Fig. 5

Pitfalls in the interpretation of diffusion restriction in ring-enhancing brain lesions. Top row (A-D) shows a heterogeneous T2-hyperintense lesion in the left parietal lobe (A) with the appearance of ring-enhancement on post-contrast T1-weighted imaging (B), central high signal on DWI (C), with corresponding low ADC (D) indicating restricted diffusion. While diffusion restriction suggests an abscess, the diagnosis was a lobar haemorrhage. Bottom row (E–H) shows a T2-hypointense lesion in the left cerebellum (E) with ring-enhancement on post-contrast T1-weighted imaging (F). The central portion of the lesion shows an intermediate DWI signal (G) and ADC (H). Despite a lack of diffusion restriction, the diagnosis was a toxoplasmosis abscess. Especially in abscesses from atypical organisms (e.g., toxoplasmosis and tuberculosis), diffusion is not always restricted