The pathology of the central nervous system is an intimidating area for pathologists. In part this is because we have virtually no role in the gross examination, just processing shreds of white pulp on gauze, and in part because of the feeling that “it could be anything at all,” including a long list of exotic zebras that look just like the common things except behave completely differently. The fact that we are often asked to make our diagnoses on frozen section does not help matters. However, even in the brain, the list of likely diagnoses is still reasonably short if you have three pieces of key information: the age of the patient and the location and radiographic appearance of the tumor. Table 26.1 lists differential diagnoses that should at least put you in the right ballpark. A strategy often proposed is to start by asking if your “lesion” could be normal tissue (i.e., the surgeon has missed). To answer this question you have to know a little normal histology, which is reviewed below. Second, you should ask if your lesion is neoplastic or nonneoplastic. The nonneoplastic lesion that many pathologists worry most about is the demyelinating lesion, which can look like a tumor by radiology. Abundant foamy macrophages, and an absence of obvious tumor cells, should make you think of a possible demyelinating lesion. Gliosis, a reactive proliferation of astrocytes, can also simulate a glioma histologically (see next section). However, once you have decided you have a neoplasm, the real work begins.
KeywordsPituitary Adenoma Glioblastoma Multiforme Pilocytic Astrocytoma Microvascular Proliferation Central Neurocytoma
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