Focal brainstem glioma
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Focal brainstem gliomas are a relatively uncommon type of brainstem glioma, which carry a more favorable prognosis compared to the more common diffuse brainstem glioma. The name is a reflection of the imaging findings, which demonstrate a sharply demarcated mass with relatively frequent enhancement on MRI.
The majority are low grade (60%) with most tumors being pilocytic astrocytomas. Gangliogliomas and oligodendrogliomas also occasionally found. Higher grade tumors (40%) are usually fibrillary astrocytoma or GBM.
The histology of focal brainstem gliomas is variable and may be both of low-grade (accounting for the much better prognosis) or high-grade.
Distinguishing between high-grade and low-grade focal brainstem gliomas is clearly important but difficult, and biopsy potentially carries severe morbidity. Diffusion tensor imaging (DTI) and tractography can help by delineating relationship of tracts with respect to the mass. If tract invasion is demonstrated, this suggests a more infiltrating (thus higher grade and poorer prognosis) histology.
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