====== Posterior circulation intracranial aneurysm ======

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===== Posterior circulation aneurysm classification =====

==== Anatomic Classification ====

Posterior Cerebral Artery (PCA) segments:

P1: Basilar artery tip to posterior communicating artery origin .

P2: Posterior communicating artery to midbrain's dorsal aspect (subdivided into P2A
and P2P) .

P3: Lateral quadrigeminal cistern to calcarine fissure .

P4: Terminal cortical branches .

Alternative S1S3 classification for surgical planning: S1 (interpeduncular/crural
cistern), S2 (ambient/quadrigeminal cistern), S3 (quadrigeminal cistern to cortical
branches) .

Other common sites: Basilar bifurcation (63% of posterior circulation aneurysms), superior
cerebellar artery (SCA), and posterior inferior cerebellar artery (PICA) .

Morphologic and Etiologic Classification
Saccular (berry) aneurysms: Most common (66% of PCA aneurysms), often presenting
with subarachnoid hemorrhage .

Giant serpentine aneurysms: Larger lesions (24% of PCA aneurysms) causing mass effects
(e.g., seizures, hemianopsia) .

Dissecting aneurysms: Often posttraumatic, associated with arterial wall laceration or
stretching against the tentorium .

Fusiform aneurysms: Non-saccular dilations requiring parent vessel occlusion in some
cases .

Pathologic Classification Mizutani System for Basilar Trunk Aneurysms)

1. Acute dissecting

2. Segmental ectasia

3. Mural bleeding ectasia (chronic dissecting)

Posterior circulation aneurysms have a higher rupture risk compared to anterior circulation
aneurysms, particularly when located at the basilar bifurcation or posterior communicating artery

The PHASES score incorporates posterior location as an independent risk factor for rupture



[[Anterior inferior cerebellar artery aneurysm]]

[[Basilar artery aneurysm]] 

[[Posterior cerebral artery aneurysm]]

[[Posterior inferior cerebellar artery aneurysm]]

[[Superior cerebellar artery aneurysm]]

[[Vertebral artery aneurysm]].
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In view of the aggressive natural history of posterior circulation [[traumatic intracranial aneurysm]] (TICA), deSouza et al., recommend that [[CTA]] of the head and neck vessels be performed for cases presenting with post-traumatic disproportionate [[cistern]]al and or [[third ventricle]] or [[fourth ventricle]] SAH. In the event of initial CTA being negative, repeat CTA and if negative [[DSA]] should be performed between 5 to 7 days, with a low threshold for further repeat at 10 days if a traumatic dissection is still suspected. Close monitoring for [[hydrocephalus]] and [[vasospasm]] is required during hospital admission and significant therapy input is likely to be required post discharge from acute care
((deSouza RM, Shah M, Koumellis P, Foroughi M. Subarachnoid haemorrhage
secondary to traumatic intracranial aneurysm of the posterior cerebral
circulation: case series and literature review. Acta Neurochir (Wien). 2016
Sep;158(9):1731-40. doi: 10.1007/s00701-016-2865-6. Epub 2016 Jun 30. Review.
PubMed PMID: 27364895; PubMed Central PMCID: PMC4980416.
)).

[[Intracranial aneurysm]]s (IAs) located in the [[posterior circulation]] are considered to have higher annual bleed rates than those in the [[anterior circulation]]. 

[[Aspect ratio]] and [[parent artery size]] were found to be predictive morphometric factors in differentiating between anterior and posterior cerebral IAs.

Aneurysms of the posterior circulation remain challenging lesions given their proximity to the brainstem and cranial nerves. 

===== Treatment =====

[[Posterior circulation intracranial aneurysm treatment]].