Imaging description

Demyelinating lesions are usually small and multiple. Occasionally demyelinating lesions can mimic neoplasms clinically, radiologically, and even histologically – hence the name tumefactive demyelinating lesion (TDL). TDLs usually present as large white matter lesions in the periventricular or subcortical regions [1]. In particular, solitary TDLs are often misdiagnosed as tumor, leading to unnecessary biopsy, surgery, and delay in treatment.

While TDLs show a spectrum of imaging abnormalities, certain features are commonly seen, and these help in differentiating TDLs from other lesions [2,3]. On CT, TDLs show hypoattenuation [4]. On post-contrast MRI, incomplete ring enhancement is a relatively characteristic feature, which may be present up to 70% of patients (Figs. 18.1, 18.2). The T2 signal is variable, but most lesions show a markedly increased T2 signal centrally and relatively decreased signal peripherally. Up to 50% of TDLs do not have mass effect or edema, which is a critical observation in differential diagnosis. When mass effect and/or edema present they are usually less pronounced than what would be expected from a high-grade glioma of similar size, although occasionally marked mass effect can be seen. Diffusion-weighted imaging (DWI) signal is also variable across the lesions, with central parts showing increased diffusivity and peripheral potions showing relative restricted diffusion (Fig. 18.1).