The incidence and significance of multicentric noncontrast-enhancing lesions distant from a histologically-proven glioblastoma.

Improvements in imaging are increasing the detection of multiple lesions in the setting of glioblastoma. Occasionally distant non-enhancing lesions may be identified which have the appearances of a multicentric low-grade glioma. We aimed to determine the incidence, prognostic significance and diagnostic value of this appearance in new glioblastoma patients. Pre-operative MRIs of patients with a new diagnosis of glioblastoma were reviewed to identify multicentric non-enhancing lesions, defined as areas of FLAIR hyperintensity and mass effect, without post-contrast enhancement, separate from the histologically-proven glioblastoma. Patient survival was compared to glioblastoma patients without these appearances, and follow-up imaging was reviewed. Nine of 151 patients (6 %) had multicentric non-enhancing lesions. Their median survival of 183 days was significantly worse than the 278 days for patients without multicentric nonenhancing lesions (p = 0.025). Follow-up MRIs were performed in four patients. In one patient, there were several additional lesions, one of which developed evidence of necrosis within 22 days of presentation. In the other three patients, the multicentric lesions developed enhancement and evidence of necrosis within 1 year, and became confluent on FLAIR with the dominant lesion. The appearance of a multicentric non-enhancing lesion is an uncommon finding in glioblastoma, but a poor prognostic feature. These lesions progress faster than expected for a low-grade glioma and are thus likely to represent more advanced lesions than their appearances suggest. Confluence with the dominant lesion developing with time suggests that the tumor is more extensive than appreciated on imaging.