A Method for Quantifying Angiographic Severity of Extracranial Vertebral Artery Stenosis

Abstract

Vertebral artery origin stenosis is a common occurrence
among patients with ischemic events in the vertebral and
basilar arterial distribution [1,2]. Of the 407 patients in
the New England Medical Center Posterior Circulation
Registry, 80 (20%) of patients with ischemic events in
the vertebral and basilar arterial distribution had vertebral artery origin occlusion or high-grade stenosis [1].
Treatment options for vertebral artery origin occlusion
or high-grade stenosis associated with ischemic events,
include medical therapy, angioplasty and stent placement, and open surgical revascularization procedures.
Aggressive medical therapy may or may not be effective
for the reduction of cerebral ischemic events among
patients with symptoms caused by hemodynamic
impairment from vertebral artery origin occlusion or
high-grade stenosis [3]. Stent placement is a treatment
option for patients with extracranial vertebral artery
stenosis when patients are having symptoms despite
optimal medical treatment (Class IIb; Level of Evidence
C) [3].
However, no validated or reproducible criteria exist to
quantify the severity of stenosis for effective risk stratification. The Carotid And Vertebral Artery Transluminal
Angioplasty Study (CAVATAS) [4] randomized 16 subjects with vertebral artery origin stenosis (>50% in
severity) to receive either endovascular therapy (angioplasty or stent placement) or medical management
alone. The stenosis severity was calculated from the
images acquired by catheter angiogram using the following formula:
Percent stenosis = 100(1 í A/V)
Where A = diameter of the residual lumen at the point of
maximal stenosis and V = diameter of disease-free distal
vertebral artery. The disease-free segment was defined
at the point where the walls were approximately parallel.
The mean severity of stenosis was 73% (range: 58–92%)
in the endovascular group and 74% (range: 53–95%) in
the medical group.
The reference artery for quantifying the stenosis lies
within the sixth segment which extends classically from
the subclavian artery to the transverse foramen of sixth
cervical vertebrae. The sixth segment of the artery courses obliquely upwards and posteriorly at a distance of 5
to 10 mm from the level of the seventh vertebral body
[5]. Because of severe tortuosity in the sixth segment of
the vertebral artery, seen in approximately 47% of
patients [6], identifying the reference segment on the
basis of parallel alignment of arterial walls may be challenging. To avoid variation in quantification between
observers, we describe another method for identifying
the reference segment of vertebral artery and thus providing a more reliable method for quantifying the
severity of stenosis.