Neuropathology

Diffusely Infiltrating with No Significant Pattern This type of pattern can be seen in all types of gliomas: gangliogliomas, lymphomas, primitive neuroectodermal tumors (PNETs), germinomas, melanomas, sarcomas and some types of carcinoma. Some show relatively subtle patterns: germinomas can be identified because of the mixture of two distinct cell types: large epithelioid cells and small lymphocytes. Islands of nuclei in a sea of glial fibers are seen in the adult spinal cord (Fig. 3.6a) and are typical of subependymomas (Fig. 3.6b). Lymphoma cells tend to be densely packed around blood vessels, even laminated. Homer Wright pseudorosettes, described below, may be found in PNETs with neuroblastic differentiation but frequently require careful search.

Perineuronal Satellitosis Oligodendrogliomas have a tendency to proliferate close to the cell bodies of neurons in the gray matter, a phenomenon known as "perineuronal satellitosis". Astrocytes and microglia also occur normally and abnormally in a satellite position but oligodendrogliomas seem to be the most common neoplasm to produce this pattern. Two or three glial cells around a neuron are common, indeed normal, but more than that is abnormal. In tumors, there are an increased number of satellite cells, which usually show some nuclear pleo-morphism (Fig. 3.7). Often the presence of a neuron in the center is obscure and one sees only a regular scattering of clumps of tumor cells in the gray matter, suggesting the distribution of neurons previously present. Satellitosis is not specific for a neoplasm, but can be seen in reactions to various non-specific infections and intoxications.

Streams and Bundles Most frequently seen in schwannomas, streams of interlacing bundles of elongated spindle-shaped cells are present in Antoni Type A regions (Fig. 3.8); cut in cross-section, the spindle-shaped nuclei become small and round. Meningiomas, especially of the fibrous variant, can also show this pattern, but

Fig. 3.6. a Islands of nuclei in a sea of glial fibers in a normal adult spinal cord. NP282, H&E. bSimilar islands in a subependymoma. NP171, H&E.
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