Inadequate Acoustical Temporal Bone Window in Patients with a Transient Ischemic Attack or Minor Stroke: Role of Skull Thickness and Bone Density

Transcranial Doppler (TCD) ultrasonography may provide important diagnostic and prognostic information in patients with ischemic stroke or transient ischemic attack. TCD also enhances the effect of thrombolytic treatment in patients with acute stroke. In some patients, especially elderly women, TCD cannot be performed because of temporal bone window failure (WF). We investigated whether skull thickness or bone density on computed tomography scans predicts WF. In 182 patients with a transient ischemic attack or minor ischemic stroke, skull thickness and bone density measurements were made at the level of the temporal bone window. Multiple logistic regression analysis was used to relate independent variables to WF and to adjust the estimates for possible confounding factors. TCD signals were absent on the symptomatic side in 22 female and 11 male patients (18%). Both skull thickness and radiodensity at the level of the temporal bone window were strongly related to WF as well as age and female gender. After adjustment according to age and gender, skull thickness at the temporal bone window was an independent prognostic factor of WF (odds ratio [OR]: 2.3 per mm increase in skull thickness, 95% confidence interval [CI]: 1.4 to 3.8). Radiodensity of the temporal bone decreased with age in women (-52 HU per 10 y over 50 y of age, 95% CI: -73 to -30) but in men (-10 HU per 10 y over 50 y of age, 95% CI: -33 to 13), no statistically significant association was observed. We computed probabilities of WF for each patient individually. With a probability cut point of 50%, 33% of the patients with WF and 97% of the patient without WF were correctly identified. The area under the receiver operating characteristic (ROC) curve of this simple prediction model including age, gender and skull thickness was 0.88; the area under the ROC curve of a gender-stratified model including age, skull thickness and radiodensity was 0.90. This difference was not statistically or clinically significant p = 0.13). WF is more common in women because density of the temporal bone in elderly women is low. Absence of WF can be predicted by a combination of three simple parameters: skull thickness, age and gender. This may help to select patients with ischemic stroke for diagnostic TCD screening and to facilitate targeted delivery of ultrasound-enhanced thrombolysis. (E-mail: a.wijnhoud@erasmusmc.nl).

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