Figure 4c. Perisinus abscess in an 18-month-old girl with left acute mastoiditis. (a, b) Axial CT scans of the temporal bone show increased attenuation of the left mastoid air cells with subtle erosion of the mastoid cortex (arrow in a) and superior sigmoid plate (arrow in b). (c, d) Axial unenhanced (c) and contrast-enhanced (d) cranial CT scans show an unsuspected small epidural abscess (arrow). The ipsilateral sigmoid sinus (S) demonstrated normal enhancement on CT scans and normal flow void on T2-weighted MR images. (e) Posterior coronal MR venogram shows slightly diminished venous flow with decreased size of the left sigmoid sinus.