Early postoperative MRI overestimates residual tumour after resection of gliomas with no or minimal enhancement

Standards for residual tumour measurement after resection of gliomas with no or minimal enhancement have not yet been established. In this study residual volumes on early and late postoperative T2-/FLAIR-weighted MRI are compared. A retrospective cohort included 58 consecutive glioma patients with no or minimal preoperative gadolinium enhancement. Inclusion criteria were first-time resection between 2007 and 2009 with a T2-/FLAIR-based target volume and availability of preoperative, early (<48 h) and late (1-7 months) postoperative MRI. The volumes of non-enhancing T2/FLAIR tissue and diffusion restriction areas were measured. Residual tumour volumes were 22% smaller on late postoperative compared with early postoperative T2-weighted MRI and 49% smaller for FLAIR-weighted imaging. Postoperative restricted diffusion volume correlated with the difference between early and late postoperative FLAIR volumes and with the difference between T2 and FLAIR volumes on early postoperative MRI. We observed a systematic and substantial overestimation of residual non-enhancing volume on MRI within 48 h of resection compared with months postoperatively, in particular for FLAIR imaging. Resection-induced ischaemia contributes to this overestimation, as may other operative effects. This indicates that early postoperative MRI is less reliable to determine the extent of non-enhancing residual glioma and restricted diffusion volumes are imperativ

Early metabolic responses in temozolomide treated low-grade glioma patients

Amino acid transport and protein synthesis are important steps of tumor growth. We investigated the time course of tumor metabolism in low-grade gliomas (LGG) during temozolomide chemotherapy, and compared metabolic responses as measured with positron emission tomography (PET) with volume responses as revealed by magnetic resonance imaging (MR). A homogeneous population of 11 patients with progressive non-enhancing LGG was prospectively studied. Imaging was done at 6-months intervals starting six months, and in a second series starting three months after treatment initiation. F-18 fluoro-ethyl-l-tyrosine (FET) uptake was quantified with PET as metabolically active tumor volume, and was compared with the tumor volume on MR. Response was defined as ≥10% reduction of the initial tumor volume. Eight patients showed metabolic responses. Already 3 months after start of chemotherapy the active FET volumes decreased in 2 patients to a mean of 44% from baseline. First MR volume responses were noted at 6 months. Responders showed a volume reduction to 31 ± 23% (mean ± SD) from baseline for FET, and to 73 ± 26% for MR. The time to maximal volume reduction was 8.0 ± 4.4 months for FET, and 15.0 ± 3.0 months for MR. The initial metabolic response correlated with the best volume response on MR (Spearman Rank P = 0.011). Deactivation of amino acid transport represents an early indicator of chemotherapy response in LGG. Response assessment based on MR only has to be reconsidered. The time window obtained from PET may assist for individual treatment decisions in LGG patients