Anaplastic Astrocytoma (AA)
|This article has been reviewed by the NeuroWiki Editorial Board|
|Anaplastic Astrocytoma (AA)|
Axial FLAIR MRI of left insular AA
|Cell of origin||Glial Cell|
|Treatment||Surgery,Radiation and Chemotherapy|
AA is an astrocytic neoplasm, typically affecting adults in middle age, biologically characterized by a marked proliferative potential. AA corresponds to WHO Grade III astrocytoma. They have an intrinsic tendency for malignant progression to GBM.
Mean age of diagnosis is approximately 41 years. There is a male predominance (1.8:1).
AA has a preference for the cerebral hemispheres.
Patients may present with seizure or signs and symptoms attributable to mass effect or brain invasion.
On MRI, AA is usually hypointense on T1-weighted imaging and hyperintense on FLAIR and T2-weighted imaging. These lesions usually demonstrate partial enhancement, with associated brain edema and evidence of mass effect. Notably, some 30% of non enhancing astrocytomas will have histologic features consistent with AA.
AA is often difficult to distinguish grossly from Low Grade Glioma (LGG). The tumor-brain interface may be more readily discerned that the tumor-brain interface in LGG. As in LGG, there is usually enlargement or distortion, rather than overt destruction, of surrounding anatomical structures. Macrocysts are uncommon.
AA is composed of diffusely infiltrating neoplastic astrocytes with increased cellularity, nuclear atypia and marked mitotic activity. Microvascular proliferation and necrosis are absent. GFAP, vimentin, and S-100 are diffusely expressed.
Growth fraction, as determined by the Ki-67/MIB-1 index, is usually 5-10%.
TP53 mutations are common in these lesions. Deletion of p16(Ink4A) is found in about 30% of AA, as are alterations in RB (25%) and p19 (15%). CDK4 amplification occurs in about 10% of these lesions. LOH on chromosomes 10q, 19q, and 22q are also common. EGFR amplification is rare.
Mean survival time following surgical intervention is 3 years. Progression to GBM occurs with a mean interval time of 2 years. Young age, high Karnofsky score, and gross total tumor resection are considered predictive of increased survival.