Diffusion MRI in the early diagnosis of malignant glioma

A subset of patients with malignant glioma comes to medical attention before their masses show rim enhancement and central necrosis. Tumors in those cases are frequently located in eloquent areas of the brain. Tissue diagnosis is limited to stereotactic biopsy providing limited material for accurate grading. We conducted this study to determine whether imaging characteristics of early stages of malignant gliomas could aid in timely definitive diagnosis.

We retrospectively analyzed patients with newly diagnosed malignant glioma seen at the Yale Brain Tumor Center between 2002 and 2005. Patients with typical radiographic presentation were excluded.

Of 89 patients, eight meeting the inclusion criteria were identified. In five patients, patchy or small nodular enhancing lesions without central necrosis were present within the tumor mass. Diffusion-weighted imaging (DWI) showed areas of increased signal intensity in all cases. Apparent diffusion coefficient maps (ADC) revealed low-signal intensity in corresponding areas. At the time of imaging, biopsy was performed in seven patients but diagnosis of malignant glioma could only be established prior to further tumor growth in four cases.

The diagnosis in the early stages of malignant glioma can be challenging in a subset of cases. Information obtained through DWI should be incorporated in the clinical decision-making process. Mass lesions displaying decreased water diffusion indicating high cellularity, are suggestive of a high-grade glioma. Biopsies are recommended. However, even when biopsies are inconclusive, a strong suspicion of malignant glioma should be considered.