Diffusion-weighted images of intracranial cyst-like lesions

Magnetic resonance sequences may be designed to evaluate the diffusion move ments of the protons (diffusion-weighted images, DWI). In these images, a b right signal identifies a region where the diffusion along a spatial axis i s restricted. The contents of a cystic lesion frequently have the signal in tensities of a generic homogeneous hyperproteinic fluid (hypointensity in T 1-, hyperintensity in T2-weighted images). DWI may give further information about the microscopic organisation of these fluids: a hyperintense signal indicates the presence of a restricted diffusion, due to some kind of micro scopic organisation, at the cellular or macromolecular level. This may prov ide additional information useful for clinical purposes. We obtained DWI in 24 consecutive patients with intracranial cystic lesions, (19 intra-axial: five abscesses, five gliomas, six metastases, two demyelinating lesions, o ne neurocysticercosis; five extraaxial: two arachnoid cysts, two epidermoid cysts, one cholesteatoma). We found a strongly hyperintense signal, indica ting restricted diffusion, in brain abscesses, epidermoid cysts and cholest eatoma; all the remaining lesions were hypointense or mildly hyperintense. We found these data useful in critical diagnoses, such as in differentiatin g abscesses from tumours, and in identifying elusive tumours such as epider moid cysts.