Genetically Defined Oligodendroglioma Is Characterized by Indistinct Tumor Borders at MRI

Abstract

Background and purpose: In 2016, the World Health Organization revised the brain tumor classification, making IDH mutation and 1p/19q codeletion the defining features of oligodendroglioma. To determine whether imaging characteristics previously associated with oligodendroglial tumors are still applicable, we evaluated the MR imaging features of genetically defined oligodendrogliomas.

Materials and methods: One hundred forty-eight adult patients with untreated World Health Organization grade II and III infiltrating gliomas with histologic oligodendroglial morphology, known 1p/19q status, and at least 1 preoperative MR imaging were retrospectively identified. The association of 1p/19q codeletion with tumor imaging characteristics and ADC values was evaluated.

Results: Ninety of 148 (61%) patients had 1p/19q codeleted tumors, corresponding to genetically defined oligodendroglioma, and 58/148 (39%) did not show 1p/19q codeletion, corresponding to astrocytic tumors. Eighty-three of 90 (92%) genetically defined oligodendrogliomas had noncircumscribed borders, compared with 26/58 (45%) non-1p/19q codeleted tumors with at least partial histologic oligodendroglial morphology (P < .0001). Eighty-nine of 90 (99%) oligodendrogliomas were heterogeneous on T1- and/or T2-weighted imaging. In patients with available ADC values, a lower mean ADC value predicted 1p/19q codeletion (P = .0005).

Conclusions: Imaging characteristics of World Health Organization 2016 genetically defined oligodendrogliomas differ from the previously considered characteristics of morphologically defined oligodendrogliomas. We found that genetically defined oligodendrogliomas were commonly poorly circumscribed and were almost always heterogeneous in signal intensity.

Fig 1.

Examples of circumscribed (A and D), partially circumscribed (B and E), and noncircumscribed (C and F) tumor borders on axial T1-weighted (upper row) and T2-weighted (lower row) MR images.

Fig 2.

Examples of tumor classifications are as follows: circumscribed, with sharp smooth borders (A); circumscribed, with sharp borders, but not smooth due to the extent of concave inward borders (B); circumscribed with sharp borders on T2-weighted image (C) but not on T1-weighted image (D); partially circumscribed, with indistinct borders, but not smooth due to the extent of concave inward borders (E); and circumscribed, with predominantly sharp borders, but not smooth due to the extent of concave inward borders (F). All images are T2-weighted, except D as indicated.

Fig 3.

MR images of a prototypical genetically defined (1p/19q codeleted) oligodendroglioma (upper row) and of an astrocytoma with microscopic oligodendroglial features but no 1p/19q codeletion (lower row). Axial T2-weighted (A and D), T1-weighted postcontrast (B and E), and ADC (C and F) images. Genetic oligodendrogliomas tend to be located in the frontal or parietal lobe and lack circumscription, are heterogeneous, and have lower ADC values. The mean ADC value of the tumor in C is 1.26 mm²/s. Astrocytomas in this cohort with microscopic oligodendroglial features tend to be located in the temporal or insular lobes, are frequently well circumscribed, and have higher ADC values. The mean ADC value of the tumor shown in F is 1.92 mm²/s.

Fig 4.

Boxplot demonstrating the distribution of mean ADC values by the WHO 2016 classification as oligodendroglioma or astrocytoma.