Editing Brain tumor (section)

==Pathophysiology==
===Meninges===
[[File:Meninges diagram.jpg|thumb|upright=1.3|The meninges lie between the skull and brain matter. Tumors originating from the meninges are meningiomas.]]
Human brains are surrounded by a system of [[connective tissue]] membranes called [[meninges]] that separate the [[Human brain|brain]] from the [[Human skull|skull]]. This three-layered covering is composed of (from the outside in) the [[dura mater]], [[arachnoid mater]], and [[pia mater]]. The arachnoid and pia are physically connected and thus often considered as a single layer, the ''leptomeninges''. Between the arachnoid mater and the pia mater is the [[subarachnoid space]] which contains [[cerebrospinal fluid]] (CSF). This fluid circulates in the narrow spaces between cells and through the cavities in the brain called [[Ventricular system|ventricles]], to support and protect the brain tissue. [[Blood vessels]] enter the [[central nervous system]] through the perivascular space above the pia mater. The cells in the blood vessel walls are joined tightly, forming the [[blood–brain barrier]] which protects the brain from [[toxins]] that might enter through the blood.<ref name=":7">{{Cite book|title=Clinically oriented anatomy| vauthors = Moore KL, Agur AM, Dalley II AF |isbn=978-1-4963-4721-3|edition= Eighth |location=Philadelphia|publisher=Lippincott Williams and Wilkins|oclc=978362025|date = September 2017}}</ref>

Tumors of the meninges are [[meningioma]]s and are often benign. Though not technically a tumor of brain tissue, they are often considered brain tumors since they protrude into the space where the brain is, causing symptoms. Since they are usually slow-growing tumors, meningiomas can be quite large by the time symptoms appear.<ref>{{Cite web|url=http://neurosurgery.ucla.edu/meningioma-brain-tumor|title=Meningioma Brain Tumor|website=neurosurgery.ucla.edu|access-date=29 July 2019}}</ref>

===Brain matter===
The three largest divisions of the brain are the [[Cerebrum|cerebral cortex]], [[cerebellum]] and the [[brainstem]].<ref name=":7" /> These areas are composed of two broad classes of cells: [[neurons]] and [[glia]]. These two cell types are equally numerous in the brain as a whole, although [[glial cells]] outnumber [[neurons]] roughly 4 to 1 in the [[cerebral cortex]]. Glia come in several types, which perform a number of critical functions, including structural support, metabolic support, insulation, and guidance of development.<ref>{{Cite web|url=https://training.seer.cancer.gov/brain/tumors/anatomy/neurons.html|title=Neurons & Glial Cells SEER Training|website=training.seer.cancer.gov|access-date=29 July 2019}}</ref> Primary tumors of the glial cells are called [[glioma]]s and often are malignant by the time they are diagnosed.<ref>{{cite journal | vauthors = Ostrom QT, Gittleman H, Farah P, Ondracek A, Chen Y, Wolinsky Y, Stroup NE, Kruchko C, Barnholtz-Sloan JS | title = CBTRUS statistical report: Primary brain and central nervous system tumors diagnosed in the United States in 2006-2010 | journal = Neuro-Oncology | volume = 15 | issue = Suppl 2 | pages = ii1-56 | date = November 2013 | pmid = 24137015 | pmc = 3798196 | doi = 10.1093/neuonc/not151 }}</ref>

The [[thalamus]] and [[hypothalamus]] are major divisions of the [[diencephalon]], with the [[pituitary gland]] and [[pineal gland]] attached at the bottom; tumors of the [[pituitary]]<ref>{{Cite web |title=Pituitary tumours |url=https://www.cancerresearchuk.org/about-cancer/brain-tumours/types/pituitary-tumours |archive-url=https://web.archive.org/web/20240301203755/https://www.cancerresearchuk.org/about-cancer/brain-tumours/types/pituitary-tumours |archive-date=1 March 2024 |access-date=18 April 2024 |website=www.cancerresearchuk.org |language=en}}</ref> and [[pineal gland]]<ref>{{Cite web |last=Kashani |first=Shayan |title=What to Know About Pineal Tumors |url=https://www.webmd.com/brain/what-to-know-about-pineal-tumors |access-date=2024-07-04 |website=WebMD |language=en}}</ref> are often benign.

The [[brainstem]] lies between the large cerebral cortex and the spinal cord. It is divided into the midbrain, pons, and medulla oblongata.<ref name=":7" />