Specific Imaging Findings

Mass-like features of multiple sclerosis and other demyelinating processes are referred to as tumefactive demyelinating lesions (TDLs). TDLs are typically located in the cerebral white matter ranging from 1 to over 10 cm in size. They may be unifocal; however, additional lesions are usually either present or occur over time. Edema surrounds most TDLs, but is usually very mild, and mass effect is typically even less prominent. The lesions are T1 hypointense in the center and their periphery may be brighter on magnetization transfer imaging. Almost all TDLs enhance with contrast, which may co-localize with a T2 hypointense rim. Incomplete rim enhancement (“open ring”), along with mixed T2 iso- and hyperintensity of the enhancing components, absence of cortical involvement, and absence of mass effect are highly specific for TDL, but not always present. Vessel-like structures, presumably veins, running through the lesion are typical but only occasionally seen. Other characteristic features are bright peripheral rim on DWI (dark on ADC maps) and relatively low rCBV on perfusion studies. CT hypodensity of the enhanced regions on MRI (the MRI enhancing rim is not discernible on non-enhanced CT) is also very specific. Marked elevation of glutamate and glutamine (Glx, at 2.1–2.5 ppm) are characteristically present on short echo time (TE around 30 ms) MR spectroscopy. Nonspecific findings are commonly observed with intermediate echo times.