Charles L. Truwit, Nadi Hibri, MD

MD

#{149} A.

James Norman,

#{149} David

Barkovich, MD

MD

#{149} Alisa

Gean-Marton,

MD

of the Insular Ribbon: Another Early CT Sign of Acute Middle Cerebral Artery Infarction’ Loss

Although computed tomography (CT) remains the most frequently used imaging examination in acute cerebral infarction, its sensitivity for early detection of strokes remains limited. In middle cerebral artery (MCA) strokes less than 6 hours old, loss of definition of the gray-white interface in the lateral margins of the insula (“insular ribbon”) was observed. The acute and subacute CT findings in ii retrospective and 16 prospective patients are presented. Loss of the insular ribbon was detected in 12 of the prospective cases and in all 11 retrospective cases. The insular ribbon is supplied by the insular segment of the MCA and its claustral branches. With cessation of MCA flow, the insular ribbon becomes the region most distal from the anterior and posterior cerebral collateral circulations. Consequently, the insular ribbon effectively becomes a watershed arterial zone. Loss of the insular ribbon is thus a reflection of acute edema due to infarction. Loss of the insular ribbon appears to be another frequent and reliable finding in acute MCA stroke.

C

OMPUTED tomography (CT) most frequently employed

is the

subacute

neu-

an 8800 CT scanner

noimaging study in the evaluation of acute cerebral infarction. Unfortunately, despite advances in CT technobogy, the CT scan frequently appears normal within the first hours after infarction, even in the setting of dramatic clinical changes (i). Recentby, Tomura et al (2) reported obscuration of the lentiform nucleus as an early CT finding in middle cerebral artery (MCA) infarction. Several authors have also reported the hyperattenuating MCA as an early sign of infanction, presumably representing acute thrombus within the Ml segment of the MCA (3,4). We report another early CT finding: loss of the gray-white interface at the lateral margin of the insula, which, in our experience, is more frequently observed and more accurate than prior methods for early detection of MCA infarction. We have called this area the insular ribbon, referring to the island of Reil, the extreme capsule, and the cbaustrum. PATIENTS

AND

METHODS

Early

Index terms: Brain, CT, 174.1211 fanction, 174.4352 #{149}Cerebral blood nosis

or obstruction,

Radiology

174.77,

Brain,

#{149}

vessels,

in-

ste-

174.720

postevent non-contrast-enhanced of 1 1 patients with acute MCA infarction were retrospectively reviewed. All patients had clinically suffered major strokes (seven patients) or presented with

CT scans

altered mental CT scans were

1990; 176:801 -806

tic evaluation hemorrhage.

status (four patients); the obtained both for diagnosand to exclude All scans were

significant obtained

9800 CT scanner (GE Medical Milwaukee) except one acute

on a

Systems, and two

tems). formed

From

the

U.S.

Army

Medical

Department,

Academy

of Health

Sciences,

Fort

Sam

Houston,

Tex

(C.L.T.); Neuroradiology Section, Department of Radiology, University of California Medical Centen, San Francisco (C.L.T., A.J.B., D.N.); Neuroradiology Section, Department of Radiology, San Francisco General Hospital, San Francisco (A.G.M.); and Department of Radiology, ropolitan Hospital, San Antonio, Tex (N.H.). Received December 14, 1989; revision ary 15, 1990; revision received April 10; accepted May 1. Address reprint requests

Humana requested to C.L.T.,

MetJanuNeu-

roradiology Section, University of California, Box 0628, 505 Pamnassus Ave. San Francisco, CA 94i43-0628. The opinions expressed herein reflect those of the authors and are not to be construed as reflecting

the C

official

RSNA,

1990

opinion

of the

U.S.

Army

or the

Department

which

were

obtained

(GE Medical

Acute noncontrast within 5 hours

sode on 10 patients.

on

Sys-

CT was perof the clinical epi-

Of these

patients,

four were scanned within 2 hours of their clinical event; two were scanned within 3 hours. Four patients were scanned 3-5 hours after their event. One patient was found unresponsive at home in the morning; her scan was obtained between 41/2 (more likely) and 1 1 ‘/2 hours following her stroke. The acute noncontrast scans

were

obtained

at 10-mm

contiguous

sections.

underwent

follow-up

thickness

with

All patients

but

scanning

one

within

4

days; nine studies were out contrast enhancement, contrast enhancement.

performed withand one with One patient did

not

scanning,

undergo

resolution siveness

MCA

follow-up

of her initial had clinically

distribution

A second collected.

with

dominant

hemiparesis

but

on

state of unresponsuffered a major

stroke.

set of 1 6 cases

tively

The

clinical

prospecpresented

symptoms

(14 patients)

(two patients).

was

patients

Fifteen

of

and

aphasia

patients

were

scanned within 6 hours of their clinical events; the other patient was scanned 810 hours following an intraoperative stroke. Of those patients scanned within 6 hours, two were scanned within 45 mmutes of their clinical event, five were scanned 1 1/221/2 hours after their event, and eight were scanned 31,46 hours after their event. All scans were obtained on a

GE 9800 scanner

at 5-mm

contiguous sections mm thickness and

(seven

thickness

and

(nine patients) on 10contiguous sections

patients.)

Follow-up scans were obtained in 13 of the 16 prospective cases. Nine noncontrast CT scans at 5-mm thickness with contiguous sections (four patients) and 10-mm thickness with contiguous 5cctions

1

scans,

(five

patients)

patient underwent at 5-mm thickness tions. Follow-up

were

(MR) images

were

at 1.5 T (two

cases)

The images knowledge

obtained.

One

contrast-enhanced with contiguous magnetic resonance

obtained and

in three

0.3 T (one

were initially of the clinical

CT 5cc-

cases

case).

read without history. After

of Defense.

Abbreviation:

MCA

middle

cerebral

artery.

801

Table 1 Retrospective

Data

Set Findings Hemi-

Time Course Patient

Data

Insular

Days between

Hours

Patient

Age (y)I Sex

Dominant Clinical Finding

Scans

and2

AMS

2

4

53/M 49/F 68/F 72/F

Hemiparesis Hemiparesis Hemiparesis Hemiparesis

2 2 2 3

1 1 2 3

6

68/M

AMS

3

2

7

64/M

Hemiparesis

4

3

8

40/F

AMS

3.5-5

2

9

58/M

Hemiparesis

4.5

1

io

67/F

Unresponsive

ii

68/F

Hemiparesis -

Anterior

insular

altered

ribbon

I Posterior

spared insular

Posterior

putamen

t Claustrum

status,