Fig. 1

The CT diagnosis of an abscess may be difficult. Images show an abscess in the floor of the mouth on axial contrast-enhanced CT (a), and on axial T1-weighted fat-suppressed MRI after gadolinium (b) from the same patient imaged within 24 h with both modalities. Subtle central hypodensity and faint rim enhancement can be seen on CT (a); this was, however, misinterpreted as cellulitis. A fluid collection is clearly defined within abnormal tissue enhancement on MRI (b), and diffusion-weighed imaging (DWI, not shown here) suggested purulence, which was confirmed by surgery