Subarachnoid Hemorrhage and Aneurysms Overview

(Left) Diagram depicts the

circle of Willis with relative

prevalence of intracranial

saccular aneurysms (SAs).

Most are "anterior circulation"

with 1/3 occurring on the

ACoA ſt and 1/3 at the

internal carotid/PCoA junction

st; 15-20% are found at the

middle cerebral artery (MCA)

bi- or trifurcation ﬇. 10%

occur on the "posterior

circulation." (Right) Autopsied

Circle of Willis shows a classic

unruptured SA ſt arising from

the junction of the internal

carotid artery ﬇ and the

PCoA st. (Courtesy B. Horten,

MD.)

(Left) Autopsied brain shows a

small ruptured ACoA

aneurysm ﬇ with extensive

focal clot in the

interhemispheric fissure ſt.

Diffuse subarachnoid

hemorrhage is also present.

(Courtesy B. Horten, MD.)

(Right) This patient died of

cerebral ischemia several days

after rupture of a MCA SA ﬇,

which is surrounded by clot in

the sylvian fissure st. Note

the extreme narrowing of the

M1 MCA segment and both

posterior cerebral arteries,

indicative of severe vasospasm

ſt. (Courtesy R. Hewlett, MD.)

(Left) Gross pathology shows

atherosclerotic fusiform

ectasias of the vertebrobasilar

system st, as well as both

internal carotid arteries and

M1 MCA segments ſt. Focal

enlargement of the basilar

artery represents a fusiform

aneurysm ﬇ caused by

atherosclerotic vascular

disease. (Courtesy R. Hewlett,

MD.) (Right)

Nonatherosclerotic fusiform

ectasias of the M1 ſt, A1/A2

﬇, and PCoAs st are seen in

a patient with HIV-associated

vasculopathy. (Courtesy L.

Rourke, MD.)

Trauma, and Stroke

Brain: Pathology-Based Diagnoses: Malformations,

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