Extracranial Atherosclerosis

KEY FACTS

TERMINOLOGY

• Degenerative process resulting from plasma lipid

deposition in arterial walls

IMAGING

• Smooth/irregular narrowing of proximal ICA

• Ca++ in arterial walls

• ICA, vertebrobasilar arteries most common sites

• Single diameter thresholds for CTA: 2.2 mm (50% stenosis),

1.3 mm (70% stenosis)

• Protocol advice: Color Doppler US as initial screen;

CTA/MRA or contrast MRA; consider DSA before carotid

endarterectomy, in equivocal cases or if CTA/MRA shows

"occlusion"

PATHOLOGY

• NASCET method: % stenosis = (normal lumen - minimal

residual lumen)/normal lumen x 100

• Mild (< 50%), moderate (50-70%), severe (70-99%)

• Intraplaque hemorrhage is independent stroke risk factor

CLINICAL ISSUES

• Carotid endarterectomy (CEA) if symptomatic carotid

stenosis ≥ 70% (NASCET)

• Symptomatic moderate stenosis (50-69%) also benefits

from CEA (NASCET)

• Asymptomatic patients benefit even with stenosis of 60%

(ACAS)

• Carotid stenting depends on preop risk factors

• Signs/symptoms (can be asymptomatic)

○ Carotid bruit, TIA, stroke (may be silent)

DIAGNOSTIC CHECKLIST

• DSA remains gold standard, but acceptable noninvasive

preoperative imaging includes any 2: US, CTA, TOF, or

enhanced MRA

• Late-phase DSA important to rule out pseudocollusion

○ High-grade stenosis with string sign

(Left) Axial CTA shows severe

stenosis of the proximal left

internal carotid artery (ICA)

with small residual lumen ſt.

Peripheral mural calcification

and the lower density lipid-rich

core of the more central soft

plaque in the left ICA are

typical. (Right) Graphic shows

the mild form of ASVD (A)

with "fatty streaks" & slight

intimal thickening. The severe

form (B) is characterized by

intraplaque hemorrhage,

ulceration, & platelet thrombi.

NASCET calculation for % of

stenosis = (b-a)/b x 100, where

b = normal ICA lumen & a =

minimal residual ICA lumen.

(Left) Axial MP-RAGE

sequence shows intraplaque

hemorrhage ﬇ in the right

ICA as a hyperintense crescent.

Intraplaque hemorrhage is an

independent stroke risk factor,

regardless of ICA percent

stenosis. (Courtesy JS McNally,

MD, PhD.) (Right) Coronal

oblique MRA shows signal loss

as a "flow gap" in the left

internal carotid artery ﬇,

indicating severely restricted

flow, typically > 95% stenosis.

The patient underwent an

emergency left carotid

endarterectomy.

Brain: Pathology-Based Diagnoses: Malformations,

Trauma, and Stroke

80