CASE 16615 Published on 18.02.2020

A rare case of basilar artery fenestration with anterior and posterior saccular aneurysms resulting in acute subarachnoid haemorrhage



Case Type

Clinical Cases


Chadwick Garner, MD, Tyler Diener, MD

Beaumont Hospital Dearborn - Radiology Department

18101 Oakwood Blvd

Dearborn, MI, 48124


39 years, female

Area of Interest Arteries / Aorta, CNS ; Imaging Technique Catheter arteriography, CT-Angiography
Clinical History

A 39-year-old female patient presented to the emergency department with a headache for two days. Non-contrast CT of the head demonstrated acute subarachnoid haemorrhage in the basal and prepontine cisterns with subtle intraventricular haemorrhage in the third and fourth ventricles. CTA was subsequently performed and demonstrated focal fenestration of the basilar artery with anterior and posterior projecting aneurysms.

Imaging Findings

Figure 1:  Computed tomography angiography (CTA) was performed and demonstrated focal fenestration of the mid-basilar artery with saccular anterior and bilobed posterior projecting aneurysms with the necks of the aneurysms located at the base of the fenestration (Fig. 1).

Figure 2a & 2b: The patient was evaluated by our neurointerventional team and subsequently underwent digital subtraction angiography for neurointerventional planning. Left vertebral artery injection demonstrated two aneurysms arising from the mid-basilar artery at the inferior aspect of the small basilar fenestration. The aneurysms were confirmed to be discrete and were not communicating with each other. The posterior projecting aneurysm with irregular/bilobed morphology measured 4.7 mm (width) X 4.2 mm (depth) X 2.5 mm (depth) with a 1.9 mm neck. The anterior projecting aneurysm with normal saccular morphology measured 3.0 mm (width) x 2.5 mm (depth) x 2.2 mm (depth) with a 2.2 mm neck (Figure 2).

Figure 3a & 3b: The posterior projecting aneurysm underwent endovascular coil placement with Micrusphere 10 (3mm x 5.4 cm Cerecyte) and Deltapaq 10 (2mm x 4 cm stretch-resistant coil). The anterior projecting aneurysm underwent endovascular coil placement with Micrusphere 10: (2 mm x 2.5 cm Cerecyte coil) and Deltapaq 10 (1.5 mm x 2 cm stretch-resistant coil) without residual filling demonstrated on post-coiling angiography (Fig. 3).


The term fenestration refers to a localised duplication of a vessel. Fenestration of the basilar artery has been reported to be as high as 6% in postmortem studies [1]. Basilar artery fenestration most frequently occurs in the proximal aspect with a typical extension of less than 5 mm [2,3,4]. The embryology of basilar artery formation has been described in the literature and results from the embryonic fusion of the longitudinal neural arteries to form the single basilar artery in the craniocaudal direction [5].  Fenestration is thought to occur when there is disruption of this fusion as well as that of the bridging arteries that connect the longitudinal arteries [1].

This case illustrates 1.5 mm mid-basilar fenestration with associated discrete anterior and posterior projecting saccular aneurysms. The clinical significance of a fenestrated basilar artery is unclear with the most common sequela to be aneurysmal dilatation thought to be from intrinsic wall defect on either side of the fenestration and haemodynamic stress [6]. Aneurysms tend to occur at branch points of the fenestration secondary to turbulent flow [7,8]. As with any aneurysms of the intracranial vasculature, there is a risk of rupture resulting in life-threatening intracranial haemorrhage. Here, we highlight an uncommon yet critical process that causes aneurysmal formation, which could result in life-threatening haemorrhage.

There can be a wide range of symptomatology with cerebral aneurysms depending on the location, size, and acuity of the aneurysm. Our patient presented with a severe headache and was found to have an acute subarachnoid haemorrhage.

Important imaging diagnostics to consider would be computed tomography angiography in the emergent setting to evaluate the intracranial vasculature. The fast image acquisition to evaluate the arterial anatomy is essential in a suspected aneurysmal rupture and assists in planning for potential neurointerventional management, typically accomplished with aneurysm coiling. 

It is essential to know the main cause of spontaneous acute subarachnoid haemorrhage is cerebral aneurysm rupture [9]. Prompt evaluation of the intracranial vasculature with computed tomography angiography and early consultation of neurointerventional services is of paramount importance for patient survival.

Written informed patient consent for publication has been obtained.

Differential Diagnosis List
Acute subarachnoid haemorrhage from basilar artery fenestration resulting in saccular aneurysm formation
Acute subarachnoid haemorrhage
Tuberculosis meningitis
Bacterial meningitis
Pseudo-subarachnoid haemorrhage
Final Diagnosis
Acute subarachnoid haemorrhage from basilar artery fenestration resulting in saccular aneurysm formation
Case information
ISSN: 1563-4086