Incidence and imaging follow up of lesions consistent with a low grade glioma distant from a histologically proven glioblastoma.

PURPOSE: To determine the incidence of additional lesions consistent with low grade glioma in patients with a new diagnosis of glioblastoma, with subsequent imaging follow-up. MATERIALS AND METHODS: Institutional Human Research Ethics Committee approval was obtained. Patients with a new diagnosis of glioblastoma between September 2007 and December 2010 were identified. Only patients with at least FLAIR (fluid attenuated inversion recovery) and post-contrast sequences were included. Pre-operative Magnetic Resonance Imaging (MRI) studies were reviewed together by two readers to determine whether there were lesions with imaging appearances consisting with a low grade glioma separate from the dominant tumour (ie. multicentric lesions on imaging). This was based primarily on the FLAIR sequence, with the diagnosis being made on the presence of cortical signal hyperintensity and mass effect, without post-contrast enhancement. RESULT(S): 9 of 151 patients (6%) had lesions consistent on imaging with a low grade glioma separate from the dominant tumour. Their median survival was 183 days, compared to 264 days for patients without this feature. This worse survival was statistically significant on multivariate analysis (p=0.024). There was a high incidence of multiple enhancing lesions separate from the focus of low grade tumour, occurring in 5 of these 9 patients. Excluding studies performed immediately post-operatively, follow-up MRIs were performed in three patients. In all three, these additional areas of tumour developed enhancement and evidence of necrosis within one year, and became confluent on FLAIR with the dominant lesion. In a fourth patient, a further separate lesion had developed evidence of necrosis in the 22-day interval between the full diagnostic study and the limited postcontrast study performed for stereotaxis. CONCLUSION(S): The presence of a low grade glioma separate from the dominant lesion is an uncommon finding in glioblastoma, but likely to be useful i