Diagnosis and Imaging of DIPG
The understanding of brainstem tumors, including diffuse infiltrating pontine glioma (DIPG), has advanced considerably over the last few decades largely as a result of advances in imaging technology. Nevertheless, the understanding of brainstem tumors by imaging has always been, and continues to be, limited by the lack of histopathology (microscopic evaluation of tumor tissue) correlating to the imaging characteristics. This is primarily related to the risk involved to the patient through the biopsy of these tumors accompanied by the questionable direct therapeutic benefits for the child.
The development of Magnetic Resonance Imaging (MRI) has significantly improved our understanding of these tumors. MRI allows improved visualization and characterization of brainstem tumors in comparison to Computed Tomography (CT). MRI provides superior imaging of the posterior fossa of the brain in comparison to CT, which is limited secondary to artifacts related to the thick bones of the skull base. Furthermore, in comparison to CT, MRI has superior soft tissue contrast resolution, which aids in characterization of these tumors. The recent development of advanced imaging techniques including magnetic resonance spectroscopy and magnetic resonance perfusion imaging will continue to improve our understanding of these tumors.
Role of Biopsy
Historically, biopsies were done when tumors were considered not typical, were focal, or occurred in much younger or older patients. In recent years, multiple studies have reported that biopsies can be safely done.1,2 In the largest series, from Europe, among 130 patients who were biopsied only 3.9 % had some transient worsening of symptoms and more than 90% of patients were discharged from hospital in less than a week.2
Whether biopsies should be routinely done remains controversial. Material from diagnosis can provide important biological information that may delineate prognosis or help direct the type of therapy to be used.
Pathologists grade a tumor based on its features. The characteristics that pathologists examine include cell growth, cell death, invasion of surrounding normal cells, and the architecture of the tumor itself—this refers to how mature or immature the cells look, among other factors.
Pathologists grade brainstem tumors on a 1 to 4 scale. The lower numbers generally indicate less-aggressive tumors, including pilocytic astrocytomas. The lowest grade consistent with a DIPG is a grade 2 tumor, but many DIPG tumors will be grade 3 or 4 (the most-aggressive, fastest-growing grades).
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