not immediately associated with a fenestration, the prevalence of aneurysmal subarachnoid hemorrhage was 66.7% vs. 58.6% (p = 0.58). Fenestrations were more often within the posterior circulation (73.2%) than the anterior circulation (24.6%), though there was no difference in the prevalence of aneurysms within these groups (61.1% vs. 60.7%, p = 1.0). Cerebral arterial fenestrations are an anatomic variant more often manifesting at the anterior communicating arterial complex and basilar artery and with no definite pathological relationship with aneurysms.

Ruptured saccular aneurysm arising from fenestrated proximal anterior cerebral artery : case report and literature review

The aneurysm arising from fenestrated proximal anterior cerebral artery (ACA) is considered to be unique. The authors report a case of a 59-year-old woman who presented with a subarachnoid hemorrhage (SAH) secondary to a ruptured aneurysm originating from the fenestrated A1 segment of right ACA. The patient had another unruptured aneurysm which was located at the right middle cerebral artery bifurcation. She was successfully treated with surgical clipping for both aneurysms. From the previously existing literatures, we found 18 more cases (1983-2011) of aneurysms associated with fenestrated A1 segment. All cases represented saccular type of aneurysms, and 79% of the patients had SAH. There were three subtypes of the fenestrated A1 aneurysms depending on the anatomical location, relative to the fenestrated segment. The most common type was the aneurysms located on the proximal end of fenestrated artery (82%). Azygos ACA and hypoplastic A1 were frequently accompanied by the aneurysm (33% and 31%, respectively), and multiple aneurysms were shown in three cases (16%). Considering that fenestrated A1 segment is likely to develop an aneurysm, which has high risk of rupture, early management may benefit patients with aneurysms accompanied by fenestrated proximal ACA.

Endovascular repair of ruptured aneurysm arising from fenestration of the horizontal segment of the anterior cerebral artery: case report

A 50-year-old man presented with an aneurysm arising from a fenestration of horizontal portion (A(1)) of the anterior cerebral artery manifesting as subarachnoid hemorrhage. Coil embolization was conducted and the aneurysm was occluded easily. Most reported cases of these types of aneurysms underwent direct surgery. Aneurysm arising from the A(1) fenestration is rare, but the present case shows that coil embolization can be an effective treatment modality. Three-dimensional rotational angiography and aneurysmography were helpful to characterize this complicated vascular structure.

Fenestration of supraclinoid internal carotid artery and associated aneurysm: embryogenesis, recognition, and management

OBJECTIVE

Fenestration of internal carotid artery (ICA) is extremely rare and may be associated with aneurysms arising from the fenestrated segment. Here we report two cases with successful surgical clipping of associated saccular aneurysms, and we systematically review the 12 previously reported cases.

METHODS

In one case of 39-year-old female patient, the aneurysm and fenestration were found incidentally in the course of a workup for headaches and a thyroid nodule. In the second case, a 32-year-old female patient, the aneurysm was associated with subarachnoid hemorrhage in the setting of suspected postpartum eclampsia. In both instances the fenestration involved the supraclinoid ICA, and the aneurysm arose from the duplicated segment proximal to the origin of the posterior communicating artery. The aneurysms were more proximal than typical posterior communicating artery aneurysms, and fenestration was suspected by rotational three-dimensional angiography, and confirmed at surgery.

RESULTS

In both instances the aneurysm was approached via an extended pterional craniotomy. In one case, partial anterior clinoidectomy was necessary, along with decompression of the optic nerve canal for optimal exposure of the aneurysm neck. Clip reconstruction was successful, obliterating the aneurysm and preserving ICA patency.

CONCLUSIONS

ICA fenestration should be considered when one analyzes ventral supraclinoid ICA aneurysms. In these and other reported cases, aneurysm is generally amenable to surgical clipping despite broad neck incorporating the fenestrated arterial segment.

Endovascular coil embolization for ruptured kissing aneurysms associated with A1 fenestration

Background:

Fenestration of intracranial arteries is a rare anomaly, and is frequently associated with cerebral aneurysms. In this paper, we report rare kissing aneurysms associated with A1 fenestration.

Case Description:

A 71-year-old woman presented with subarachnoid hemorrhage. Diagnostic digital subtraction angiography revealed two saccular aneurysms at the proximal junction of a fenestration and posterior aspect of the fenestration that appeared to be ‘kissing’ each other. Emergent endovascular coil embolization was performed.

Conclusion:

Kissing aneurysms associated with fenestration of the horizontal segment in the anterior cerebral artery are rare, and have not been reported. During treatment of such specific types of aneurysms by endovascular treatment, three-dimensional rotational digital subtraction angiography was very useful for deciding the appropriate working angles.

Concomitant dual origin and fenestration of the left vertebral artery resembling dissection

Dual origin and fenestration of the vertebral artery (VA) are very rare anomalies. Understanding of these variations, however, is important because they can be misdiagnosed as a VA dissection. A 42-year-old woman presented with motor weakness and sensory disturbance of the right upper extremity. Radiologic evaluations showed ectatic change in the right VA and an arteriovenous fistula between the right VA and the vertebral vein. We decided on endovascular occlusion of the proximal right VA and its fistulous portion. During the endovascular procedure, we had misunderstood the dual origin and fenestration of the VA as a dissection. Thus, failure to recognize these anomalies might result in unnecessary anticoagulation or therapeutic intervention. Clinicians should be alert to such VA variations when making a diagnosis and when planning any intervention or surgery involving the proximal VA.

Ruptured aneurysm arising from the distal end of a proximal a(1) fenestration : case report and review of the literature

A 75-year-old female presented with subarachnoid hemorrhage. Angiography revealed a partial duplication (fenestration) in the proximal A(1) segment and a ruptured aneurysm at the distal end of A(1) fenestration. This congenital anomaly accompanying an aneurysm was associated with duplicated ipsilateral middle cerebral artery (MCA). Congenital defect of the arterial wall and hemodynamic factors at the fenestrated A(1) are considered to play a significant role in the development of this aneurysm. The present case is peculiar because not only the ruptured A(1) aneurysm was related with the anterior and middle cerebral artery duplication but also the location of A(1) fenestration and the origin of A(1) aneurysm in a fenestration are quite unusual.

Three-dimensional angiographic demonstration of plexiform fenestrations of the proximal anterior cerebral artery associated with a ruptured aneurysm

A rare case of ruptured aneurysm associated with multiple A(1) fenestrations resembling plexiform network was demonstrated by 3D angiography. A 56-year-old female presented with a ruptured aneurysm in the A(2) segment of the left distal anterior cerebral artery associated with the right A(1) fenestration. The ruptured aneurysm was occluded with surgical neck clipping via interhemispheric approach without neurological deficit. Plexiform fenestrations of the right distal A(1), opposite side to the left ruptured A(2) aneurysm, were clearly visible on postoperative 3D angiography. Our case may strongly support the theory described by Paget, namely that a remnant of the plexiform anastomosis between the primitive olfactory artery and A(1) segment is the source of such fenestration.

A rare anomaly of the anterior communicating artery complex hidden by a large broad-neck aneurysm and disclosed by three-dimensional rotational angiography

Double fenestration of the anterior communicating artery (ACoA) complex associated with an aneurysm is a very rare finding and is usually caused by ACoA duplication and the presence of a median artery of the corpus callosum (MACC). We present a patient in whom double fenestration was not associated with ACoA duplication or even with MACC, representing therefore, a previously unreported anatomic variation. A 43 year old woman experienced sudden headache and the CT scans showed subarachnoid haemorrhage (SAH). On admission, her clinical condition was consistent with Hunt and Hess grade II. Conventional digital subtraction angiography (DSA) was performed and revealed multiple intracranial aneurysms arising from both middle cerebral arteries (MCA) and from the ACoA. Three-dimensional rotational angiography (3D-RA) disclosed a double fenestration of the ACoA complex which was missed by DSA. The patient underwent a classic pterional approach in order to achieve occlusion of both left MCA and ACoA aneurysms by surgical clipping. The post-operative period was uneventful. A rare anatomical variation characterised by a double fenestration not associated with ACoA duplication or MACC is described. The DSA images missed the double fenestration which was disclosed by 3D-RA, indicating the importance of 3D-RA in the diagnosis and surgical planning of intracranial aneurysms.

Fenestration of the Middle Cerebral Artery Detected by MR Angiography

Unlike fenestration of the posterior cerebral arterial circulation, fenestration of the anterior cerebral arterial circulation has not been well described. We investigated the location and configuration of fenestration of the middle cerebral artery (MCA) detected by magnetic resonance (MR) angiography. We found 6 fenestrations of the MCA among cranial MR angiography images obtained from about 2,000 patients during the past 9 years at our institution using either of two 1.5T imagers. All images were obtained by the three-dimensional time-of-flight technique. Maximum-intensity projection images in the horizontal rotation view were displayed stereoscopically. All 6 fenestrations had small slit-like configurations, five located at the proximal M1 segment, the other, at the middle M1 segment. No associated aneurysm was found. Although MCA fenestration is extremely rare and cerebral artery fenestration usually has no clinical significance, an aneurysm can arise at the proximal end of the fenestration. Thus, recognizing MCA fenestration is important when interpreting cranial MR angiograms.

Imaging the vertebral artery

Although conventional intraarterial digital subtraction angiography remains the gold standard method for imaging the vertebral artery, noninvasive modalities such as ultrasound, multislice computed tomographic angiography and magnetic resonance angiography are constantly improving and are playing an increasingly important role in diagnosing vertebral artery pathology in clinical practice. This paper reviews the current state of vertebral artery imaging from an evidence-based perspective. Normal anatomy, normal variants and a number of pathological entities such as vertebral atherosclerosis, arterial dissection, arteriovenous fistula, subclavian steal syndrome and vertebrobasilar dolichoectasia are discussed.

Microsurgically critical anomaly of the anterior communicating artery complex during the pterional approach to a ruptured aneurysm: double fenestration of the proximal A2 segments

A 50-year-old man presented with a ruptured aneurysm of the anterior communicating artery (ACoA) complex anomaly with the neck of the aneurysm located in the upper ACoA. The right pterional approach was performed 2 days after admission. Retraction of the frontal lobe exposed the lower half of the ACoA complex consisting of the origins of the bilateral A2 segments, and the apparent neck of the aneurysm was clipped. However, further exposure of the bilateral A2 segments revealed double fenestration of the proximal A2 segments, a subtype of duplication of the ACoA accompanied by a bridging artery between the upper and lower ACoA. The limited visualization of this ACoA complex anomaly with an aneurysm had led to the proximal origin of the bridging artery being mistaken for the neck of the aneurysm. Such double fenestration of the proximal A2 segments is a microsurgically critical anomaly of the ACoA complex, because the bridging artery mimics the neck of an aneurysm when visualized by the pterional approach.

Aneurysm and fenestration of the azygos anterior cerebral artery--case report

A 78-year-old female suffered sudden onset of nausea and headache. Computed tomography demonstrated diffuse subarachnoid hemorrhage. Cerebral angiography demonstrated an aneurysm arising from the right A1 segment of the azygos anterior cerebral artery, and the hypoplastic left A1. A right frontotemporal craniotomy was performed to obliterate the aneurysm by neck clipping. Surgical exploration found the fenestration of the right A1 and showed that the aneurysm had originated from the bifurcation of the fenestrated A1 and a small perforating artery arising from the fenestration. This unusual combination of an aneurysm associated with a fenestration of the right A1 and contralateral A1 hypoplasia may have been caused by local hemodynamic stress.

Aneurysm originating from the fenestration of the posterior cerebral artery: case report

OBJECTIVE AND IMPORTANCE

A rare case of an aneurysm arising at the fenestration of the P2 segment of the posterior cerebral artery is reported.

CLINICAL PRESENTATION

A 37-year-old man presented with severe headache and disturbance of consciousness. Computed tomographic scanning showed diffuse subarachnoid hemorrhage. Cerebral angiography revealed an aneurysm at the fenestration of the P2 segment of the right posterior cerebral artery. The aneurysm was located at the middle portion of the lower trunk of the fenestration. An unruptured arteriovenous malformation was incidentally found in the right thalamus.

INTERVENTION

A right frontotemporal craniotomy with orbitozygomatic osteotomy was made, and the aneurysm was successfully clipped. One year after the operation, gamma knife surgery was performed for the right thalamic arteriovenous malformation.

CONCLUSION

This is the first reported case of an aneurysm originating from the middle portion of a fenestrated posterior cerebral artery.

Ruptured vertebrobasilar junction aneurysm associated with basilar artery fenestration

A case of a ruptured saccular aneurysm arising from the proximal portion of a partially duplicated basilar artery in a 36-year-old woman is reported. CT and lumbar puncture confirmed subarachnoid haemorrhage. Cerebral angiography detected a vertebrobasilar junction aneurysm associated with basilar artery fenestration. The patient underwent successful clipping and coating of the aneurysm by a right lateral suboccipital osteoclastic approach. Embryological development, pathogenesis, diagnostic and therapeutic difficulties of this vascular malformation are discussed in this report.

Pictorial review: magnetic resonance angiography of arterial variants at the Circle of Willis

As intracranial MR angiography becomes more widely used and spatial resolution improves, anomalies at the Circle of Willis which have been previously well described on angiographic studies and anatomic dissections will become more frequently appreciated by MR angiography. Recognition of these variants is important to avoid confusion of the anomalies with aneurysms, evaluate collateral pathways in the intracerebral circulation, and enhance pre-operative planning in patients undergoing surgery at the skull base. In this review, we illustrate several of the more common types of anomalies at the Circle of Willis and discuss the possible clinical significance of each.

A ruptured aneurysm at the distal end of the basilar artery fenestration associated with multiple fenestrations of the vertebrobasilar system: case report

BACKGROUND

An aneurysm at the fenestrated basilar artery usually arises at the proximal end of the fenestration, with few exceptions. We failed to reveal any case of aneurysm at this site associated with multiple fenestrations of the vertebrobasilar system.

CASE REPORT

This 62-year-old male was admitted to our hospital 1 day after a sudden onset of headache. CT scan showed subarachnoid hemorrhage, and angiogram revealed an aneurysm at the distal end of the fenestrated basilar artery in association with two other fenestrations of the vertebrobasilar system. The limb of the basilar artery fenestration was trapped tightly with one clip through the transcondylar approach. Postoperative course was uneventful, and postoperative angiogram showed complete disappearance of the aneurysm.

CONCLUSION

An extremely rare case of an aneurysm at the distal end of the fenestrated basilar artery in association with multiple fenestrations of the vertebrobasilar system is reported. The coexistence of vertebral artery fenestration and the fenestration of the vertebrobasilar junction may give a clue to the mechanism of occurrence of basilar artery fenestration.

Aneurysmal subarachnoid hemorrhage in a patient with bilateral A1 fenestrations associated with an azygos anterior cerebral artery. Case report and literature review

Fenestration of the proximal anterior cerebral artery (A1 segment) is a rare occurrence. This vascular anomaly is often associated with aneurysms and other abnormalities. The current article describes the case of a 33-year-old man who presented with a subarachnoid hemorrhage secondary to a ruptured aneurysm originating from the proximal end of an A1 fenestration. This patient also had a contralateral A1 fenestration as well as an azygos anterior cerebral artery. This is the first report of such an unusual vascular anatomy. The literature is reviewed and possible embryological mechanisms are discussed.

The layered fabric of cerebral artery fenestrations

BACKGROUND AND PURPOSE

Intravascular bridges, resulting from developmental anomalies of brain arteries, are now better known as arterial fenestrations. Their tendency to develop aneurysms, similar to arterial bifurcations, makes their anatomy and microstructure important for study.

METHODS

Six segments of artery, each including a fenestration (five from the vertebrobasilar junction and one from the middle cerebral artery), were pressure distended, fixed, and sectioned. We made three-dimensional orientation measurements of smooth muscle and collagen, stained to enhance their birefringence, using the polarized light microscope.

RESULTS

The general contour of the fenestrations is streamlined with a thickened layered subendothelium at the trailing or distal edge, structurally similar to the region of convergence of major brain arteries. Defects of the medial layer were found at both proximal and distal edges of all the fenestrations. Results included regional mean orientations of individual layers, with circular SDs. The medial layer was found to be coherently aligned perpendicular to the direction of blood flow, with a mean circular SD of 12 degrees. The adventitia was less coherent (mean circular SD, 16 degrees) with the same average orientation, and the multilayered subendothelium had layers of obliquely oriented fibers with a wide range of coherence for individual fiber groups. Layers of the side regions were analogous to those in segments of brain artery and differed significantly from the proximal and distal edges of the fenestration structure.

CONCLUSIONS

The plasticity of form of the fenestrations at both the proximal and distal edges is in response to hemodynamic forces and is analogous to branching regions of brain arteries. Medial defects, a common feature in both brain arteries and fenestrations, may predispose the arterial fenestration to aneurysm formation.

Vertebrobasilar junction fenestration associated with dissecting aneurysm of intracranial vertebral artery

BACKGROUND

Vertebrobasilar junction fenestration is considered to be a subtype of fenestration of the proximal basilar artery, which has been described only in autopsy cases. The fenestration associated with a dissecting vertebral aneurysm is extremely rare.

CASE DESCRIPTION

A 47-year-old man presented with subarachnoid hemorrhage. The four-vessel angiogram showed a fusiform dilatation with an intimal flap of the left vertebral artery distal to the origin of the posterior inferior cerebellar artery and a fenestration at the vertebrobasilar junction, in which a small limb of the fenestration arising from the distal portion of the left vertebral artery bridged the proximal basilar trunk, while another limb had a large diameter showing the same diameter as the basilar artery. The dissecting aneurysm was treated with body clipping by directly clipping the ruptured portion of the aneurysm via a suboccipital approach in an early operation 48 hours after the ictus. The patient had a good recovery and returned to his work. He is well at a 5-year follow-up.

CONCLUSIONS

The relevant angiographic features of the vertebrobasilar junction fenestration and the surgical treatment of such associated aneurysms are discussed.

Supraclinoid internal carotid artery fenestration with an associated aneurysm. Case report

The case of an aneurysm occurring at the site of fenestration of the supraclinoid portion of the left internal carotid artery (ICA) is reported. A 37-year-old woman presenting with subarachnoid hemorrhage was found to have bilateral ICA aneurysms at the level of the posterior communicating arteries (PCoA's). The patient underwent right-sided craniotomy with uneventful clipping of the right PCoA aneurysm, and attempted clip placement on the contralateral left ICA aneurysm. The follow-up angiogram revealed a residual dome on the left ICA aneurysm, which was noted to originate at the proximal end of a fenestration of the left supraclinoid ICA. This represents the third reported case of fenestration of the intracranial ICA associated with an aneurysm. Intracranial artery fenestrations and their embryological origins are also reviewed.