Imaging of Diffuse Intrinsic Pontine Gliomas in Children

Diffuse intrinsic pontine gliomas are diagnosed by their clinical signs and symptoms on presentation and their appearance on imaging. Since the publication of the Children’s Cancer Group (CCG) report in 1993 (32) that outlined the typical presentation and radiographic appearance of these brainstem tumors, most believe that these findings are diagnostic and a biopsy is unnecessary. If, however, the clinical or radiological presentation is not typical, or if brainstem encephalitis or an inflammatory process of the pons cannot be ruled out, many would argue for a stereotactic biopsy before initiating radiation therapy and chemotherapy.

CT Scan

A CT scan is not the ideal study for the imaging of diffuse tumors. It may suggest a tumor if there is a hypodense and expanded pons.

Axial CT scan of a diffuse brainstem glioma: Note very hypodense central portion of tumor with surrounding hypodensity spreading into the cerebellum. This spreading hypodensity commonly contains tumor cells.

Axial CT scan with constrast enhancement of a diffuse intrinsic pontine glioma: Shown is the same diffuse intrinsic pontine glioma with contrast enhancement. Note rim enhancement with central hypodense zone of poor perfusion. Necrosis is commonly found in this region.

MRI

• Diffuse intrinsic pontine gliomas infiltrate widely: Diffuse intrinsic pontine gliomas are typically diagnosed by their clinical presentation and imaging. MRI shows infiltrative expansion of the pons that is typically hypointense on T1-weighted images, hyperintense on T2-weighted and FLAIR images, and has no significant dorsal exophytic component. Involvement of adjacent levels of brainstem and/or cerebellum is common.
• Diffuse intrinsic pontine gliomas can encase basilar artery: Envelopment of the basilar artery is common.
• Gadolinium enhancement is uncommon and has no prognostic significance: Enhancement with gadolinium is variable, with no enhancement being common (95). Enhancement, if present, is usually patchy, without known prognostic significance.
• Neuraxis dissemination common during progression: During progression, neuraxis dissemination can be seen in more than 50% of patients on MRI (31).
• MRS is helpful in differential diagnosis: Increased Cho/NAA and Cho/Cre ratios are helpful in differentiating diffuse intrinsic pontine gliomas from brainstem encephalitis, demyelination, and other inflammatory processes when clinical and MRI presentations are atypical (96, 97). However, the differentiating power of MRS is limited in NF1-associated diffuse intrinsic pontine gliomas (97).

Diffuse intrinsic pontine glioma: Shown is a T1-weighted sagittal image.

Diffuse intrinsic pontine glioma: Shown is a T2-weighted sagittal image.

Contrast-enhanced T1-weighted image of diffuse intrinsic pontine glioma: This gadolinium- enhanced T1-weighted sagittal image shows an unusual amount of enhancement, as these tumors typically have heterogeneous or no enhancement.

Diffuse intrinsic pontine glioma: This T2-weighted axial image shows envelopment of the basilar artery.