Accurate determination of the extent and grade of adult-type diffuse gliomas is critical to patient management. In clinical practice, contrast-enhancing areas of diffuse gliomas in magnetic resonance imaging (MRI) sequences are usually used to target biopsy, surgery, and radiation therapy, but there can be discrepancies between these areas and the actual tumor extent. Here we show that adding 18F-fluoro-ethyl-tyrosine positron emission tomography (FET-PET) to MRI sequences accurately locates the most malignant areas of contrast-enhancing gliomas, potentially impacting subsequent management and outcomes. We present a prospective analysis of over 300 serial biopsy specimens from 23 patients with contrast-enhancing adult-type diffuse gliomas using a hybrid PET-MRI scanner to compare T2-weighted and contrast-enhancing MRI images with FET-PET. In all cases, we observe and confirm high FET uptake in early PET acquisitions (5–15 min after 18F-FET administration) outside areas of contrast enhancement on MRI, indicative of high-grade glioma. In 30% cases, inclusion of FET-positive sites changes the biopsy result to a higher tumor grade.

Neuroimaging based on O-[2-(18F)fluoroethyl]-l-tyrosine (FET)-PET provides additional information on tumor grade and extent compared with MRI. Dynamic PET for biopsy target selection further improves results but is often clinically impractical. Static FET-PET performed at two time-points may be a good compromise, but data on this approach are limited. The aim of this study was to compare the histology of lesions obtained from two challenging glioma patients with targets selected based on hybrid dual time-point FET-PET/MRI. Five neuronavigated tumor biopsies were performed in two difficult cases of suspected glioma. Lesions with (T1-CE) and without contrast enhancement (T1 and T2-FLAIR) on MRI were selected. Dual time-point FET-PET imaging was performed 5–15 min (PET10) and 45–60 min (PET60) after radionuclide injection. The most informative FET-PET/MRI images were coregistered with MRI in time of biopsy planning. Five biopsy targets (three from high uptake and two from moderate uptake FET areas) thought to represent the most malignant sites and tumor extent were selected. Histopathological findings were compared with FET-PET and MRI images. Increased FET uptake in the area of non-CE locations on MRI correlated well with high-grade gliomas localized as far as 3 cm from T1-CE foci. Selecting a target in the motor cortex based on FET kinetics defined by dual time-point PET resulted in a grade IV diagnosis after previous negative biopsies based on MRI. An additional grade III diagnosis was obtained from an area of glioma infiltration with moderate FET uptake (between 1 and 1.25 SUV). These findings seem to show that dual time-point FET-PET-based biopsies can provide additional and clinically useful information for glioma diagnosis. Selection of targets based on dual time-point images may be useful for determining the most malignant tumor areas and may therefore be useful for resection and radiotherapy planning.

Intraoperative CT is a very useful tool in spine surgery as well as in functional neurosurgery and neurooncology.

Accurate determination of the border and grade of malignant gliomas is critical to patient management. Contrast-enhancing areas in MRI sequences of malignant gliomas are a target for biopsy, surgery, and radiation therapy, but there can be discrepancies between these areas and the actual extent of tumor. Here we prospectively collected over 400 serial biopsy specimens from 23 patients with contrast-enhancing high-grade gliomas using hybrid PET-MRI sequences to assess the utility of this imaging approach for obtaining accurate biopsies. In 35% cases, the biopsy result was changed to a higher tumor grade after the inclusion of FET-positive sites. In all cases, high FET uptake was visualized and confirmed outside areas of contrast enhancement on MRI, indicative of high-grade glioma. FET-PET can therefore be used to locate the most malignant areas of contrast-enhancing gliomas, thereby impacting consequent management.

OBJECTIVE MRI is gold standard for the diagnosis, surgery and radiation therapy of patients with high-grade glioma. Amino acid PET is useful in gliomas without contrast enhancement in MRI but it is unknown whether PET better identifies high-grade foci than T1-sequence with contrast enhancement or improve definition of high grade glioma infiltration related to T2/Flair images. METHODS More than 400 biopsy specimens from twenty-three patients with suspected high-grade glioma were examined in this prospective study. Patients meeting the inclusion criteria were referred for hybrid 18F-FET-PET-MRI before stereotactic biopsy. Biopsies were planned based on early FET-PET acquisition 5-15 minutes post injection and MRI. The following biopsy sites were determined in each case: (i) site of contrast enhancement and increased FET uptake; (ii) contrast enhancement but no increase in FET uptake; (iii) increased FET uptake but without contrast enhancement; and (iv) peripheral areas hyperintense in T2 FLAIR without increased FET uptake and contrast enhancement. RESULTS In 35% cases, the biopsy result was changed to a higher tumor grade after the inclusion of FET-positive sites. In all cases, high FET uptake was visualized and confirmed outside areas of contrast enhancement on MRI, indicative of high-grade glioma. Results from biopsies based on the FLAIR sequences corresponded to neoplastic lesions in 13 cases (57%), most often with a lower grade than in areas of high FET uptake. CONCLUSIONS FET-PET can be used to locate the most malignant areas of contrast-enhancing gliomas and impact the biopsy results. Surgery or radiotherapy planned solely on MRI images may miss parts of tumor presenting highest malignancy. Brain areas hyperintense in T2 FLAIR without increased amino acid uptake are not specific for malignancy in high grade gliomas.