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Editorial

Brain Tumors

Updates and Practical Considerations

Ames, Heather M. MD, PhD*; Smith, Michael T. MD

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doi: 10.1097/PCR.0000000000000363
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This issue of the American Journal of Surgical Pathology Reviews and Reports covers neuropathology, but not all of it. Neuropathology is a fascinating specialty, for general pathologists and neuropathologists alike. For nonneuropathologists, the approach to a neuropathology case may be anticipated with some ambivalence or maybe fear. This editorial is cowritten from the perspectives of 2 neuropathologists at different stages of their careers and with different career paths in surgical neuropathology. The first neuropathologist (M.T.S.) has, over many decades, morphed into an experienced surgical pathologist with a generalized academic practice. The second editor (H.M.A.) is a recently boarded neuropathologist with dual roles as an academic neuropathologist and a basic scientist researching the cellular and molecular biology of glioblastoma. The contents of this issue are intended to present clarity, explanation, and education for some of the very important and frequently encountered cases and decision trees in modern surgical neuropathology.

Our first review, for example, covers the history of glioblastoma diagnosis, which is the most commonly encountered primary malignancy in the brain, as guided by the World Health Organization classification system.1 This system represents the most global consensus on glioblastoma diagnosis, since the term “glioblastoma multiforme” was accepted in the early 1930s scrapping the first, less durable, name of “spongioblastoma multiforme,” given by Globus and Strauss in 1925.2 Interestingly, “spongioblast” was a term originally applied to polarized neural progenitors that could give rise to astrocytes, oligodendroglia, ependymal cells, and neurons—now broadly defined as neural stem cells.3,4 The second part of that name, “multiforme,” has now been dropped; however, the molecular diversity of these tumors is proving as complex as their histology. The classification of gliomas, like that of other areas, for example, head and neck tumors, now needs specific molecular testing, which has a recommended decision tree that is currently being transcribed by anticipated guidelines from the College of American Pathologists. These issues along with diagnosis are addressed didactically by Drs Welsh and through a review of example cases by Drs Canbeldek and Ames.

Second, we cover medulloblastoma, the most common high-grade pediatric primary brain tumor. It is found in the cerebellum, both centrally and peripherally. It is now classified with molecular modifiers that provide therapeutic possibilities. That tumor is covered by Drs Baker and Smith using a case example to guide a review of medulloblastoma subtypes. A case study is presented by Drs Drake and Ames to demonstrate three different methods that can be used to classify medulloblastoma into one of the four molecular subtypes.

The meningeal coverings of the brain are the most common brain tumor location, and the vast majority of these cases are meningiomas. These tumors of meningeal origin have three prognostic grades and multiple morphological varieties, now defined by the 2016 World Health Organization classification guidelines.1 Grading of meningiomas is presented by Dr Han. He will present three typical cases of meningiomas with a focus on grading. There are many histological variations of meningioma-possibly explaining the historical consideration of the names mesothelioma, meningothelioma, and leptomeningioma.5

Lastly, we focus on common pitfalls that may confuse or prolong the diagnostic process. All surgical pathologists know about the trap of miscalling fat necrosis liposarcoma. Similar possible pitfalls in neuropathology are also waiting in ambush for pathologists. There are numerous tumors that can resemble the histological appearance of other tumors. Even nonglial mesenchymal tumors and nonneoplastic gliosis can occasionally mimic gliomas. For many decades, astrocytomas have often impersonated oligodendrogliomas, but now molecular enhancements prevent that trap.6 Five common traps and pitfalls are presented by Dr Smith. This is followed by a rare case of cerebral blastomycosis, presented by Drs Hardy and Ames, which demonstrates diagnostic considerations in frozen section of suspected gliomas.

REFERENCES

1. Louis DN, Ohgaki H, Wiestler OD, et al. WHO Classification of Tumours of the Central Nervous System. Lyon, France: International Agency For Research On Cancer; 2016.
2. Russell DS, Rubinstein LJ. Pathology of Tumours of the Nervous System. London: Arnold; 1959.
3. Penfield W. The classification of gliomas and neuroglia cell types. Arch Neurol Psychiatry 1931;26:745.
4. Azzarelli R, Simons BD, Philpott A. The developmental origin of brain tumours: a cellular and molecular framework. Development 2018;145:dev162693.
5. Cushing H. Meningiomas: Their Classification, Regional Behavior, Life History, and Surgical End Result. Springfield, IL: Charles C Thomas; 1938.
6. Sahm F, Reuss D, Koelsche C, et al. Farewell to oligoastrocytoma: in situ molecular genetics favor classification as either oligodendroglioma or astrocytoma. Acta Neuropathol 2014;128:551–559.
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