Imaging description

Brainstem gliomas are 10–20% of all CNS tumors in the pediatric population, with 80% being diffuse intrinsic pontine gliomas (DIPGs). Because of the risks associated with biopsying DIPGs, currently the diagnosis is based on MRI features alone, with biopsy reserved for atypical cases [1]. Median survival is approximately 9–12 months, and 90% of the patients die before 2 years. Radiotherapy is considered to be the standard treatment modality, with many chemotherapy protocols being tried although there is no treatment currently available that has a significant impact on outcome. Proponents of biopsy diagnosis argue that modern steriotactic methods have decreased risk and obtaining tissue and studying molecular features of these tumors may help facilitate novel treatments. Regardless, MRI remains the main tool in diagnosis and management of these children.

The classic MRI features of DIPG include T1 hypointense and T2 heterogeneously hyperintense, ill-defined lesions occupying more than 50% of the cross-sectional surface area of the pons but not extending outside the brainstem (Fig. 25.1). They tend to grow and extend superiorly and inferiorly with progressive expansion of the brainstem. Exophitic growth is common, particularly anteriorly, engulfing the basilar artery. They might compress the fourth ventricle, but hydrocephalus is rare at presentation. Contrast enhancement is usually absent; when present it’s usually minimal and patchy. While conventional MRI features are helpful in establishing the diagnosis, they cannot predict outcome, with the possible exception of enhancement. Lately, functional MRI methods are used to predict outcome; increased rCBV on susceptibility-weighted perfusion MRI, increased choline/NAA ratio on MR spectroscopy, and enhancement on post-contrast T1-weighted images are associated with shorter mean survival time [2,3].