Oligodendrogliomas

To study the pattern of contrast enhancement in MR and CT of oligodendrogliomas and to compare this with other imaging findings and with histopathological grading criteria.

20 patients with oligodendrogliomas (12 low-grade WHO II and 8 anaplastic WHO III) were reviewed. 20 complete MR investigations, 20 non-enhanced CT studies and 16 CTs after contrast enhancement were estimated blindly without knowledge of the tumour histological grades.

All anaplastic oligodendrogliomas showed tumour contrast enhancement on MR and CT images. Also in 6/12 low-grade oligodendrogliomas the contrast was enhanced on MR imaging. In 5 of these, tumour calcifications were detected by CT. The remaining 6/12 WHO grade II cases showed no significant MR contrast enhancement. Of the oligodendrogliomas grade II, CT showed contrast uptake in 3 cases and no enhancement in 6, while in 3 cases postcontrast CT was not available. A comparison of contrast enhancement with tumour grade resulted in a p-value of 0.042 for MR and of 0.011 for CT. A combined statistical test of tumour grade and calcifications detected by CT compared with MR contrast enhancement showed a significant correlation (p=0.014).

These data demonstrated that a clear grading of oligodendrogliomas based on the image criterion MR contrast enhancement was not possible. We suppose that, besides tumour neovascularisation, additional factors such as calcifications may disturb the blood-brain barrier.