Imaging description

Non-contrast head CT is often the first study for evaluation of acute cognitive decline in the emergent setting. Tumefactive multiple sclerosis (TMS) typically shows a large area of confluent hypodensity in the periventricular white matter, often extending from the body of the corpus callosum. This area of hypodensity can extend to the subcortical white matter and, in some cases, exhibit mass effect on the neighboring ventricle, distorting the overlying cortex. While tumefactive lesions can be large enough to exhibit some mass effect, the mass effect is often less than would be expected for the size of the lesion. Post-contrast images can show subtle, discontinuous edge enhancement (Figure 12.1A).

Further characterization with MRI (Figure 12.1B–E) usually reveals the characteristic imaging findings associated with TMS that differentiate it from other diseases. The confluent hypodensity seen on CT will correlate to a similar territory of intrinsic hypointensity on T1-weighted images. There will be corresponding central hyperintensity with a thin edge of hypointensity on T2-weighted images. Post-contrast MRI yields a characteristic horseshoe-shaped leading edge of enhancement that is open towards the cortex. Corresponding restriction on diffusion-weighted imaging (DWI) occurs in the region of enhancement (Figure 12.1F) [1, 2].