A ring-enhancing metastasis with central high signal on diffusion-weightedimaging and low apparent diffusion coefficients

Diffusion-weighted imaging (DWI) has been reported to be useful in the diff erential diagnosis between abscesses and cystic or necrotic tumours. Howeve r, experience is still limited and the true sensitivity and specificity rem ain to be determined. Our purpose is to describe a ring-enhancing metastasi s of adenocarcinoma with a DWI pattern similar to that reported for abscess es. The tumour had a diameter of 1.5 cm and give signal from its centre sim ilar to that of normal brain on T1-weighted images, whereas it was increase d on T2-weighted images, and surrounded by a low signal ring, suggesting a capsule. The signal was high on DWI and the apparent diffusion coefficient (ADC) was low (0.55 x 10(-3) mm(2)/s). The findings were misinterpreted as representing an abscess in the early capsule-formation stage, but the signa l pattern probably represented early tumour necrosis with intracellular oed ema, but without liquefaction. Findings on DWI during the early capsule for mation stage in abscesses and early tumour necrosis are probably similar an d must be interpreted with caution.