Examples of tumefactive brain lesions and relevant MRI features for the differential diagnosis of patients with MOGAD, MS, and AQP4+NMOSD

Unless otherwise specified, lesions are shown on axial T2-fluid-attenuated inversion recovery (T2-FLAIR). Tumefactive lesions are indicated by white arrows, while specific features are indicated by arrowheads.

(Panel A) MOGAD: Tumefactive lesions in the bilateral hemispheric white matter (A.a, arrows); bilateral tumefactive lesions in the corticospinal tract and thalami (A.b, arrows); tumefactive lesion involving the entire pons (A.c, arrow) without evidence of T2-hypointense rim, diffusion restriction (ie, no DWI hyperintensity), and no ADC map hypointensity (A.c); bilateral tumefactive lesions in the middle cerebellar peduncles (A.d, arrows), with complete resolution at follow-up MRI (A.e).

(Panel B) MS: Baló-like tumefactive lesions in the hemispheric white matter (B.a, arrow) and periventricular white matter (B.b, arrow); tumefactive lesion located in the hemispheric white matter, showing a complete T2-hypointense rim (arrowhead) with a corresponding ring of peripheral diffusion restriction, as indicated by the hyperintensity in DWI (arrowhead) and hypointensity on ADC map (arrowhead) (B.c); tumefactive lesion in the left middle cerebellar peduncle (B.d, arrow) undergoing volumetric reduction, but still present at follow-up MRI (B.e, arrow).

(Panel C) AQP4+NMOSD: Tumefactive lesions in the hemispheric white matter (C.a, arrow), corticospinal tract (C.b, arrow); tumefactive periventricular lesion extensively involving the splenium of the corpus callosum in an "arch-bridge" pattern (C.c, arrow); the lesion does not show any T2-hypointense rim and is characterized by DWI hyperintensity of the splenium (arrowhead) with focal diffusion restriction (ie, corresponding hypointensity on the ADC map, arrowhead); tumefactive lesion involving the entire pons (C.d, arrow), showing residual mild hyperintensity near the fourth ventricle (C.e, arrow).