1. ings in our study should therefore be compared with those in
forthcoming studies on both techniques conducted at several
centers.
References
1. Rociu E, Stoker J, Eijkemans MJ, Schouten WR, Lameris JS. Fecal
´
incontinence: endoanal US versus endoanal MR imaging. Radiol-
ogy 1999; 212:453– 458.
2. Briel JW, Stoker J, Rociu E, Lameris JS, Hop WCJ, Schouten WR.
´
External anal sphincter atrophy on endoanal magnetic resonance
imaging adversely affects continence after sphincteroplasty. Br J
Surg 1999; 86:1322–1327.
Jaap Stoker, MD, PhD, Elena Rociu, MD, PhD, and Johan S.
Lameris, MD, PhD
´
Department of Radiology, Academic Medical Center, According to Dr Lev and colleagues (1), “the infarct is barely detect-
University of Amsterdam able as a minimum area of hypoattenuation of the left caudate head”
Meibergdreef 9, 1105 AZ Amsterdam, the Netherlands (large arrow), although the entire MCA territory is hypoattenuating
e-mail: j.stoker@amc.uva.nl (small arrows), in contrast with the unaffected right hemisphere, on
these transverse CT scans.
Acute Stroke: How to Improve CT Detection and
Avoid Errors in Radiology of an erroneous CT reading; figure 2a shows two nonen-
hanced CT sections obtained 1.5 hours after left MCA stroke.
Even in this reproduction of the CT scans (Figure), gray and
From: white matter can be differentiated in the right hemisphere.
Rudiger von Kummer, MD
¨ The sulci and the upper insular cistern are nicely surrounded
Department of Neuroradiology, University of Technology by the hyperattenuating cortex, and the upper part of the
Fetscherstrasse 74, D-01307 Dresden, Germany putamen can be distinguished from the internal and external
e-mail: kummer-r@rcs.urz.tu-dresden.de capsules. The typical cortical attenuation is also present in
the left occipital lobe and portions of the left frontal lobe.
The remaining portion of the left hemisphere is, however,
Editor:
completely hypoattenuating and corresponds to the territory
I read with great interest the suggestions of Dr Lev and
of the left MCA with a sharp temporo-occipital margin lateral
colleagues in the October 1999 issue of Radiology (1) on
to the left trigonum (small arrows, Figure). In this area, gray
improving the detection of early ischemic brain edema by
varying the window width and center level and in the July and white matter cannot be distinguished. The left basal
1999 issue of Lancet (2) on avoiding errors in radiology. I fully ganglia are obscured. I do not see the insular or temporal
agree that errors in the interpretation of radiographic studies cortex. This is, in my experience (6), the typical finding of a
can be attributed to perceptual misses, poor judgment, in- total MCA infarction clearly exceeding one-third of the MCA
complete knowledge, or poor technique in obtaining and territory.
reviewing radiographs (3). I wonder which of these reasons I do not agree with the opinion of Dr Lev and colleagues
make the interpretation of computed tomographic (CT) scans that “the infarct is barely detectable as a minimal area of
after acute stroke so problematic. hypoattenuation of the left caudate head.” I wonder why this
In a recent article by Grotta et al (4), 16 experts involved in extended ischemic edema was missed by such an experienced
the National Institute of Neurological Disorders and Stroke group of radiologists and the reviewers of this distinguished
rt-PA [recombinant tissue-type plasminogen activator] Stroke journal. I wonder how many subscribers to Radiology would
Study found that CT was much less sensitive (78%) and miss such an important finding. And what are the reasons for
specific (57%) in depicting any early changes or in helping to such errors? I do not think that the CT technique is the
identify changes involving more than 33% of the middle problem in this case. From my perception, I can more easily
cerebral artery (MCA) territory in a comparison with findings detect and outline the entire area of hypoattenuation in
made by the group’s neuroradiologist. Investigators in the figure 2a than in figure 2b (1), which shows the same scan
first European Cooperative Acute Stroke Study (ECASS) (5) with reduced window width and increased center level. I
used double readings to detect protocol violators and found presume that the obscuration of anatomic structures by the
52 patients with major early infarct signs not identified by ischemic edema causes perceptual misses. I also presume that
the local investigators. Fifty-two is, however, less than half of the knowledge about the cause of hypoattenuation on CT
all 109 protocol violations, in contrast to what was said by Dr scans in patients with early ischemic stroke is incomplete.
Lev and colleagues (1). With this CT scan interpretation, the values for the sensitiv-
This article (1)—although the sensitivity of CT in acute ity and the specificity of CT presented by Dr Lev and col-
stroke is the topic—involuntarily provides another example leagues do not impress me.
920 Radiology September 2000

2. References hypoattenuation that is relevant. Because an ischemic area
1. Lev MH, Farkas J, Gemmete JJ, et al. Acute stroke: improved of hypoattenuation was seen to be present in both figure 2a
nonenhanced CT detection— benefits of soft-copy interpretation and 2b, our interpretation was that stroke was present on
by using variable window width and center level settings. Radi-
ology 1999; 213:150 –155. both images (albeit more conspicuously seen in fig 2b). In
2. Lev MH, Rhea JT, Bramson RT. Avoidance of variability and error fact, this case did not contribute to the reported differences
in radiology. Lancet 1999; 354:272. in sensitivity and specificity between the standard and the
3. Berlin L. Malpractice issues in radiology: perceptual errors. AJR nonstandard review settings. In only three of the 21 (14%)
Am J Roentgenol 1996; 167:587–590.
4. Grotta JC, Chiu D, Lu M, et al. Agreement and variability in the cases reviewed did the use of nonstandard review settings
interpretation of early CT changes in stroke patients qualifying result in a change of category from negative to positive for
for intravenous rtPA therapy. Stroke 1999; 30:1528 –1533. stroke. As noted in our article, because the cases we re-
5. Hacke W, Kaste M, Fieschi C, et al. Intravenous thrombolysis with viewed were intentionally selected to be challenging, the
recombinant tissue plasminogen activator for acute hemispheric
stroke: the European Cooperative Acute Stroke Study. JAMA
sensitivity and specificity values we reported were not in-
1995; 274:1017–1025. tended to reflect those that would be obtained from a truly
6. von Kummer R, Bozzao L, Manelfe C. Early CT diagnosis of random population. Nevertheless, even a small improve-
hemispheric brain infarction. Heidelberg, Germany: Springer, ment in the accuracy of CT stroke detection could be
1995.
clinically important.
We apologize if we misrepresented the proportion of pro-
tocol violations in the first ECASS, which were caused by
Dr Lev and colleagues respond:
failure of local investigators to recognize major early nonen-
We appreciate Dr von Kummer’s interest in our study of the hanced CT signs of infarction (3). Fifty-two represents ap-
benefits of soft-copy interpretation by using variable window proximately 48% of the 109 total protocol violations. The
width and center level settings in the nonenhanced CT de- statement that this group accounted for “more than half” of
tection of acute stroke (1). protocol violations was intended to convey that this group
Our objective in this study was to optimize the CT detec- comprised the majority of violators; the statement should
tion, but not necessarily the CT delineation, of hypoattenu- have read “almost half.”
ating ischemic regions in patients with acute stroke. We The images shown in figures 1 and 2 (1) have been
think that the readers of Radiology will agree that the conspi- presented by us at numerous conferences, along with other
cuity of the hypoattenuating regions seen in figures 1 and 2 similar examples, to audiences of neuroradiologists, gen-
of our article is increased by the use of nonstandard window eral radiologists, neurologists, and emergency department
width and center level review settings, which facilitates the physicians. It has been our uniform experience that the
rapid and definitive detection of these regions. Dr von Kum- overwhelming majority of those polled, regardless of their
mer may be correct in his assertion that the boundaries of the level of expertise at interpreting head CT scans, could
hypoattenuating areas in figure 2, once detected, can be more correctly identify the hypoattenuating, ischemic hemi-
precisely outlined by using standard, rather than nonstand- sphere only when presented with images displayed with
ard, review settings—possibly because of the more grainy, the nonstandard, and not the standard, review settings.
noisy quality of the images displayed with the nonstandard Although not addressed in our study, it has been shown
settings. However, this was not at issue in our study. that even brief periods of training can increase the accu-
Although Dr von Kummer’s observation regarding figure racy of stroke detection with CT (4). An increased aware-
2a of our article is correct—the caption for this figure fails to ness of the value of nonstandard review settings could
mention the hypoattenuation of the left lenticular nuclei, further improve the ability of physicians to detect the early
insular cortex, and temporal cortex, in addition to the “min- CT changes of stroke, especially in the emergency setting.
imal area of hypoattenuation of the left caudate head,” Such an awareness might be of less importance to highly
which is mentioned—we strongly disagree with the sugges- trained neuroradiologists.
tion that this oversight calls into question our reported sen- Our data, as well as Dr von Kummer’s own observations on
sitivity and specificity values. The intent of figure 2 was to the imprecision in reading CT scans after acute stroke, sug-
demonstrate that the ischemic hypoattenuation in the left gest that we can improve our ability to detect the changes of
hemisphere is easier to detect by using nonstandard, rather acute stroke on nonenhanced CT scans. The data we present,
than standard, review settings; precisely defining the extent as well as our daily experience in a busy acute stroke program,
of that hypoattenuation was the goal of neither this figure clearly support our conclusion that “the detection of acute
nor our study. Indeed, our conclusion that the nonenhanced ischemic brain parenchyma with nonenhanced CT scanning
head CT “detection of ischemic brain parenchyma is facili- is facilitated by soft-copy visual review at a PACS [picture
tated by soft-copy review with variable window width and archiving and communication system] workstation by using
center level settings” is in keeping with the well-studied variable, nonstandard window width and center level set-
limitations of lesion detectability. In general, a difference of tings” (1).
at least three steps on a 128-step gray-scale image is required
for lesion detection; therefore, subtle differences in
References
Hounsfield units can be difficult to discern with standard
1. Lev MH, Farkas J, Gemmete JJ, et al. Acute stroke: improved
review settings (2). nonenhanced CT detection— benefits of soft-copy interpretation
With regard to sensitivity and specificity for stroke de- by using variable window width and center level settings. Radi-
tection, it is again the presence, and not the extent, of the ology 1999; 213:150 –155.
Volume 216 Number 3 Radiology 921

3. 2. Constable RT, Henkelman RM. Contrast, resolution, and detect- Gemmete, MD,§ George J. Hunter, MD,* and Syeda T.
ability in MR imaging. J Comput Assist Tomogr 1991; 15:297– Hossain, BS*
303.
3. Hacke W, Kaste M, Fieschi C, et al. Intravenous thrombolysis with
Departments of Radiology* and Neurology,† Massachusetts
recombinant tissue plasminogen activator for acute hemispheric General Hospital
stroke: the European Cooperative Acute Stroke Study. JAMA PO Box 9657, Boston, MA 02114-9657
1995; 274:1017–1025. e-mail: lev@nmr.mgh.harvard.edu
4. von Kummer R. Effect of training in reading CT scans on patient
selection for ECASS II. Neurology 1998; 51(suppl 3):50 –52. Department of Radiology, University of Medicine and
Dentistry of New Jersey, Newark‡
Michael H. Lev, MD,* R. Gilberto Gonzalez, MD, PhD,* Department of Radiology, University of Michigan Medical
Walter J. Koroshetz, MD,† Jeffrey Farkas, MD,‡ Joseph J. Center, Ann Arbor§
922 Radiology September 2000