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Anaplastic Astrocytoma


KEY FACTS

Terminology

  • Diffusely infiltrating malignant astrocytoma with anaplasia, marked proliferative potential

Imaging

  • Infiltrating mass that predominately involves white matter with variable enhancement

  • T2 heterogeneously hyperintense

  • Neoplastic cells almost always found beyond areas of abnormal signal intensity

  • May involve and expand overlying cortex

  • Usually no enhancement; focal, nodular, homogeneous, patchy enhancement less common

    • Ring enhancement is suspicious for glioblastoma (GBM)

  • MRS: Increased Cho/Cr ratio, decreased N -acetylaspartate

  • MRP: Elevated maximum regional cerebral blood volume

  • Anaplastic astrocytomas have histologic and imaging characteristics along spectrum between low-grade astrocytoma and GBM

Top Differential Diagnoses

  • Low-grade diffuse astrocytoma

  • GBM

  • Oligodendroglioma

  • Cerebritis

  • Ischemia

Pathology

  • WHO grade III

  • Usually evolves from low-grade (diffuse) astrocytoma (WHO grade II) (75%)

Clinical Issues

  • Most common presentation: Marked clinical deterioration in patient with grade II astrocytoma

  • Occurs at all ages, most common 40-50 years; 1/3 of astrocytomas

  • Prognosis: Median survival: 2-3 years

    • IDH1 (+) and MGMT (+) associated with increased survival

    • IDH1, ATRX wild-type (not mutated) = poor prognosis

Axial graphic shows an infiltrative white matter mass with extension along the corpus callosum, focal hemorrhage
, and local mass effect. White matter extension is typical of anaplastic astrocytoma (AA). They are most commonly located in the cerebral hemispheres.

Axial T2 MR shows a heterogeneously hyperintense mass with local mass effect
in the frontal lobe. AA, WHO grade III, was diagnosed at resection. These high-grade gliomas have a tendency to degenerate into glioblastomas (GBM).

MRS image in a patient with a tectal anaplastic astrocytoma shows a typical malignant tumor spectrum with a high choline peak
and a low N-acetylaspartate peak
.

Coronal FLAIR MR in a 47-year-old man shows a heterogeneously hyperintense mass
centered in the frontal lobe white matter. Anaplastic astrocytomas represent 1/3 of all astrocytomas. Anaplastic astrocytomas are intermediate between low-grade (diffuse) astrocytoma (WHO grade II) and GBM (WHO grade IV).

TERMINOLOGY

Abbreviations

  • Anaplastic astrocytoma (AA)

Synonyms

  • Grade III astrocytoma, malignant astrocytoma, high-grade astrocytoma

Definitions

  • Diffusely infiltrating malignant astrocytoma with focal or diffuse anaplasia and marked proliferative potential

IMAGING

General Features

  • Best diagnostic clue

    • Infiltrating mass that predominately involves white matter (WM) with variable enhancement

  • Location

    • Hemispheric WM

      • –

        Commonly involves frontal and temporal lobes

    • May involve pons, thalamus (pons common in children)

    • Less commonly involves brainstem, spinal cord

  • Size

    • Variable

  • Morphology

    • Ill-defined hemispheric WM mass typical

    • May appear well circumscribed

    • Neoplastic cells almost always found beyond areas of abnormal signal intensity

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