The butterfly lesion – learn how to recognize a glioblastoma multiforme (GBM) on MRI.
We recently published a post about ring-enhancing lesions, using the mnemonic MAGICL DR to remember the differential diagnosis.
One important ring enhancing lesion on brain MRI is a glioblastoma multiforme, or GBM – an aggressive type of brain tumor. A GBM is a high grade primary brain tumor. It develops from atrocytes, and is therefore called a stage IV astrocytoma.
Glioblastomas have a tendency to spread across the corpus callosum, creating a bihemispheric lesion, sometimes described as resembling a butterfly.
GBM’s represent about 15% of all intracranial tumors, and are the most common adult intra-axial tumor, which refers to tumors arising from within the brain. (Reminder, the most common extra-axial tumor is a meningioma).
The inner core of a GBM represents necrotic tissue. The outer, enhancing ring is made of hyper-vascularized tissue. GBM’s spread quickly, and are aggressive brain tumors with poor long term prognosis.
GBM’s often have a shaggy, contrast enhancing ring surrounding an area of central necrosis. There may be edema around the lesion. They may cross the corpus callosum, or extend into the brainstem.