Early CT changes of ischemia: limitations of what we know.

Worldwide, CT scanning is by far the most available early CT changes, and both are correlated with worse imaging modality for evaluating acute stroke patients, and outcome. Whether the presence of early CT changes adds we have more data about the reliability and utility of CT in substantially more certainty about outcome than what we this setting than for any other imaging technique. Drs can conclude simply from a carefully quantitated neuroFiorelli and colleagues have added to our database by their logical exam (for instance by using the National Institutes evaluation of baseline CT scans in 158 patients with of Health Stroke Scale) requires careful statistical analysis suspected anterior circulation ischemia [1]. They found and remains, in my mind, uncertain. To make matters even that CT is reasonably sensitive to tissue damage since early more uncertain, recent studies have shown that abnorchanges of ischemia were detected in 49% of patients malities on diffusion-weighted MRI can be reversed by imaged within 5 h of symptom onset. They also found that reperfusion [2]. No such studies are available for early CT CT was reasonably accurate since the detected abnorchanges of ischemia, but if the same were true, early CT malities were almost always predictive of the ultimate changes might mislead the clinician into assuming (premainfarction except when early changes were limited only to turely) that the prognosis is poor. subcortical structures; of 27 such scans, infarction ultiA second problem is the reliability in recognizing and mately evolved to include both subcortical and cortical quantitating early CT changes of ischemia. The NINDS structures in 15. Finally, they found that the presence of group has recently published their data showing that interearly CT abnormalities were predictive of worse outcome. observor agreement was only ‘fair’ in detecting and Although the exact percentages differ somewhat from quantitating hypoattentuation of the CT signal on scans other studies, these findings are consistent with previous obtained within 3 h of stroke onset [3]. While others have studies and clinical experience. shown better agreement, and while it may be easier to Although such data are reassuring, we must not overagree on scans obtained later in the course after the state the information that CT provides, rely too heavily on changes are more obvious, uncertainly will undoubtedly the ‘shadows’ that we perceive on the CT images, nor remain about interpretation of individual CT scans. For should we jump to conclusions when applying this ininstance, when I looked at Fig. 1a, without reading the formation to clinical decision-making. figure legend, I would have said that in addition to First, it is still uncertain that early CT changes tell us subcortical changes, there is also effacement of cortical substantially more about long term clinical outcome than sulci, especially in the peri-sylvian region. If indeed CT is does simply quantitating the severity of the initial neuroimportant in decision-making, we need to make our logical deficit. The authors state that they adjusted for identification and quantitation of early CT changes more clinical severity on admission in their analysis finding that objective and reliable. more patients with CT changes died or were left disabled, Finally, it is extremely important to recognize that we but it is not clear how they determined baseline stroke still do not know the extent (if any) of early CT changes of severity or how it was factored into the analysis. Patients ischemia which should preclude administration of thromwith worse neurological deficit have a higher incidence of bolytic therapy if the patient otherwise qualifies. At least in the U.S. and Canada, the only approved use of thrombolysis is intravenous rtPA given within 3 h of stroke *Tel.: 11-713-500-7100 (x7092); fax: 11-713-500-7090 or 7019. E-mail address: jgrotta@neuro.med.uth.tmc.edu (J. Grotta) symptom onset, based on results of the NINDS rtPA Stroke