Case 1a -

Low Grade Astrocytoma Timothy Smith and Cynthia Welsh

Low grade tumors in adults tend to be associated with presenting seizure or long standing headache more often than high grade tumors, or may be an incidental finding. Tumors in adults tend to be supratentorial, and low grade tumors are no exception. The most common low grade tumors in adults, diffuse (fibrillary) astrocytomas, followed by less common oligodendrogliomas, are infiltrative on MRI scans, bright on T2 and FLAIR sequences, and do not enhance. However, a number of the other low grade gliomas (PXA, ependymoma, JPA and ganglion cell tumors) are distinct from surrounding neural tissue. Low grade tumors other than JPA do not typically enhance or have necrosis. They often have cysts and are generally seen in younger adults. Glial tumors that infiltrate, such as fibrillary astrocytomas and oligodendrogliomas, may track along white matter tracts giving a thickened corpus callosum and/or internal capsule. Intra-operatively, the age, clinical presentation, and fact that the tumor does not enhance should influence you heavily in favor of a low grade process. White matter based lesions tend to be astrocytic. The cortical based ones are often oligodendroglial, DNET, or, particularly if grossly cystic, PXA, ganglioglioma, or even pilocytic. The low grade astrocytoma will often be of low cellularity with the chief histologic differential being reactive gliosis. The astrocytes in a reactive process tend to remain evenly spaced and always have abundant cytoplasm in the acute state (chronically they may shrink down somewhat). The processes are more evenly spaced around the nucleus and more likely to be all long and thin. Neoplastic astrocytes have fewer, short, stubby processes and may "cluster" abnormally. Neoplastic nuclei are large, irregular, and may be "bare" of obvious processes. Occasionally microcysts, calcifications, and/or satellitosis will be present (although less commonly than in oligodendrogliomas). Gliosis Diffuse Astrocytoma History Radiologic findings Loss of grey-white junction Distribution of cells Even Irregular, clusters Bare nuclei No yes Microcysts Rare Common Macrophages Depends on process Rare Other inflammatory cells Depends on process Rare Satellitosis No Yes Cell processes Thin, long, uniform Short, fat, More Rosenthal fibers than cells? Frequent Seldom Calcification No Maybe Vessels Enlarged endothelial Increased numbers cells