Low-Grade Astrocytoma

Astrocytomas are the most common primary, solitary, supratentorial brain lesion in adults (all these qualifiers are meant to hide the fact that brain lesions are most commonly metastases). The World Health Organization classifies them into 4 grades.

• Grade I (Circumscribed astrocytomas): Relatively benign biology and indolent clinical course. Include pilocytic astrocytoma, pleomorphic xanthoastrocytoma, subependymal giant cell astrocytoma.
• Grade II (Diffuse astrocytomas): Shown above. Cell types include fibrillary, gemistocytic, and protoplasmic astrocytomas. 1/3 occur in the frontal lobe and 1.3 occur in the temporal lobe. Cystic change and calcification may occur. Less likely to show enhancement.
• Grade III (Anaplastic astrocytomas): Usually evolve from lower grade astrocytomas. Ill-defined borders and extensive surrounding edema. More likely to show enhancement. Should not have cystic change.
• Grade IV (Glioblastoma multiforme): Most common variety of astrocytoma. Occur de novo in the elderly and are thought to arise from lower grades in younger patients. Characterized by necrosis.

References

Cha S. Update on brain tumor imaging: from anatomy to physiology. AJNR Am J Neuroradiol. 2006 Mar;27(3):475-87.