Bilateral Thalamic Diffuse Midline Glioma, H3K27M-Altered, in a 3-Year-Old Boy

Area of Science:

• Pediatric neuro-oncology
• Neuro-oncology
• Pediatric pathology

Background:

• Diffuse midline glioma, H3 K27-altered, is a rare and aggressive pediatric brain tumor.
• It often occurs in the thalamus and brainstem, but can present atypically outside the brainstem.
• Imaging may not show typical malignant features, leading to diagnostic challenges.

Purpose of the Study:

• To report a case of diffuse midline glioma, H3 K27-altered, presenting as bilateral thalamic lesions in a pediatric patient.
• To highlight the importance of considering this diagnosis even when imaging findings are non-specific.
• To emphasize the role of early biopsy in preventing diagnostic delays.

Main Methods:

• Case report of a 3-year-old boy with progressive ocular misalignment and left-sided weakness.
• Magnetic resonance imaging (MRI) revealed symmetric bilateral thalamic T2/FLAIR hyperintense lesions.
• Cerebrospinal fluid (CSF) and metabolic investigations were performed.
• Surgical resection of the dominant lesion followed by histopathological analysis and immunostaining (H3K27me3, H3K27M).

Main Results:

• Histopathology confirmed an infiltrative high-grade astrocytic tumor with loss of H3K27me3 and positive H3K27M immunostaining, classifying it as diffuse midline glioma, H3 K27-altered (WHO grade IV).
• Initial imaging findings were suspicious for inflammatory or metabolic disease, delaying definitive diagnosis.
• The patient received radiochemotherapy postoperatively.

Conclusions:

• Bilateral thalamic lesions in children can represent diffuse midline glioma, H3 K27-altered, even without typical malignant imaging features.
• Early biopsy is crucial for unexplained bilateral thalamic lesions to ensure timely diagnosis and appropriate oncologic management.
• This case underscores the need for a high index of suspicion for pediatric brain tumors presenting with atypical imaging characteristics.