Basilar bifurcation aneurysm

• A Systematic Review and Case Illustrations of Misdiagnosing Intracranial Aneurysms
• Thromboembolic Events in the Posterior Circulation After Flow Diversion-A Closer Look at Coverage of the Posterior Cerebral Artery
• A Case of Preoperative Diagnosis of Pulmonary Artery Aneurysm Resected by Segmentectomy
• Endovascular treatment of wide-neck bifurcation aneurysms using pCONUS2 HPC bridging device with single antiplatelet: A Case Series
• Assessing Radiation Exposure and Contrast Agent Utilization: A Comparative Analysis of the Woven EndoBridge Device and Stent-Assisted Coil Embolization for Managing Unruptured Wide-Neck Bifurcation Aneurysms
• Woven endo bridge device for recurrent intracranial aneurysms: A systematic review and meta-analysis
• "Stent-within-a-Stent" technique for the endovascular treatment of giant aneurysm of basilar artery bifurcation: A case report
• Initial Experiences with the Trenza Embolization Device for the Treatment of Wide-Neck Intracranial Aneurysms: A 12-Patient Case Series

AKA Basilar apex aneurysms, including basilar tip aneurysm and basilar artery-superior cerebellar artery (BA-SCA) aneurysms.

Basilar bifurcation aneurysm epidemiology.

The pathogenesis of basilar apex aneurysm (BAA) are still poorly understood. Embryologically, basilar apex anatomical disposition is formed by the fusion of both caudal internal carotid divisions on the midline. To compare basilar apex morphology by embryological classification among patients with BAAs, anterior circulation aneurysms (ACAs), and controls. Prospectively collected data of 47 consecutive patients with unruptured BAAs (42 females and five males), age- and gender-matched 47 patients with unruptured ACAs, and 47 controls without any aneurysms were analyzed. Based on embryology, basilar apex morphology was classified into symmetric cranial fusion (SCrF), symmetric caudal fusion, and asymmetric fusion type. Posterior communicating artery (Pcom) was classified into hypoplastic, adult, or fetal type. The asymmetrical Pcom was defined as bilaterally different type Pcom. The ACAs located at the anterior communicating artery (n = 18), paraclinoid portion (n = 12), middle cerebral artery (n = 8), anterior cerebral artery (n = 5), the top of internal carotid artery (n = 2), and anterior choroidal artery (n = 2). Compared with the ACA group and controls, smoking, asymmetrical Pcom (fetal and adult type), and SCrF type were more prevalent in patients with BAAs by residual analysis. The multinomial logistic regression comparative analysis demonstrated that SCrF type was associated with BAAs (vs. ACA group; odds ratio, 13; 95% confidence interval, 3.8-41 and vs. controls; odds ratio, 25; 95% confidence interval, 5.4-121). The assessment of basilar apex morphology may aid in the understanding of the pathogenesis of BAA and the prediction of BAA formation ¹⁾.

BA bifurcation aneurysms are significantly associated with patients' age, female sex, wider bifurcation angles, and smaller vascular diameter at the BA bifurcation ²⁾.

Wide-Necked Basilar tip Aneurysm

Bifurcation angle and aspect ratio are independent predictors for aneurysm rupture. Bifurcation angle, which does not change after rupture, is correlated with hemodynamic factors including inflow coefficient and WSS, as well as rupture status. Aneurysms with the hands-up bifurcation configuration are more prone to rupture than aneurysms with other bifurcation configurations ³⁾.

High flow conditions, characterized by large and concentrated inflow jets, complex and oscillatory flow patterns, and wall shear stress distributions with focalized regions of high shear and large regions of low shear, are associated with aneurysm rupture, especially for basilar tip aneurysms. The higher flow conditions in basilar tip aneurysms could explain their increased rupture risk compared with internal carotid bifurcation aneurysms ⁴⁾.

Most present with SAH indistinguishable from SAH due to anterior circulation aneurysmal rupture. Enlargement of the aneurysm prior to rupture may rarely compress the optic chiasm →bitemporal field cut (mimicking pituitary tumor), or occasionally may compress the oculomotor nerve as it exits from the interpeduncular fossa →oculomotor nerve palsy.

These aneurysms can cause a variety of clinical features, depending on their size and location, and may present with symptoms such as:

Headache: A sudden, severe headache is a common symptom of a basilar bifurcation aneurysm.

Vision problems: The aneurysm may press on the nerves that control vision, causing blurred vision, double vision, or loss of vision in one eye.

Cranial nerve dysfunction: The aneurysm may compress or damage cranial nerves, leading to facial weakness, hearing loss, difficulty swallowing, or difficulty speaking.

Nausea and vomiting: An aneurysm can cause pressure on the brainstem, leading to nausea and vomiting.

Loss of consciousness: In severe cases, a basilar bifurcation aneurysm may cause loss of consciousness, seizures, or coma.

Sensory and motor deficits: The aneurysm may press on the brainstem or other parts of the brain, leading to sensory and motor deficits such as numbness, tingling, weakness, or paralysis on one side of the body.

It is important to note that some people with a basilar bifurcation aneurysm may not experience any symptoms at all, and the aneurysm may only be detected incidentally on brain imaging studies.

May occasionally be seen on CT or MRI as round mass in region of suprasellar cistern. With SAH, tend to see blood in interpeduncular cistern with some reflux into 4th (and to a lesser extent, third and lateral) ventricle. Occasionally may mimic pretruncal nonaneurysmal SAH.

Dome usually points superiorly. Should evaluate flow through posterior communicating arteries (may require Allcock test) in case trapping is required. Need to assess the height of the basilar bifurcation in relation to the dorsum sella.

Critical angiographic features to assess: On angiogram or CTA:

1. general features

2. orientation: determines whether surgery is an option. Posteriorly pointing aneurysms obscure perforators which may be adherent to the aneurysm, making surgery more difficult.

3. patency of PCAs & SCAs

4. patency and size of p-comms

a) diameter of p-comm >1 mm is needed to support collateral flow (expert opinion)

b) to determine if the P1’s can be sacrificed

c) P-comm patency and size is important for endovascular treatment as a potential route for deployment of horizontally oriented stent extending from P1 to contralateral

d) which can facilitate temporary clipping, or sacrifice, or placement of stents.

5. height of the aneurysm relative to the posterior clinoid process which will affect the selection of surgical approach (the range of height of the posterior clinoid is 4–14 mm)

a) supraclinoidal: aneurysm neck >5 mm superior to posterior clinoid process

b) clinoidal: aneurysm neck within 5 mm of posterior clinoid process

c) infraclinoidal: aneurysm neck >5 mm inferior to posterior clinoid process

see Basilar bifurcation aneurysm treatment.

If the aneurysm cannot be treated with endovascular technique, then the surgical option can be considered. Overall mortality is 5%, and morbidity is 12% (mostly due to injury to perforating vessels) ⁵⁾.

A study aimed to report the retrograde technique of horizontal stenting through the PCoA using a Solitaire AB stent.

A self-expandable stent was deployed from one posterior cerebral artery to the opposite, across the neck of a ruptured wide-neck basilar apex aneurysm.

The technique allowed successful aneurysm embolization with coils in a 53-year-old woman.

Different from clipping, where the fetal-type PCoA may pose an obstacle, in endovascular treatment, the Solitaire AB stent provides an alternative route to the aneurysm. It is easy to navigate, being fully retrievable and repositionable, which enables accurate deployment ⁶⁾.

A 69-year-old male admitted for Basilar bifurcation aneurysm. Subarachnoid hemorrhage. ⁷⁾