Imaging is the primary diagnostic tool for DIPG. CT is often the first exam obtained, as it can be quickly performed without sedation/anesthesia. It will usually show a low-density expansion of the pons with flattening of the fourth ventricle. However, some lesions are extremely subtle on CT, and MR imaging is the preferred diagnostic modality. MR typically shows a diffuse expansion of the brainstem/pons by a tumor that is poorly defined but abnormally bright in signal on T2-weighted images and abnormally dark on T1-weighted images. Contrast enhancement is seen in the minority of DIPG, and when present is typically mild. There may be some indication of necrosis, and the basilar artery is commonly engulfed by tumor. Hemorrhage and calcification are uncommon.
MR spectroscopy may be helpful in distinguishing tumor from brainstem encephalitis, and may have a role inguidingbiopsy or evaluating response to therapy. PET scans have been used in some cases to guide biopsy. Surveillance MR imaging can be used to monitor response to therapy and progression of disease, however clinical assessment is usually much more reliable.