April 30, 2011

Anaplastic Astrocytoma

Axial T2W (fig. 1) and T1W post contrast (fig. 2) images of the brain demonstrate a large ill-defined mass (arrows) centered in the right insula with extension to the frontal and temporal lobes. The mass shows a heterogeneous high T2 signal intensity, cystic areas (arrowheads), mass effect and minimal enhancement.

Facts: WHO grading system for primary astrocytic tumor and imaging features
  • Grade I = circumscribed glioma including pilocytic astrocytoma -- no mass effect, no enhancement
  • Grade II = diffuse astrocytoma (cytological atypia alone) -- mass effect, no enhancement
  • Grade III = anaplastic astrocytoma (anaplasia and mitotic activity) -- complex enhancement
  • Grade IV = glioblastoma (also show microvascular proliferation) -- necrosis (ring enhancement)
  • Imaging grading is imprecise but can be used as a preliminary assessment
  • Grading is not applicable to pediatric patients or special astrocytomas
  • Low grade gliomas usually hypodense on CT, hypointense on T1WI and hyperintense on T2WI. High T2 signal intensity commonly extends beyond the tumor volume. Most do not enhance.
  • Anaplastic gliomas may or may not enhance. Calcifications and cysts occur in 10-20%.
  • Glioblastomas usually enhance on the rim, representing cellular tumor but tumor cells often extend beyond 1.5 cm of the enhanced ring. Nonenhancing center may represent necrosis or associated cyst.
  • On imaging, factors affecting prognosis are location (eloquent vs. non-eloquent) and tumor size
Our case: anaplastic astrocytoma.

Greenburg MS. Handbook of neurosurgery, 7th edition, 2010.

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