Multiple ring-enhancing lesions in the brain

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Identification of the cause of a brain mass is a crucial initial diagnostic step, which critically influences the choice of treatment modality and the prognosis. The differentiation of neoplastic from non-neoplastic neurological disease is especially important in the interpretation of imaging findings. One central diagnostic clue in the 44-year-old woman admitted in a severely impaired mental state characterized by stupor was on the brain MRI, which showed multiple, scattered, small, and ovoidshaped cystic lesions with ring-enhancement on the gadoliniumenhanced T1-weighted sequences. However, these findings could not be used to differentiate the presence of an abscess from that of cystic tumour. Another important finding, that these lesions were characterized by high signal intensity in the diffusion weighted images (DWI) and demonstrated reduced apparent diffusion coefficients (ADC), pointed to cytotoxic oedema. The restricted diffusion in the abscess results from the high viscosity of the proteinaceous fluid and the hypercellularity of the pus. Unlike abscesses, cystic tumours frequently show low signal intensity on DWI and high ADC values, although exceptions that can mimic brain abscess have also been found. Toxoplasmosis infection, which is generally associated with conditions causing immunocompromise, also demonstrates low signal intensity on DWI and