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Is there imaging characteristics for histologic grade in oligodendroglioma?

JVIM 2022

Bénédicte Amphimaque, Alexane Durand, Anna Oevermann, Beatriz Vidondo, Daniela Schweizer

Background
Oligodendroglioma (OG), a type of glioma, constitutes 22% of primary brain tumors in dogs. Its grade, based on histology, reflects biological behavior, with low-grade (II) and high-grade (III) determined by the presence of necrosis and microvascular proliferation. This study aimed to explore whether magnetic resonance imaging (MRI) features can differentiate between OG grades, providing a noninvasive grading tool to complement or substitute histological assessment.

Methods
This retrospective study included 32 dogs with histologically confirmed OGs and available MRI data. MRI studies were evaluated for features like contrast enhancement (CE), necrosis, cystic structures, and signal intensity. Histological and MRI findings were compared using statistical methods to identify associations with OG grade.

Results
Tumor Grading: Histologically, 75% were high-grade (OG III) and 25% low-grade (OG II).

MRI Features:
-Contrast Enhancement: Moderate-to-marked CE was present in all OG III but absent in OG II. A CE ring pattern occurred in 75% of OG III cases and none of OG II cases.
-Other Indicators: Tumor heterogeneity, necrosis, cystic structures, and gradient-recalled echo (GRE) signal voids were strongly associated with OG III.
-Signal Intensity: OG III exhibited heterogeneous signals, while OG II showed homogeneous patterns.


Predictive Accuracy: Moderate-to-marked CE and ring enhancement patterns were highly specific for OG III.

Diffusion-Weighted Imaging (DWI): No differences in apparent diffusion coefficient (ADC) values were observed between grades.

Limitations
The uneven distribution of high-grade versus low-grade cases (24:8) may limit the generalizability of the findings. Additionally, the study lacked quantitative ADC analysis, and not all MRI sequences were available for every case.

Conclusions
MRI features, particularly moderate-to-marked CE and a CE ring pattern, are reliable indicators of high-grade OG in dogs, aligning with histological findings. These results support the use of MRI for noninvasive tumor grading and guide biopsy targeting for precise histological assessment. Future research is needed to refine MRI-based prognostic models and compare these findings with other glioma types.

Transverse postcontrast T1-weighted magnetic resonance image of a homogeneous, nonenhancing canine low-grade oligodendroglioma (OG) (A) with corresponding histology (B and C) and of a strongly ring-enhancing high-grade OG (D) with corresponding histology (E and F). (A) shows the lack of contrast enhancement (CE) in low-grade OG. In histology, low magnification of the same low-grade OG (B) shows a dense population of neoplastic cells infiltrating the neuropil and the subarachnoid space. Necrosis is absent, while a mucinous lake (asterisk) is present in the center of the mass. High magnification shows layers of densely packed cells with scant cytoplasm and hyperchromatic nuclei, embedded in abundant mucinous background and supported by delicate “chicken wire” capillaries. Note the absence of necrosis and microvascular proliferation. Marked peripheral ring of CE visible in a high-grade OG (D) and correlated with central necrosis (E) and presence of peripheral microvascular proliferation with hypertrophic glomeruloid capillaries (F) in histology

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