Introduction
The
WHO classification of tumors of the central nervous system (CNS) is a comprehensive system used by pathologists and oncologists to categorize and grade tumors based on their histological and molecular characteristics. This classification is crucial for diagnosing, prognosticating, and planning treatment strategies for patients with CNS tumors.
What is the basis of the WHO classification?
The WHO classification primarily relies on the
histological analysis of the tumor tissue. This involves examining the microscopic features of the tumor cells, such as cell type, cell morphology, and the pattern of cell growth. In recent years, the classification has been updated to include
molecular markers and genetic alterations, which can provide additional prognostic information and guide targeted therapies.
Grade I: These tumors are generally low-grade, slow-growing, and less likely to invade surrounding tissues. Examples include
pilocytic astrocytoma and subependymal giant cell astrocytoma.
Grade II: These tumors are low-grade but have a higher potential for recurrence and slightly more aggressive behavior. Examples include
diffuse astrocytoma and oligodendroglioma.
Grade III: These are high-grade tumors with more aggressive behavior and higher recurrence rates. Examples include anaplastic astrocytoma and anaplastic oligodendroglioma.
Grade IV: These are the most aggressive and malignant tumors, such as
glioblastoma and medulloblastoma.
Gliomas: These tumors arise from glial cells and include astrocytomas, oligodendrogliomas, and ependymomas.
Neuronal and mixed neuronal-glial tumors: These tumors contain both neuronal and glial components, such as gangliogliomas and dysembryoplastic neuroepithelial tumors.
Embryonal tumors: These are highly malignant tumors that occur primarily in children, such as medulloblastomas and atypical teratoid/rhabdoid tumors.
Meningiomas: These tumors arise from the meninges, the protective layers surrounding the brain and spinal cord.
Pituitary tumors: These include pituitary adenomas and craniopharyngiomas.
Other CNS tumors: This category includes a variety of rare tumors, such as hemangioblastomas and primary CNS lymphomas.
What is the role of molecular markers in CNS tumor classification?
In recent updates to the WHO classification, molecular markers have become increasingly important. These markers can provide critical information about the tumor's biology and potential response to treatment. For example, the presence of
IDH mutations in gliomas is associated with a better prognosis. Similarly, 1p/19q co-deletion in oligodendrogliomas indicates a favorable response to chemotherapy and radiation.
How does histological examination support the diagnosis?
Histological examination involves staining the tumor tissue with various dyes and examining the cells under a microscope. Common staining techniques include
Hematoxylin and Eosin (H&E) staining, which highlights the general structure of the tissue. Immunohistochemistry is also used to detect specific proteins within the cells, providing additional diagnostic and prognostic information. For instance, the expression of
GFAP (glial fibrillary acidic protein) can identify astrocytic tumors, while synaptophysin staining can help identify neuronal tumors.
Conclusion
The WHO classification of CNS tumors is a dynamic and evolving system that integrates both histological and molecular features to provide a comprehensive framework for the diagnosis and treatment of CNS tumors. Understanding the histological and molecular basis of this classification is essential for accurately diagnosing and effectively managing CNS tumors.
