Pictorial Essay D Fig. 1.-21-year-old woman presenting with new-onset seizure and biopsy-proven tumefactive demyelinating lesion. A, Enhanced axial T1-weighted spin-echo image reveals large left frontal lesion with incomplete ring of enhancement (arrow), open on gray matter side of lesion. There is faint enhancement within dilated, centrally located venous structures (arrowhead), suggestive of demyelinating lesion. B, Enhanced coronal T1-weighted spin-echo image reveals large left frontal lesion with incomplete ring of enhancement (arrow). C, Unenhanced axial T2-weighted spin-echo image reveals relatively little mass effect or surrounding vasogenic edema given size of lesion.