MRI-Based Score to Recognize Thalamic Glioma Grade in Children: Morphology, Diffusion, and Arterial-Spin-Labeling Perfusion.

Purpose: Thalamic gliomas are found predominantly in children and can be classified into two main types with different prognoses and management: diffuse midline glioma (DMG) H3K27-altered and low-grade glioma (LGG). Our aim was to find imaging features distinguishing these tumors and to develop a diagnostic score.

Patients And Methods: A retrospective study spanning September 1999 to May 2021 involved pediatric patients with thalamic gliomas, categorized into H3K27-altered DMG and LGG groups. Preoperative imaging, including morphology, diffusion, and arterial-spin-labeling perfusion, was reviewed blindly and compared between the two groups. A diagnostic score was formulated based on significant findings. Results were validated using an internal and external validation cohort.

Results: Sixty-six patients were included (median age, 9 years; interquartile range [IQR] [5-13]; 38 girls) with 37 DMG H3K27-altered and 29 LGG. DMG H3K27-altered tumors exhibited larger volumes (median 64 cc, IQR [36-88] vs 26 cc, IQR [15-37], p < 0.001), greater heterogeneity in T2-weighted signal and enhancement (62% [22/37] vs 31% [9/29], p = 0.04, and 97% [32/33] vs 56% [15/27], p = 0.0008, respectively), lower minimum relative apparent diffusion coefficient (ADC) (0.92 (IQR [0.76-1.23]) vs 1.55 (IQR [1.40-1.72]), p < 0.001), and higher relative maximum cerebral blood flow (CBF) levels (2.08 (IQR [1.48-3.05]) vs 0.84 (IQR [0.45-1]), p < 0.001). A diagnostic score integrating tumor diameter, solid content predominance, relative ADC, and relative CBF achieved 100% sensitivity and specificity in distinguishing DMG H3K27-altered tumors from LGG (full score available for 36 patients), with good results in external and internal validation cohorts (12 patients).

Conclusion: The morphological, diffusion, and arterial spin labeling imaging characteristics of pediatric thalamic tumors enable excellent differentiation of DMG H3K27-altered and LGG.