Specific Imaging Findings

MRI is the imaging modality of choice for low-grade diffuse astrocytomas and the extent of the lesion is best defined on FLAIR images. They are typically homogenous intra-axial masses with the epicenter within the white matter and minimal to mild associated mass effect. They can be found in all parts of the supratentorial brain, more commonly in the insula. The tumors are usually well-delineated with high T2 signal and iso- to hypointense on T1WI, infiltrating and expanding the underlying brain; the margins are in some cases poorly defined. Diffuse low-grade astrocytomas are typically bright on ADC maps, consistent with increased diffusivity, and usually do not enhance with contrast. On perfusion studies they show relatively low cerebral blood volume, on average only slightly higher compared to the normal brain. MR spectroscopy usually shows decreased NAA levels with slightly elevated choline and without lactate. Low-grade diffuse astrocytomas are typically slightly hypodense to normal brain on CT.

Pertinent Clinical Information

The patients are typically young adults presenting with seizures without other symptoms, or even asymptomatic with the lesion found incidentally on imaging studies. These tumors undergo malignant transformation portended by clinical decline and radiographic progression. There is no consensus on the best management of adults with presumed low-grade glioma; it usually includes surgical resection, which may be followed by chemotherapy. Alternatively, the tumors can be followed with imaging after the initial biopsy, as patients may prefer to defer surgery until there is progression or a change in quality of life.