Contrast-Enhanced Transcranial Color-Coded Sonography in Acute Cerebral Infarction
To the Editor:
Postert and colleagues1 reported their successful use of an echo-contrast agent in transcranial color-coded sonography (TCCS) to overcome the problem of inadequate acoustic bone windows (IABW) in patients with acute ischemic stroke affecting the middle cerebral artery territory. Their results were both convincing and impressive, and CT angiography (CTA) was used as a gold standard for comparison in a subgroup of patients. Adding a galactose-based echo-enhancing agent permitted an adequate sonographic examination of the middle cerebral artery in 74 of 90 stroke patients (82%) with proven IABW.1 Two features of contrast-enhanced TCCS (CE-TCCS) are noteworthy: completion of the examination of the major arteries around the circle of Willis within 10 minutes; and feasibility of repeated examinations. I wish to raise the following issues for clarification and discussions by the authors.
First, some exclusion criteria were indicated in the article, but the number of patients excluded was not mentioned.1 Although I understand the rationale behind these exclusion criteria, I am interested in knowing how many patients were excluded because of galactosemia. More importantly, what adverse reactions may occur if 4 g of galactose-based microbubbles is inadvertently injected into a patient with galactosemia? In addition, excluding patients with a history of cerebrovascular diseases or old ischemic lesions on CT scans may limit the applicability of CE-TCCS in patients with acute cerebral infarction.
Second, follow-up CT scan was performed within 7 days. In the subsection “CT and CTA,” CT findings were used to classify the extent of infarction involving the middle cerebral artery territory.1 I assume that the findings of the follow-up CT scan but not the initial CT scan were used in the classification. I am interested in knowing the shortest time interval between the 2 CT studies, because the full extent of cerebral infarction might not be appreciated if the second CT scan was performed soon after the first study. In addition, a description of the initial CT findings and the evolution of the CT findings may illustrate the predictive value of visualization of the middle cerebral artery.
Finally, the treatment time window for thrombolysis is short.2 3 4 One major limitation of conventional transcranial Doppler is the relatively long examination time, and the presence of IABW is rather common.5 Would the authors recommend CE-TCCS as the first-line transcranial sonographic study rather than wasting previous time with transcranial Doppler or unenhanced TCCS? On the other hand, CTA can reliably and quickly visualize the major arteries around the circle of Willis. I wonder whether adding CTA to an initial CT scan is a better tool to triage patients for acute thrombolysis, and serial contrast-enhanced TCCS may be used to monitor the middle cerebral artery when occlusion is seen on CTA.
- Copyright © 2000 by American Heart Association
Postert T, Braun B, Meves S, Köster O, Przuntek H, Weber S, Büttner T. Contrast-enhanced transcranial color-coded sonography in acute hemispheric brain infarction. Stroke. 1999;30:1819–1826.
Adams HP Jr, Brott TG, Furlan AJ, Gomez CR, Grotta J, Helgason CM, Kwiatkowski T, Lyden PD, Marler JR, Torner J, Feinberg W, Mayberg M, Thies W. Guidelines for thrombolytic therapy for acute stroke: a supplement to the guidelines for the management of patients with acute ischemic stroke. Stroke. 1996;27:1711–1718.
Cheung RT. Predicting early deterioration or improvement in ischemic stroke by transcranial Doppler. Stroke. 1998;29:2443–2444. Letter.
We thank Dr Cheung for his interest in our article on CE-TCCS in acute stroke. In our study, 7 patients with insufficient temporal bone window had to be excluded because of previous infarction in the middle cerebral artery territory. The rationale behind this exclusion criterion was the fact that middle cerebral artery flow velocities in acute stroke patients may be considerably influenced by hemodynamic alterations due to old ischemic lesions. It is well known and could be confirmed in our study that a major part of acute stroke patients with middle cerebral artery mainstem or branch occlusions exhibit partial or complete recanalization of these vessels within the first days (R1 R2 ). However, larger studies on the long-term follow-up of transcranial Doppler examinations in stroke patients have not been performed. In our experience, individuals with large middle cerebral artery infarctions in the past frequently show reduced flow velocities and vessel pulsatilities as compared to the unaffected side.
In our department we have performed CE-TCCS examinations since 1996 and have never observed a serious adverse event in any patient. In addition, no such case has been published in the literature. In screening studies, the incidence of galactosemia was between 4 and 10 per 100 000 newborns.R3 R4 In clinical practice, the probability of a galactose-based microbubble injection in a stroke patient who suffers from galactosemia seems to be very low. However, because such an injection may cause transient deterioration of neurological, hepatic, or other symptoms, careful evaluation of medical history is important.
We agree that early performance of follow-up CT examinations may lead to underestimation of the final infarction size. For this reason, we selected relatively long time intervals between the acute and follow-up examinations. In our study, the shortest time interval was 5 days.
In contrast to transcranial Doppler, TCCS allows rapid and reliable identification of intracranial arteries using the 2-dimensional B-mode image of brain parenchyma. This advantage is particularly important in patients suitable for thrombolysis or in agitated subjects. For this reason, we would recommend unenhanced TCCS examinations as the first-line imaging mode, when corresponding probes and experienced examiners are available. However, if intracranial arteries cannot be identified sufficiently, echo-contrast agent application should follow promptly in those centers experienced in CE-TCCS. Using CE-TCCS, diagnostically useful results can be obtained in >90% of all stroke patients, clearly exceeding the number of successful transcranial Doppler examinations in the same patients (5).
We are in accord with Dr Cheung that CT angiography may represent a reliable and quick alternative for the assessment of the vascular state of acute stroke patients. However, availability of spiral CT scanners is still limited, application of contrast agents is not possible in individuals with renal failure, and, more than in CE-TCCS, reliability of this method highly depends on the cooperation of the patient. In all those cases, CE-TCCS is an excellent method to identify patients with occlusions of the major intracranial arteries. In the follow-up phase, CE-TCCS allows timesaving and bedside monitoring of the intracranial vessels, particularly in critical ill patients.
Postert T, Braun B, Meves S, Köster O, Przuntek H, Weber S, Büttner T. Contrast-enhanced transcranial color-coded sonography in acute hemispheric brain infarction. Stroke.. 1999;30:1819–1826.
Ringelstein EB, Biniek R, Weiller C, Ammeling B, Nolte PN, Thron A. Type and extent of hemispheric brain infarction and clinical outcome in early and delayed middle cerebral artery recanalization. Neurology.. 1992;42:289–298.
Honeyman MM, Green A, Holton JB, Leonard JV. Galactosemia: results of the British paediatric surveillance unit study, 1988–1990. Arch Dis Child.. 1993;69:339–341.
Goertler M, Kross R, Baeumer M, Jost S, Grote R, Weber S, Wallesch CW. Diagnostic impact and prognostic relevance of early contrast-enhanced transcranial color-coded duplex sonography in acute stroke. Stroke.. 1998;29:955–962.