The pseudo-delta sign is unreliable in differentiating between aneurysmal SAH and sinus thrombosis in unenhanced brain CT

Abstract

The pseudo-delta sign (PDS) consists of a hyperdense extra-axial triangular image surrounding the low density of the superior sagittal sinus (SSS) in the unenhanced brain CT scan (Fig. 1) [1]. The true delta or empty-delta sign, described by Buonanno et al. in 1978, is only visible on contrast-enhanced films (Fig. 2) [1–4]. The PDS has been described in association with interhemispheric subdural hemorrhage, subarachnoid hemorrhage (SAH) and superior sagittal sinus thrombosis (SSST) [1–5]. The sign has also been encountered with increased attenuation of normal dura surrounding the SSS, diffuse cerebral edema in children and sluggish flow resulting from raised intracranial pressure. Others include calcification of arachnoid granulations and possibly brain death [3,4,6–8]. In an autopsy study of 12 patients with ‘empty triangle sign’, another descriptive term for the PDS, Zilkha et al. found that five of of the patients had SSST. However, they noticed that this sign was not specific for SSST as it was also observed in SAH [3]. The aim of this study was to compare the frequency of PDS in our patients with SAH, SSST as well as in other neurological conditions and to infer its diagnostic accuracy.