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basilar_bifurcation_aneurysm

Basilar bifurcation aneurysm

Epidemiology

Pathogenesis

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).

Rupture risk

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).

Clinical features

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 fossaoculomotor nerve palsy.

Diagnosis

CT/MRIscan

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.

Angiography

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

Treatment

Outcome

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).

Case reports

A 45-year-old female patient who presented sudden mental confusion characterized by disorientation in time, space, and person. Investigative acute cerebral magnetic resonance imaging revealed diffusion restriction in the left posterior cerebral and superior cerebellar arteries. The clinical and cardiologic investigations revealed no abnormalities, but computed tomographic angiography and digital arteriography revealed a low-riding basilar bifurcation aneurysm and a very small aneurysm in the right internal carotid artery. The wide neck precluded coil embolization, and the appropriate stent was not covered by our public health insurance. Considering the young age, surgical treatment was proposed. Microsurgical clipping was performed using the right pre-temporal approach. In this two-dimensional video, we show the steps to reach the low-riding basilar bifurcation aneurysm neck. The positioning, transzygomatic pterional craniotomy, intradural anterior clinoidectomy, and posterior cavernous sinus opening are shown, and the surrounding anatomy is illustrated 6).


Wainberg et al., present the case of a 45-year-old female patient who presented sudden mental confusion characterized by disorientation in time, space, and person. Investigative acute cerebral magnetic resonance imaging revealed diffusion restriction in the left posterior cerebral and superior cerebellar arteries. The clinical and cardiologic investigations revealed no abnormalities, but computed tomographic angiography and digital arteriography revealed a low-riding basilar bifurcation aneurysm and a very small aneurysm in the right internal carotid artery. The wide neck precluded coil embolization, and the appropriate stent was not covered by our public health insurance. Considering the young age, surgical treatment was proposed. Microsurgical clipping was performed using the right pre-temporal approach. In a two-dimensional video, they show the steps to reach the low-riding basilar bifurcation aneurysm neck. The positioning, transzygomatic pterional craniotomy, intradural anterior clinoidectomy, and posterior cavernous sinus opening are shown, and the surrounding anatomy is illustrated 7).

References

1)
Matsukawa H, Kamiyama H, Noda K, Ota N, Takahashi O, Shonai T, Tokuda S, Tanikawa R. Embryological basilar apex disposition as a risk factor of basilar apex aneurysm. J Clin Neurosci. 2018 Dec;58:79-82. doi: 10.1016/j.jocn.2018.10.004. Epub 2018 Oct 13. PubMed PMID: 30327221.
2)
Zhang XJ, Gao BL, Li TX, Hao WL, Wu SS, Zhang DH. Association of Basilar Bifurcation Aneurysms With Age, Sex, and Bifurcation Geometry. Stroke. 2018 Jun;49(6):1371-1376. doi: 10.1161/STROKEAHA.118.020829. Epub 2018 May 3. PubMed PMID: 29724891.
3)
Rashad S, Sugiyama SI, Niizuma K, Sato K, Endo H, Omodaka S, Matsumoto Y, Fujimura M, Tominaga T. Impact of bifurcation angle and inflow coefficient on the rupture risk of bifurcation type basilar artery tip aneurysms. J Neurosurg. 2018 Mar;128(3):723-730. doi: 10.3171/2016.10.JNS161695. Epub 2017 Mar 3. PubMed PMID: 28298037.
4)
Doddasomayajula R, Chung B, Hamzei-Sichani F, Putman CM, Cebral JR. Differences in Hemodynamics and Rupture Rate of Aneurysms at the Bifurcation of the Basilar and Internal Carotid Arteries. AJNR Am J Neuroradiol. 2017 Mar;38(3):570-576. doi: 10.3174/ajnr.A5088. Epub 2017 Feb 16. PubMed PMID: 28209576.
5)
Drake CG. Management of Cerebral Aneurysm. Stroke. 1981; 12:273–283
6) , 7)
Wainberg RC, da Costa MDS, Marchiori M, Soder RB, de Campos Filho JM, Netto HLD, Neto EP, Chaddad-Neto F. Microsurgical Clipping of Low-Riding Basilar Bifurcation Aneurysm. World Neurosurg. 2018 Dec 31. pii: S1878-8750(18)32916-4. doi: 10.1016/j.wneu.2018.12.093. [Epub ahead of print] PubMed PMID: 30605760.
basilar_bifurcation_aneurysm.txt · Last modified: 2019/04/16 21:00 by administrador