Editing Brain tumor (section)

===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>