© Pol J Radiol, 2011; 76(2): 13-17 Ambrosius W et al – Hyperdense posterior cerebral artery sign in ischemic stroke Figure 1. The HPCA sign on CT. Examples of the HPCA sign (A–D, marked by the white narrows) in proximal and distal parts of the P2 segment with the corresponding ischemic lesions (A’–D’ respectively). The infarct areas marked by contours in white. 19 cm3, median 17.3 cm3) compared to those without this feature (mean 8.9 cm3, median 4.3 cm3; p=0.02). The secondary hemorrhage appeared significantly more frequ- ent in the group with manifestation of HPCA sign compared to the patients without this symptom (p=0.03). We did not find any significant differences in age, sex, conventional risk factors, baseline NIHSS score and most of biochemical parameters between patients without or with the HPCA sign, except C-reactive protein (CRP) and fibrino- gen. In the univariate analysis levels of those two markers were significantly higher in patients with the presence of the HPCA sign than in those lacking this sign (p=0.02 for both factors). The association between higher hematocrit values and the hyperdensity of the PCA with borderline significance (p=0.05) was also observed. The results of multivariable analysis are shown in Table 2; only the infarct’s volume was an independent factor related to the presence of the HPCA sign. The statistical trend was obse- rved between the presence of the HPCA sign and the occur- rence of a secondary hemorrhage in CT scans (p=0.07) and hematocrit (p=0.05). The overall prediction of this model was 90.2% correct (100% for the absence of HPCA class and 54.5% for the presence of HPCA class). Discussion In our study the HPCA sign was observed among 22% patients who experienced PCA territory stroke and had noticeable acute infarcts lesions in CT in comparison to 35.4% given by a similar report [6], however, the discrepan- cy could arise from a different methodology used. We stu- died consecutively admitted patients with stroke and visi- ble ischemic changes in CT, whereas the mentioned study had a retrospective character in which the authors were particularly interested in finding frequency of the HPCA sign. Additionally, in our study we reviewed a larger (more than twice the number) group of patients. The agreement between the raters was very good, howe- ver, variations in interpretation were mostly because of the course and diameter of the vessel (in older patient in whom the basilar artery can be elongated and kinked and thus mimics the PCA) and localization within the cistern (closed to the brain stem which causes difficulty in inter- pretation, especially with a possible partial volume effect from nearest bone structures). According to many studies, the incidence of the hyperdense MCA sign is variable. Most often it fluctuates up to 30% of initial CT scans in patients with acute ischemic stro- ke [10,11]. In our study, the HPCA sign is observed in 22% of CT scans carried out in posterior circulation infarction patients. Presumably the difference is the result of more heterogeneous etiology of posterior circulation stroke than in anterior circulation infarction. It is believed those car- diac and intra-arterial embolisms are the leading mechani- sms [12]. Specific relations among the vertebrobasilar sys- tem cause that the emboli mostly arrest not in the PCA but in the distal parts of the basilar artery or vertebral artery [5]. Other studies showed that also atherosclerotic plaques localized in the PCA are relatively rare (comparing to the basilar and vertebral arteries) [13,14]. A standard CT scanning procedure has the orbito-meatal orientation (which not always properly visualizes the posterior cerebral arteries) could be the additional reason of a HPCA sign low detection [6]. Our study discovered that in the group of patients with the HPCA sign the infarct volume was larger compared to patients which did not present this feature. This association seems independent from other factors and is consistent with the results of the earlier study [6]. However, the advantage of our analysis is an accurate quantitative measurement of lesion’s absolute volume whereas Krings et al estimated the size of infarct by qualitative 3-point scale. The data about association between a well know hyperdense MCA sign and 15