If Abnormal, is the Abnormality Specific or Non-specific?
There are certain pathological changes - abnormal but very common, frequently associated with age or derived from old subclinical injuries - that usually pose no clinical significance. These should not delay the investigation too much and include the following: thickening of the leptomeninges, atherosclerosis, fibrosis or hyalinization of blood vessels, mineral deposits in various parts of the nervous system, lipofus-cin in neurons, corpora amylacea, mild gliosis without other specific pathological changes, acute (usually operative) and even old (remote) hemorrhages, necrosis without other specific findings, and mild inflammatory changes in the absence of other specific changes.
Among these may be considered the differential diagnosis of gliosis vs low-grade glioma. This is the most frequent problem that neophytes expect to encounter according to their grapevine! Actually, however, for the usual neophyte the boundary lies well up in the scale of hypercellularity simply because the true neophyte has had essentially no experience with the normal, much less the abnormal.
Gliosis is a scar in the CNS analogous to fibrosis in other organs. It only tells us that the tissue is abnormal because something has happened there, or near there, in the remote past and has been repaired. The scar remains but the cause of the scar is no longer present. An old gliosis consists of abundant astrocytic fibers and few cell bodies or nuclei. More recent gliosis contains more cell bodies with plump cytoplasm ("gemistocytes") and less prominent fibers. Such recent or progressive gliosis is difficult to distinguish from a low-grade astrocytoma.
This is a problem on which even expert neuropathologists disagree frequently, especially when the biopsy specimen is either insufficient in quantity or misses the target. There is no single easy criterion to separate the two conditions. Increased density of cells is not always diagnostic of a glioma, since atrophic white matter can be more hypercellular than even a real low-grade glioma. Immune stains for glial fibrillary acidic protein (GFAP) usually show
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