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Saccular Aneurysm

KEY FACTS

TERMINOLOGY

• Intracranial saccular aneurysm (SA)

• Outpouching affecting only part of arterial circumference

○ Lacks internal elastic lamina ± tunica media

IMAGING

• Round/lobulated arterial outpouching

○ Usually arises from bifurcations of circle of Willis (COW),

supraclinoid internal carotid and middle cerebral arteries

○ 90% occur in anterior circulation

○ 10% posterior circulation: Basilar tip, cerebellar arteries

(posterior inferior cerebellar artery most common)

○ Rare (< 1%): Trigeminal artery, vertebrobasilar junction

fenestration

• Ruptured SAs result in subarachnoid hemorrhage (SAH)

• May have mural Ca++

• Screening in suspected aneurysmal SAH

○ Multislice CTA sensitivity > 95% for SA > 2 mm

○ 3D TOF: > 90% sensitive for aneurysms ≥ 3 mm

○ DSA still considered "gold standard" but usually

performed only if CTA negative or endovascular

treatment contemplated

TOP DIFFERENTIAL DIAGNOSES

• Vessel loop

• Vessel infundibulum

CLINICAL ISSUES

• Vast majority of unruptured SAs are asymptomatic

○ 2-6% incidental finding at autopsy, imaging

• 80-90% of nontraumatic SAH caused by ruptured SA

• Treatment

○ Endovascular coiling vs. surgical clipping still

controversial

○ 22.6% relative, 6.9% absolute risk ↓ for coiling vs.

surgery for ruptured aneurysms

○ ↓ morbidity, mortality, and hospital costs; quicker

recovery for unruptured aneurysms

(Left) Most common sites for

saccular aneurysms (SAs) are

anterior communicating artery

(ACoA) ſt and IC-PC junction

﬇. Middle cerebral artery

(MCA) bifurcation st and

basilar tip ﬈ are other

frequent sites. (Right) Graphic

illustrates rupture of an ACoA

aneurysm ﬇ with active

extravasation from a

superiorly directed bleb

(Murphy teat). An additional

posterior communicating

artery SA st and tiny bleb at

the left MCA bifurcation ſt

are seen. Patients with SAs

have a 20% chance of having >

1 aneurysm.

(Left) A 63-year-old man was

found down in a parking lot

and brought to the ER. Axial

NECT scan showed diffuse

subarachnoid hemorrhage ſt

with a focal hematoma ﬇ in

the anteroinferior aspect of

the interhemispheric fissure.

(Right) Coronal MIP of the CTA

in the same patient shows a 4-

mm SA ſt projecting upward

from the ACoA.

Trauma, and Stroke

Brain: Pathology-Based Diagnoses: Malformations,

113