“…This situation is not uncommon. In the Duke Box 1 MRI findings in histologically proven PACNS Normal 25,37 Progressive confluent white matter lesions [66][67][68][69][70][71][72][73][74] Cortical and subcortical T2 lesions [75][76][77] Multiple diffusion-positive lesions 78,79 Large intraparenchymal hematoma 80 Multiple microhemorrhages 66,72,81 Multiple small enhancing lesions 71,78,82 Large single and multiple enhancing mass lesions 26,50,[83][84][85][86] Enhancing small-vessel walls/small perivascular spaces 69,70,87,88 Leptomeningeal enhancement 14,77 Powers series, 5 of 30 biopsies were nondiagnostic. 11 In the Johns Hopkins series, 35 of 41 and in the University of Michigan series, 15 of 61 had a nondiagnostic biopsy.…”