© Pol J Radiol, 2011; 76(2): 13-17 Ambrosius W et al – Hyperdense posterior cerebral artery sign in ischemic stroke explanation is that the use of NIHSS in posterior circula- tion stroke appears to have some inaccuracy [22,23]. As until now there is no recognizable clinical scale particularly suited to stroke in the posterior circulation, we thus applied commonly used measures. Our study has some limitations as all clinical data (demographics, risk factors, comorbid conditions, neurological status) were assessed prospectively except the CT scans analysis which had a retrospective cha- racter. Unfortunately, we did not have any other reference method for visualization intra-arterial pathology (like MR or CT angiography), however, our study is based on a routi- ne clinical practice with stroke patients in most ED set- tings. Differentiating the HPCA sign from other conditions: above mentioned partial volume effect (from bones) and calcifications of dura mater are critical. Checking the neigh- boring slices with analysis of artery course and dura loca- tion can help in resolving the problem. The calcified athe- rosclerosis in vessels also should be considered. The calci- fications of arteries have usually a higher density, and are permanent as opposed to temporal persistence of thrombus which is asymmetrical and undergoes resolving (with the disappearance of the HPCA sign in serial CT scans). References: 1. Rosso C, Drier A, Lacroix D et al: Diffusion-weighted MRI in acute stroke within the first 6 hours: 1.5 or 3.0 Tesla? Neurology, 2010; 74(24): 1946–53 2. Thomalla G, Rossbach P, Rosenkranz M et al: Negative fluid- attenuated inversion recovery imaging identifies acute ischemic stroke at 3 hours or less. Ann Neurol, 2009; 65(6): 724–32 3. Guidelines for management of ischaemic stroke and transient ischaemic attack. Cerebrovasc Dis, 2008; 25(5): 457–507 4. 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