An Acute Ischemic Stroke Classification Instrument That Includes CT or MR Angiography: The Boston Acute Stroke Imaging Scale

F. Torres-Mozqueda; J. He; I.B. Yeh; L.H. Schwamm; M.H. Lev; P.W. Schaefer; R.G. González

doi:10.3174/ajnr.A1000

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Fig 1.
Classification algorithm. Proximal cerebral artery occlusions are depicted in the drawing on the left and are defined as including the following arteries: distal (intracranial) ICA, proximal (M1 or M2) MCA, and/or basilar artery (BA). As shown in the algorithm on the right, the first step was evaluation of CTA or MRA data to identify apparent proximal cerebral artery occlusions. If no proximal cerebral artery occlusion was found, the noncontrast CT or diffusion MR imaging data were reviewed for evidence of a large acute ischemic infarct as defined in the “Materials and Methods” section. If a large CT or DWI abnormality was detected, the patient was classified as having a major stroke. All other circumstances resulted in classification as a minor stroke by imaging.
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Fig 2.
Kaplan-Meier curve of time to discharge. The Kaplan-Meier graph depicts the probability of discharge from hospital in days for patients classified as having major strokes by BASIS and ASPECT (solid line), major by BASIS but minor by ASPECT (dot and dash line), and minor by both classification instruments (dashed line). Overall, a highly significant difference (P < .0001) between the groups was found. In isolating the differences, both the BASIS major/ASPECT major and the BASIS major/ASPECT minor were significantly different from the BASIS and ASPECT minor group (P < .0001). However, there was no significant difference between the BASIS major/ASPECT major (solid line) and the BASIS major/ASPECT minor groups (P = .077).

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Table 1:

Outcomes of 87 patients with ischemic stroke imaged by NCCT and CTA

Variable	Major Stroke by Imaging (n = 43)	Minor Stroke by Imaging (n = 44)	P
Deaths, n	6	0	<.0001
Discharge to rehabilitation facility, n (%)	32 (74)	4 (9)	<.0001
Discharge to home, n (%)	5 (12)	34 (77)	<.0001
Length of stay, days (SE)	12.1 (1.3)	3.7 (0.4)	<.0001

Note:—NCCT indicates noncontrast CT; CTA, CT angiography. Significant differences in outcomes between patients with major and minor stroke were assessed using Fisher exact test (deaths, discharge to a rehabilitation facility, or discharge home) and t test (length of stay). Highly significant differences in all outcome measures were found between patients with major and minor stroke who were initially imaged with NCCT and included CTA. Not included in the table are 11 patients who had NCCT without CTA.

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Table 2:

Outcomes of 118 patients with ischemic stroke imaged by MRI and MRA

Variable	Major Stroke by Imaging (n = 13)	Minor Stroke by Imaging (n = 105)	P
Deaths, n	2	0	<.05
Discharge to rehabilitation facility, n (%)	8 (72)	19 (18)	<.001
Discharge to home, n (%)	3 (27)	84 (80)	<.001
Length of stay, days (SE)	12.9 (3.1)	3.1 (0.2)	<.005

Note:—MRI indicates MR imaging; MRA, MR angiography. Significant differences in all outcome measures were found between patients with major and minor stroke who had MRA as the first angiographic study. Statistical tests for each outcome measure are the same as in Table 1. Not included in this table are 14 patients who had MRI including diffusion MRI but not MRA.

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Table 3:

Outcomes of 87 patients with ischemic stroke imaged by NCCT and CTA and classified by BASIS and ASPECTS

Variable	Major Stroke by BASIS and ASPECTS (n = 22)	Major by BASIS Minor by ASPECTS (n = 21)	Minor Stroke by BASIS and ASPECTS (n = 44)
Deaths, n	5^*	1	0^*
Discharge to rehabilitation facility, n (%)	16 (94)^†^‡	16 (80)^†^‡	4 (9)^†
Discharge to home, n (%)	1 (6)^†^‡	4 (20)^†^‡	34 (77)^†
Length of stay, days (SE)	14.8 (2.4)^§^‖	9.9 (1.1)^§^‖	3.7 (0.4)^§

Note:—NCCT indicates noncontrast CT; CTA, CT angiography; BASIS, Boston Acute Stroke Imaging Scale; ASPECTS, Alberta Stroke Program Early CT Score. There were significant differences in deaths between the BASIS and ASPECTS major stroke group and the minor stroke group classified by BASIS and ASPECTS. Highly significant differences in discharge to rehabilitation and discharge to home were found between the 2 groups that had major stroke classification and the patients classified as minor strokes by BASIS and ASPECTS.
* P < .003.
† All P < .0001.
‡ No significant differences in these outcomes were found between the BASIS and ASPECTS major stroke and BASIS major/ASPECTS minor stroke groups.
§ P < .0001.
‖ Significant differences were found in length of stay between the 2 groups that had major stroke classification and the patients classified as having minor strokes by BASIS and ASPECTS but not between the BASIS and ASPECTS major stroke and BASIS major/ASPECTS minor stroke groups.