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James G. Smirniotopoulos, M.D. Professor of Radiology and Neurology Chairman, Department of Radiology and Nuclear Medicine Uniformed Services University of the Health Sciences Bethesda, MD USA |
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WHO (World Health Organization) forever changed the way we look at brain
neoplasms when their landmark classification was published in 1993.
In 2000, a further refinement of this classification system was
published. The WHO classification stratifies neoplasms by their
overall biologic potential. Lower grade tumors have the best
prognosis. The category of Grade 1 is reserved for neoplasms that
have a stable histology. Tumors that appear histologically "benign",
yet are known to progressively transform over time, are not included under
Grade 1 lesions.
The WHO classification also recognized and defined some new specific subtypes of astrocytoma. These subtypes were also assigned a grade. One of the most confusing issues in radiologic-pathologic correlation is the complex relationship between enhancement and tumor grading: Most malignant tumors enhance; yet, some of the most benign neoplasms also enhance. The key here is to understand and to recognize that there is a constellation of imaging and demographic features that are seen in the low-grade enhancing neoplasms. When these parameters are understood, enhancement in a low-grade tumor is not only acceptable - it is expected. Listed below, in table format, are the major correlations between astrocytomas, their WHO grade, the nature of being localized or infiltrating, and the presence of contrast enhancement on CT and MR. |
| Circumscribed Astrocytoma | Diffuse Astrocytoma | |
| Stable Histology (WHO Grade) |
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| Unstable Histology
(Grade) |
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| Circumscribed Astrocytoma | Diffuse Astrocytoma | |
| No Enhancement | . |
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| Variable Enhancement |
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| Routine Enhancement |
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