MR imaging in cerebral gliomas analysis of tumour tissue components

The aim of this investigation was to assess the capacity of MR imaging to identify the tumour components of cerebral gliomas and thus to grade and delineate these tumours. A comparative analysis between MR examinations and histopathologic whole-brain sections was performed in 5 brain specimens from patients with malignant glial tumours. All cases were examined with MR imaging in vitro. In 2 cases a close comparison with the MR examination in vivo was also possible. The homogeneous hypercellular tumour core was not an isolated entity with typical signal characteristics in any sequence used. However, the tumour core was better observed in T2WI than in T1WI or PDWI, its signal characteristics both in vitro and in vivo being more hypointense than the peritumoural oedema. The use of image subtraction and T2 maps in combination with T2WI increased our capacity to correctly distinguish the most malignant part, compared with using each of these methods separately. In all cases, benign-looking tumour cells were found in the most peripheral aspects of the peritumoural oedema. These cells were not separately identified by any MR sequence or MR imaging method used. In 4 of the 5 cases of malignant glial tumours, we found isolated tumour cells and even larger tumour cell areas, though consisting of benign-looking cells, in areas that were visualized as normal in all sequences and MR imaging methods used. In all cases the necroses were heterogeneous. This heterogeneity was best reflected in the T2WI. Necroses were the most conspicuous tumour components in cases of malignant glioma and best reflected the underlying heterogeneous histopathology. A comparison between contrast-enhanced CT, Gd-DTPA-enhanced MR imaging and positron emission tomography (PET) with 11C-L-methionine was performed in 14 patients. In all patients except one, the area of increased 11C-L-methionine accumulation on PET, indicating viable tumour tissue, was the same size as, or larger than the extension of the contrast enhancement on both CT and MR. Contrast-enhanced MR and CT gave similar results as regards tumour extension. The increase in signal intensity 5 min post-contrast tended to be greater in the high-grade than in the low-grade tumour group. In order to evaluate the short- and long-term effects of formalin fixation on T1 and T2 of cerebral grey and white matter, MR imaging was also performed in 5 whole-brain specimens from patients with no known brain disease.(ABSTRACT TRUNCATED AT 400 WORDS)