- Patients with a CNS lesion consistent with trilateral or stage 4b disease may be enrolled without tissue confirmation if (1) unequivocal leptomeningeal disease is present on brain or spine magnetic resonance imaging (MRI) scan and/or (2) the primary tumor is at least 2 cm in diameter, predominantly solid, and demonstrates enhancement on the post-gadolinium images; however, even in such cases surgery should be given serious consideration