Correlation of Neurologic Dysfunction with CT Findings in Early Acute Stroke

Abstract

To determine the frequency of early computed tomographic (CT) findings of ischemia and their relationship to symptom duration and neurologic dysfunction within 3 hours of ischemic stroke.
The CT scans of 39 acute stroke patients were evaluated for signs of early ischemic change within 3 hours of symptom onset and without knowledge of the patient's neurologic deficit or results of a 24 hour follow-up post-thrombolysis CT. Early CT signs of acute ischemic change or thromboembolism were hypoattenuation of the insular ribbon, obscuration of the lentiform nucleus, cortical hypodensity/effacement, and hyperdense middle cerebral artery sign.
Signs of acute ischemic change were seen on the baseline scan in 25/39 patients (64%). Hypoattenuation of the insular ribbon was seen in 11 patients, obscuration of the lentiform nucleus in 13, cortical hypodensity/effacement in 13, and hyperdense middle cerebral artery sign in 7. The prevalence of early ischemic signs was directly associated with increasing neurologic disability at the time of presentation. No clear relationship existed between symptom duration and the presence of CT signs.
Evidence of cerebral ischemia is frequently seen on CT within 3 hours of symptom onset. The degree of neurologic disability correlates with CT signs of ischemia.

Full text

Correlation of Neurologic Dysfunction
with CT Findings in Early Acute Stroke
J.N. Scott, A.M. Buchan and
R.J.
Sevick
ABSTRACT: Objective: To determine the frequency of early computed tomographic (CT) findings of
ischemia and their relationship to symptom duration and neurologic dysfunction within 3 hours of
ischemic stroke. Methods: The CT scans of 39 acute stroke patients were evaluated for signs of early
ischemic change within 3 hours of symptom onset and without knowledge of the patient's neurologic
deficit or results of a 24 hour follow-up post-thrombolysis CT. Early CT signs of acute ischemic change
or thromboembolism were hypoattenuation of the insular ribbon, obscuration of the lentiform nucleus,
cortical hypodensity/effacement, and hyperdense middle cerebral artery sign. Results: Signs of acute
ischemic change were seen on the baseline scan in 25/39 patients (64%). Hypoattenuation of the insular
ribbon was seen in 11 patients, obscuration of the lentiform nucleus in 13, cortical hypodensity/efface-
ment in 13, and hyperdense middle cerebral artery sign in 7. The prevalence of early ischemic signs was
directly associated with increasing neurologic disability at the time of presentation. No clear relationship
existed between symptom duration and the presence of CT signs. Conclusions: Evidence of cerebral
ischemia is frequently seen on CT within 3 hours of symptom onset. The degree of neurologic disabili-
ty correlates with CT signs of ischemia.
RESUME: Correlation entre la dysfonction neurologique et les observations au CT scan dans l'accident vas-
culaire cerebral en phase precoce.
Objectif:
II
s'agit
de determiner la frequence de manifestations precoces d'is-
chemie a la tomographie assistee par ordinateur (CT) et leur relation avec la duree de la symptomatologie et avec la
dysfonction neurologique, en dedans de trois heures d'un accident vasculaire cerebral ischemique (AVCI). Methodes:
Nous avons examine le CT scan de 39 patients presentant un AVCI pour d&ecter des signes precoces de changements
ischemiques en dedans de 3 heures du debut des symptomes et sans connattre le deficit neurologique du patient ou les
resultats du CT fait 24 heures apres la thrombolyse. Les signes precoces de changements ischemiques aigus au CT ou
de thrombo-embolie etaient une hypoattenuation du ruban insulaire, une obscuration du noyau lenticulaire, une hypo-
densite/un effacement cortical et le signe de I'artere cerebrate moyenne hyperdense.
Resultats:
Des signes de change-
ments ischemiques aigus ont ete observes au scan initial chez 25 patients sur 39 (64%). Une hypoattenuation du ruban
insulaire a ete observee chez 11 patients, une obscuration du noyau lenticulaire chez 13, une hypodentite/un efface-
ment cortical chez 13 et le signe de I'artere cerebrale moyenne hyperdense chez 7. La prevalence de signes
ischemiques precoces etait directement associee a un deficit neurologique progressif au moment ou le patient a con-
suite.
II n'existait pas de relation claire entre la duree des symptomes et la presence de signes au CT
scan.
Conclusions:
Des manifestations d'ischdmie cerebrale sont observees frequemment au CT scan en dedans de 3 heures du debut des
symptomes. Le degre de dysfonction neurologique est en correlation avec les signes d'ischemie observes au CT scan.
Can. J. Neurol. Sci. 1999; 26: 182-189
The primary role of CT scanning in patients with sudden
onset of neurologic symptoms has been the detection of intracra-
nial hemorrhage and to exclude disease processes that may
mimic ischemia (e.g., tumor or subdural hematoma). However,
the increasing use of thrombolytic therapy as treatment for acute
stroke necessitates that stroke team members also recognize
often subtle changes on CT scan which may represent early
ischemic change.
Signs of acute cerebral ischemia or thromboembolism have
been described by others and include hypoattenuation of the
insular ribbon,1 obscuration of the lentiform nucleus,2 cortical
hypodensity/effacement of other hemispheric territories,13 and
the hyperdense middle cerebral artery (MCA) sign.4"6
The presence of CT signs of hemispheric brain ischemia may
increase the risk of deterioration, with or without cerebral hem-
orrhage, after thrombolytic therapy. As such, clinical studies
which have examined the benefit of thrombolytic therapy for
stroke have emphasized that a short time from the ischemic event
From the Departments of Diagnostic imaging (J.N.S., R.J.S.). Clinical Neurosciences
(A.M.B.,
R.J.S.), and Anatomy (R.J.S.), Foothills Hospital, University of Calgary and
the Alberta Stroke Program, Calgary, Alberta, Canada. R.J.S. is a member of the
Seaman Family MR Research Centre.
RECEIVED OCTOBER 22, 1998. ACCEPTED IN FINAL FORM MARCH 18, 1999.
Reprint requests to: Dr. R.J. Sevick, Department of Diagnostic Imaging, Foothills
Hospital, 1331 - 29 Street N.W., Calgary, Alberta, Canada T2N 4N2
182

LE JOURNAL CANADIEN DES SCIENCES NEUROLOGIQUES
to treatment and the absence of any sign of brain injury on CT
are important inclusion criteria.7,8
This clinical and radiological study was prompted after
reviewing the CT scans of patients treated with recombinant
tis-
sue plasminogen activator (rt-PA) at our stroke center in which
we found a higher frequency of acute ischemic signs than was
originally expected. Our study is a practical extension of the
application of rt-PA in acute ischemic stroke presenting within 3
hours of symptom onset, and evaluates the prevalence and distri-
bution of early ischemic signs in a large patient population. The
results of this analysis may aid members of the stroke team in
developing acute management strategies.
MATERIALS AND METHODS
Our regional stroke program serves a population of approxi-
mately 1.5 million. Patients who present at our institution early
after suspected stroke are referred urgently to the acute stroke
treatment team. Patients are evaluated by the stroke neurologist,
and CT scan and appropriate laboratory studies are obtained
before the patient is transferred to the acute stroke unit where a
final decision regarding thrombolytic therapy is made. Patients
are entered into an acute stroke database and all imaging studies
are archived.
We reviewed the CT scans and medical records of 39 consec-
utive prospectively gathered patients between April 1, 1996 and
December 21, 1997 who presented within 3 hours of onset of an
acute ischemic neurologic deficit and were treated with intra-
venous rt-PA. The patients were required to have had an
ischemic stroke with a clearly defined time of onset, a deficit
measurable using the National Institute of Health Stroke Scale
(NIHSS), and a baseline CT scan of the brain that showed no
evidence of intracranial hemorrhage.
The patients had a neurological examination and were scored
using the NIHSS immediately before rt-PA treatment. The
NIHSS score is 0 for a healthy patient and 42 for a comatose
patient with all scale items maximally impaired. Patients with
minimal symptoms, rapidly improving clinical deficits, evidence
of evolving infarction involving more than one-third of the com-
promised vascular territory, or other previously described exclu-
sion criteria7 were not considered candidates for thrombolytic
therapy and were therefore not included in this study.
All patients had at least two CT scans, the first within 3 hours
of symptom onset and the second CT approximately 24 hours
post-acute management. All baseline CT scans were reviewed by
two of the authors without knowledge of the patients' clinical
symptoms or their time of onset, or of any findings on the subse-
quent CT studies. In cases where the baseline scan was felt to be
normal, the 24-hour study was then assessed for regions of acute
ischemia which, in retrospect, could also be seen as abnormal on
the initial study.
CT scans of the brain without intravenous contrast were per-
formed on most patients using a Toshiba Xpress SX helical scan-
ner with the remaining studies performed using a General
Electric HiSpeed Advantage scanner. Images were acquired
using contiguous axial 6-mm sections from the foramen magnum
to the suprasellar region and 10-mm contiguous slices through
the remainder of the brain.
Signs of acute ischemic change, and the parent vessel territo-
ry of the ischemic region were documented as follows.
Hypoattenuation of the insular ribbon was defined as loss of
dif-
ferential density between subcortical white and gray matter of
the insular cortex. Obscuration of the lentiform nucleus was
defined as a decrease in density involving the lentiform nucleus
and loss of gray-white matter differentiation in this area. Cortical
hypodensity/effacement was defined as an area of hypodensity
within a cortical region other than the insula, or subtle mass
effect with effacement of cortical sulci. Hyperdense MCA sign
was defined as hyperdensity within the MCA that was greater
than the contralateral MCA or any other intracranial vessel of
similar size not attributable to calcification.
The data were expressed as mean ± standard error of the mean
(S.E.M.) and analyzed with either a two-sample (unpaired) t-test
or non-parametric test for comparison of two means (Mann-
Whitney Two Sample Test).
RESULTS
A total of 39 patients were evaluated and 78 CT scans were
reviewed. There were 24 male and 15 female patients with a mean
age of
68.3
± 2.2 years (range, 24 to 95). At admission, all patients
presented with severe hemispheric symptoms that scored between
4 and 24 points (mean, 13.8 ± ( 0.85) on the NIHSS. As an exam-
ple,
a typical patient with an NIHSS score of 9 and right MCA
occlusion might exhibit a complete left hemianopia, minor left
facial paresis, left hemiparesis with minimal effort against gravity
of both arm and leg, partial sensory loss, and mild dysarthria.
CT Characteristics
The baseline CT was performed at a mean time of 112 ± 5
mins (range, 53 to 160 mins) from symptom onset. The baseline
CT scan was normal in 36% of the patients and showed at least
one abnormality in 64% (Table 1). The second CT was per-
formed approximately 24 hours post-thrombolytic therapy and
was abnormal in 85% of patients. All patients who had an early
Table 1: Summary of Clinical Characteristics and Computed Tomographic Scan Results in 39 Patients.
Radiographic Features Baseline CT scan
»(%) 24 Hour Follow-up CT Scan
n(%)
Hypoattenuation of the insular ribbon
Obscuration of the lentiform nucleus
Cortical hypodensity/effacement
Hyperdense MCA sign
No acute findings
Hemorrhage1
11
13
13
7
14
0
(28%)
(33%)
(33%)
(18%)
(36%)
(0%)
11
16
16
2
6
12
(28%)
(41%)
(41%)
(5%)
(15%)
(31%)
'Varies from petechial hemorrhage to lobar hematomas.
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THE CANADIAN JOURNAL OF NEUROLOGICAL SCIENCES
Figure 1:
Hypoattenuation
of
the
insular
ribbon,
(a)
Hypodensity
of
the
insular cortex with
resultant
decreased density of
the
affected gray matter
(arrows).
Note is also made of
the
low density of
the
adjacent
temporal
opercular
cortex,
(b) 24-hour follow-up CT
scan
shows large
MCA
territory
infarction
with
hyperdense
clot
visible
in Sylvian
branches
of the MCA.
Figure 2:
Obscuration
of the
lentiform
nucleus,
(a)
Subtle decrease
in density of the
lentiform nucleus
on the
right (arrows) compared
with its
normal
counterpart
on the
left,
(b)
Follow-up
scan 24 hours later
shows infarct localized
to
putamen
and posterior limb of the
internal
capsule.
ischemic sign on their baseline scan had a corresponding positive
sign on their follow-up study.
Early Ischemic Signs
The CT findings at varying intervals after the onset of symp-
toms are shown in Table 1 and in Figures 1 to 4. On the baseline
CT scan, hypoattenuation of the insular ribbon was identified in
11/39 (28%) of patients, obscuration of the lentiform nucleus in
13 (33%), cortical hypodensity/effacement in 13 (33%), and
hyperdense MCA sign in 7 (18%). In five patients, subtle signs
of acute ischemic change (hypoattenuation of the insular ribbon,
2;
obscuration of the lentiform nucleus, 1; cortical hypodensi-
ty/effacement, 3) were seen retrospectively on the baseline CT
after viewing the follow-up study. No early findings were noted
on the baseline CT in 14 (36%) patients. In addition to signs of
early ischemic change, seven patients had evidence of old infarc-
tion on their baseline CT studies.
On the follow-up CT scan only six (15%) studies were normal
and detection of infarction was increased with hypoattenuation
of the insular ribbon identified in 11/39 (28%) of patients, obscu-
ration of the lentiform nucleus in 16 (41%), and cortical hypo-
density/effacement in 16 (41%). The hyperdense MCA sign was
184

LE JOURNAL CANADIEN DES SCIENCES NEUROLOGIQUES
Figure
3:
Cortical hypodensity/effacement
in
the ACA
territory,
(a)
Decreased density
of
the affected cortical
gray
matter in
the
left
medial frontal lobe
(arrows).
Incidental chronic
right frontal
infarct,
(b) 24-hour follow-up
CT scan shows
small
acute
left frontal
infarct.
Figure 4:
Hyperdense MCA
sign,
(a)
Hyperdense
clot is
shown
in the Ml
segment
of the
MCA
(arrow),
(b) 24-hour follow-up
CT scan
shows
massive
MCA
territory
infarction,
the
artery
no
longer appears
hyperdense.
identified in 2 (5%) patients (Table 1). In the 33 cases with pos-
itive ischemic changes, the infarcts involved the MCA vascular
territory in 29 patients, the anterior cerebral artery (ACA) in two,
and the posterior cerebral artery (PCA) in two. Secondary bleed-
ing was present in 12/39 (31%) cases and always occurred either
within the infarction itself or the region corresponding to the
presenting symptoms if the baseline study was normal. Every
patient who had an early sign of infarction on their baseline CT
had a corresponding infarction on the follow-up study except for
three patients who had lobar hemorrhages.
Time of Initial CT and Early Ischemic Signs
The earliest CT scan that showed parenchymal hypoattenua-
tion of any degree was obtained 53 minutes after the onset of
symptoms. There was no significant difference in the initial clin-
ical severity between patients with early (< 90 mins; NIHSS 15.3
± 1.86, n = 9) and later (90-180 mins; NIHSS 13.3 ± 0.95, n =
Volume 26, No. 3 - August 1999 185

THE CANADIAN JOURNAL OF NEUROLOGICAL SCIENCES
Table 2: Correlation of Computed Tomographic Scan Results with Symptom Duration in 39 Patients.
Symptom Duration Insular1 Lentiform2 Cortex3 MCA clot4 No Acute Findings
0 - 90 mins (n = 9)
Mean 65 ± 3.8 mins (range, 53-76)
90-
180 mins (n = 30)
Mean 127 ± 3.1 mins (range, 94-160)
4 (44%)
7 (23%)
2 (22%)
11 (37%)
4 (44%)
9 (30%)
3 (33%)
4 (13%)
3 (33%)
11 (37%)
'Insular, hypoattenuation of the insular ribbon (see Materials and Methods)
2Lentiform, obscuration of the lentiform nucleus
3Cortex, cortical hypodensity/effacement
4MCA clot, hyperdense middle cerebral artery sign.
30) CT studies (P - 0.3275). The relative number of patients with
normal CT studies was similar between the 0-90 min and 90-180
minute groups (Table 2). There was no clear association between
the time at which the baseline CT was performed and signs indi-
cating acute infarction or thromboembolism. A slightly greater
proportion of patients who had their baseline CT scan within 90
minutes of symptom onset had hypoattenuation of the lentiform
nucleus, cortical hypodensity/effacement, and a hyperdense
MCA sign, whereas the most common finding between 90-180
minutes was obscuration of the lentiform nucleus.
Severity of Neurologic Dysfunction and Early Ischemic Signs
An increasing frequency of acute ischemic signs was associ-
ated with an increasing severity of neurological deficit at patient
presentation (Figure 5). The NIHSS scores for patients with nor-
mal CT scans (mean, 10.1 ± 1.54) were significantly lower than
those for patients whose scans showed any ischemic finding
(mean, 15.9 ± 0.08) (P = 0.0012) (Figure 5A); or hypoattenua-
tion of the lentiform nucleus (mean, 16.2 ± 1.41) (P = 0.0092),
obscuration of the lentiform nucleus (mean, 16.1 ± 1.14) (P =
0.0049), cortical hypodensity/effacement (mean, 15.9 ± 1.25) (P
= 0.0074) (Figure 5B); or the hyperdense MCA sign (mean, 18.3
± 1.54) (P = 0.0034) (Figure 5B).
Furthermore, for patients with a NIHSS of 1 to 10, no acute
ischemic signs were detected in 9/10 (90%) cases (Table 3). A
single patient had hypoattenuation of the insular ribbon, obscu-
ration of the lentiform nucleus and cortical hypodensity/efface-
ment. In contrast, only 3/17 (18%) patients with an NIHSS of 11
to 16, and 2/12 (17%) with an NIHSS of 17 to 24 had normal CT
scans.
261
24-
22-
20-
18-
16-
co
CO
14-
*12-
10-
8-
6-
4-
2-
QJ
A
•
D
•
DD
• •
DD
•
DD
DD
Normal
•
•
•
•
• ••
• ••
• •••
• ••
•
• ••
• •
•
Acute Ischemic
Sign
B
•
•
•
• •
• •
• •
•
•
Insular
•
•
• •
• •
• •
•
•
• •
•
Lentiform
•
•
• •
•
• •
• *
•
•
•
•
Cortex
•
•
•
•
•
•
•
MCA Clot
Figure 5:
Correlation
of NIHSS with CT
scan
results in 39
patients.
(A)
Comparison between
normal and
positive
CT
scans
with any sign of acute
ischemia
or
thromboembolism,
and
(B) with
the
individual
signs.
Insular,
hypoattenuation
of the
insular
ribbon;
Lentiform,
obscuration
of the
lentiform
nucleus;
Cortex,
cortical
hypodensity/effacement;
MCA
clot,
hyperdense MCA
sign.
186

Table 3: Correlation of
NIHSS
1
with Computed Tomographic Scan Results in 39 Patients.
NIHSS Insular2 Lentiform3 Cortex4 MCA clot5 No Acute Findings
0- 10(n=10)
Mean 6.8 ±0.71 1 (10%) 0 (0%) 1 (10%) 1 (10%) 9 (90%)
11 -
16
(n= 17)
Mean 13.8 ±0.46 5 (29%) 3 (18%) 6 (35%) 7 (41%) 3 (18%)
17-24(n= 12)
Mean 19.6 ±0.74 5 (42%) 4 (33%) 6 (50%) 5 (42%) 2 (17%)
'NIHSS,
National Institutes of Health Stroke Scale (see Materials and Methods)
2Insular, hypoattenuation of the insular ribbon
3Lentiform, obscuration of the lentiform nucleus
4Cortex, cortical hypodensity/effacement
5MCA clot, hyperdense middle cerebral artery sign
DISCUSSION
It has been previously reported that detection of ischemic
changes on CT images within 6 hours of a stroke is poor.9"10 In
fact, until recently, the general consensus has been to use CT
scans following infarction to exclude hemorrhage, subdural
hematoma, or mass rather than the demonstration of infarction.
The earliest CT scanners initially gave the impression that infarc-
tion could not be seen prior to 24 hours after symptom onset,"'2
although an increasing number of reports have now described
detection of several well defined signs of acute ischemic
change.1'61314 We set out to confirm our impression that CT
signs which indicate acute ischemia can be found much earlier
and in a higher percentage of patients with acute stroke than was
originally believed.
Early CT abnormalities were found in the majority of our
patients (64%) within 3 hours of symptom onset, which is simi-
lar to previous reports that vary from 40 to
80%1,2'15
depending
upon the time that the CT scan was performed. In our series, indi-
vidual signs of acute ischemic change were evident in 67% of
patients whose baseline CT was performed within 90 minutes of
symptom onset. Selection of patients from the literature who
were scanned within the same time period yields a similar rate of
detection between 38 and
75%.',2,15
However, it is important to
note that many additional patients within our study period were
excluded from analysis because their ischemic changes were
deemed too extensive for them to receive rt-PA. Therefore, our
data likely underestimate the true frequency of early CT signs of
ischemia within a general stroke population.
The importance of recognizing findings of early ischemia on
CT scans is paramount for several reasons. The recognition of
parenchymal hypodensity and/or effacement of sulci in more
than one-third of the MCA territory is often used as an exclusion
criteria for patients receiving intravenous thrombolytic thera-
py.815 In addition to increasing age and severity of clinical
deficit,16 the risk of hemorrhagic transformation of the infarct
following recanalization and reperfusion post-thrombolysis is
thought to increase with enlarging size of the ischemic lesion on
CT.17
Finally, assessment of early ischemic CT signs has been
reported to help predict clinical response to thrombolytic thera-
py, with patients having smaller ischemic regions benefiting to a
greater extent.15'18
Hypoattenuation of the insular ribbon, or decreased density of
the affected gray matter at the lateral margin of the insula, was
initially described by Truwit1 as the most frequently observed
LE JOURNAL CANADIEN DES SCIENCES NEUROLOGIQUES
sign of acute ischemia within the MCA territory. The blood sup-
ply to the insular region is provided mainly by the insular seg-
ment of the MCA and its claustral branches. In MCA occlusion
distal to the lenticulostriate arteries, the insular ribbon becomes
the region furthest from potential collateral flow from the anteri-
or and posterior cerebral circulation and so it effectively
becomes a watershed zone. In our series, hypoattenuation of the
insular ribbon was frequently seen early after the onset of
ischemia, even before 90 minutes, although its overall frequency
was similar to other signs.
Obscuration of the lentiform nucleus has been described as a
common sign of acute infarction, often being recognized as early
as one hour after symptom onset.2 This deep MCA territory is
also extremely sensitive to ischemia and is likely because the
lenticulostriate arteries which supply it are end-arteries with no
potential for collateral blood flow. In our series, obscuration of
the lentiform nucleus was the most common sign overall and its
presence correlated well with subsequent deep MCA infarction
(positive predictive value 100% and negative predictive value
88%).
Hemispheric cortical hypoattenuation (other than insular cor-
tex) and sulcal effacement occurred together in almost all cases
in our series. Cortical hypodensity/effacement was found in 33%
of our patients which is similar to previous reports that vary from
33 to 46% within 3 hours of symptom onset.1,2 However, in the
present study and others,12'13 cortical hypoattenuation/efface-
ment is a relatively infrequent early ischemic sign in isolation (0
to 17%) which likely reflects, in part, the greater proportion of
MCA versus non-MCA territory strokes. In our series, only 5/39
(13%) patients had an isolated cortical hypodensity/effacement
sign; four of which were within either the ACA or PCA vascular
territories.
The hyperdense MCA sign is an indirect sign of ischemia cor-
responding to arterial occlusion that may be visualized on early
noncontrast CT scans before an infarct becomes evident. While
increased attenuation may in fact represent a thrombus within the
MCA, adult patients occasionally manifest atherosclerotic calci-
fications that can simulate an acute thrombus,1 suggesting that
the hyperdense MCA sign may not be a reliable indicator of ves-
sel occlusion.19 The strict definition we used required that the
hyperdensity within the MCA be greater than the contralateral
MCA, or any other intracranial vessel of similar size not attrib-
utable to calcification, to be considered positive13'20 and likely
reflects a more accurate incidence in the setting of acute stroke.
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THE CANADIAN JOURNAL OF NEUROLOGICAL SCIENCES
Hyperdense MCA sign was present in only seven (18%) of our
patients while previous studies have described higher incidences,
varying between 33 to
47%.''
2
'"
23
However, several of these
reports' have excluded non-MCA territory strokes which
could artifactually elevate its frequency when comparing to a
general stroke population. The lysis of clot, due to endogenous
thrombolytics, is a natural phenomenon which thrombolytic
therapy is seeking to accelerate and this would account for only
two of the hyperdense MCA signs persisting on the follow-up
studies.22'24'25
Our results show a clear association between the number of
early CT ischemic signs and initial clinical severity.7.8,i3.i5,2i,26
Increasing neurologic disability, as measured using the NIHSS,
correlated closely with the presence of CT signs of ischemia in
the setting of acute stroke. Furthermore, 90% of patients with a
low NIHSS (0-10) had negative CT studies compared to only
17%
in the more disabled groups. This relationship most likely
reflects the individual's available collateral circulation,27 with
those patients who have fewer collaterals experiencing more
severe ischemia and developing increased neurologic impair-
ment and early CT changes. In contrast, no significant relation-
ship between symptom duration and the presence of ischemic
signs in the acute setting was evident," with similar percentages
of patients having negative CT studies in each of the two time
periods examined.
Hemorrhagic transformation, symptomatic and asympto-
matic, was observed in 12 of the 39 patients (31%) on the 24-
hour follow-up CT scans. This frequency is similar to previous
reports of acute stroke patients treated with rt-PA.7'8'28
Hemorrhagic transformation is a common accompaniment of
embolic infarction even in patients not treated with thrombolyt-
ics and appears related to both the intensity of ischemia and
delayed infarct extension, but not with the presence of early CT
signs of ischemia.I3,22'28 Previous natural history studies have
reported similar incidences of hemorrhagic transformation, vary-
ing between
33-43%
in acute stroke patients evaluated by either
serial CT1317'29 or autopsy studies.30 More recently, the detection
of deoxyhemoglobin by gradient echo magnetic resonance
sequences, or methemoglobin on Tl-weighted sequences pro-
vides an exquisite look at trace amounts of blood and illustrates
that petechial hemorrhagic transformation is more frequent than
CT studies suggest.31'32 Different variables, including the use of
anticoagulants, embolic versus atherosclerotic stroke, and time
elapsed from stroke onset have all been postulated to increase the
risk of hemorrhagic transformation in stroke patients.
This study was a retrospective review of a group of stroke
patients and the reviewers were aware that the patients were sub-
sequently treated with thrombolytic therapy. Scan interpretation
by stroke team members in a prospective manner may yield a
lower rate of detecting acute ischemic changes. However, clini-
cal information about the site of cerebral ischemia would
improve the observer's detection of CT signs. Knowledge of the
follow-up scans led to subtle signs being detected in five addi-
tional patients and would not have altered treatment decisions.
In conclusion, the early diagnosis of ischemic infarction by CT
depends on recognition of often subtle changes of reduced attenua-
tion and slight mass effect. It is only through gaining further knowl-
edge of the particular early CT changes, in collaboration with other
studies that correlate long-term outcome with or without use of
thrombolytics, that we can make informed initial decisions regard-
ing use of thrombolysis for the individual patient. The present study
reinforces that early ischemic changes are frequently present with-
in the first few hours of cerebral infarction and, as a result, the CT
scan is now more carefully examined at our center. The presence of
early ischemic signs correlated more closely with the severity of the
patient's neurologic dysfunction than the length of time from symp-
tom onset in the acute setting. Recognition of early CT signs of
ischemia should aid members of the stroke team in developing
acute management strategies for their patients.
ABBREVIATIONS
CT,
computed tomography, MCA, middle cerebral artery,
NIHSS,
National Institute of Health Stroke Scale; rt-PA, recom-
binant tissue plasminogen activator.
ACKNOWLEDGEMENTS
We thank our patients and their families for participating in this
study, and Peggy Kochanski and Marilyn Mora for their expert assis-
tance. This study was supported in part by the Heart and Stroke
Foundation of Alberta and an infrastructural grant from the Alberta
Stroke Program.
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