Imaging characteristics of oligodendrogliomas that predict grade

Abstract

Background and purpose: Oligodendrogliomas are tumors that have variable WHO grades depending on anaplasia and astrocytic components and their treatment may differ accordingly. Our aim was to retrospectively evaluate imaging features of oligodendrogliomas that predict tumor grade.

Materials and methods: The imaging studies of 75 patients with oligodendrogliomas were retrospectively reviewed and compared with the histologic grade. The presence and degree of enhancement and calcification were evaluated subjectively. rCBV and ADC maps were measured. Logistic linear regression models were used to determine the relationship between imaging factors and tumor grade.

Results: Thirty of 75 (40%) tumors enhanced, including 9 of 46 (19.6%) grade II and 21 of 29 (72.4%) grade III tumors (P < .001). Grade III tumors showed lower ADC values compared with grade II tumors (odds ratio of a tumor being grade III rather than grade II = 0.07; 95% CI, 0.02-0.25; P = .001). An optimal ADC cutoff of 925 10(-6) mm(2)/s was established, which yielded a specificity of 89.1%, sensitivity of 62.1%, and accuracy of 78.7%. There was no statistically significant association between tumor grade and the presence of calcification and perfusion values. Multivariable prediction rules were applied for ADC < 925 10(-6) mm(2)/s, the presence of enhancement, and the presence of calcification. If either ADC < 925 10(-6) mm(2)/s or enhancement was present, it yielded 93.1% sensitivity, 73.9% specificity, and 81.3% accuracy. The most accurate (82.2%) predictive rule was seen when either ADC < 925 10(-6) mm(2)/s or enhancement and calcification were present.

Conclusions: Models based on contrast enhancement, calcification, and ADC values can assist in predicting the grade of oligodendrogliomas and help direct biopsy sites, raise suspicion of sampling error, and predict prognosis.

Fig 1.

Grade II oligodendroglioma. A, Axial T2-weighted fast SE image shows a high-signal-intensity mass in left frontal lobe. B, Axial contrast-enhanced T1-weighted image shows no postcontrast enhancement within the left frontal lobe mass. C, Axial automated postprocessed ADC map yields a minimal ADC value of 946 × 10⁻⁶ mm²/s, above the 925 × 10⁻⁶ mm²/s threshold.

Fig 2.

Grade III oligodendroglioma. A, Axial T2-weighted fast SE image shows a high-signal-intensity mass in left medial frontal and parietal lobes. B, Axial contrast-enhanced T1-weighted image shows minimal nodular post–contrast enhancement within the medial margin of the mass. C, Axial automated postprocessed ADC map shows low signal intensity along the posterior margin. D, As stated in “Materials and Methods,” 4 ROIs are placed in the areas visually assessed as the lowest in signal intensity on the ADC map. In this case, of the 4 ROIs, the lowest ADC value is 762 × 10⁻⁶ mm²/s, which was recorded for this grade III oligodendroglioma, below the 925 × 10⁻⁶ mm²/s threshold.