Hydrocephalus

==Mechanism==
[[File:Intracerebral hemorrhage.jpg|thumb|upright=1.2|Spontaneous [[intracerebral hemorrhage|intracerebral]] and [[intraventricular hemorrhage]] with hydrocephalus shown on CT scan<ref name="Yadav07">{{cite journal | vauthors = Yadav YR, Mukerji G, Shenoy R, Basoor A, Jain G, Nelson A | title = Endoscopic management of hypertensive intraventricular haemorrhage with obstructive hydrocephalus | journal = BMC Neurology | volume = 7 | pages = 1 | date = January 2007 | pmid = 17204141 | pmc = 1780056 | doi = 10.1186/1471-2377-7-1 | doi-access = free }}</ref>]]
[[File:3DPX-003132 Cast of Lateral ventricles in Hydrocephaly NevitDilmen.stl|thumb|3D cast of lateral ventricles in hydrocephalus]]
Hydrocephalus is usually due to blockage of CSF outflow in the ventricles or in the subarachnoid space over the brain. In a person without hydrocephalus, CSF continuously circulates through the brain, its ventricles and the [[spinal cord]] and is continuously drained away into the circulatory system. Alternatively, the condition may result from an overproduction of the CSF, from a congenital malformation blocking normal drainage of the fluid, or from complications of head injuries or infections.<ref>{{cite web |url=http://www.ninds.nih.gov/disorders/hydrocephalus/detail_hydrocephalus.htm |title=Hydrocephalus Fact Sheet |archive-url=https://web.archive.org/web/20160727231854/http://www.ninds.nih.gov/disorders/hydrocephalus/detail_hydrocephalus.htm |archive-date=2016-07-27 |work=National Institute of Neurological Disorders and Stroke |date=August 2005}}</ref>

Compression of the brain by the accumulating fluid eventually may cause neurological symptoms such as [[convulsions]], [[intellectual disability]], and [[epileptic seizure]]s. These signs occur sooner in adults, whose skulls are no longer able to expand to accommodate the increasing fluid volume within. Fetuses, infants, and young children with hydrocephalus typically have an abnormally large head, excluding the face, because the pressure of the fluid causes the individual skull bones—which have yet to fuse—to bulge outward at their [[juncture points]]. Another [[medical sign]], in infants, is a characteristic fixed downward gaze with whites of the eyes showing above the iris, as though the infant were trying to examine its own lower eyelids.<ref>{{cite book | vauthors = Cabot RC | date = 1919 | title = Physical diagnosis | publisher = William Wood and Company | location = New York | edition = 7th | page = 5 | via = Google Books }}</ref>

The elevated ICP may cause compression of the brain, leading to brain damage and other complications. A complication often overlooked is the possibility of hearing loss due to ICP. The mechanism of ICP on hearing loss is presumed that the transmission of CSF pressure to and from the Perilymphatic space through a patent cochlear aqueduct.<ref name=":2">{{cite journal | vauthors = Pogodzinski MS, Shallop JK, Sprung J, Weingarten TN, Wong GY, McDonald TJ | title = Hearing loss and cerebrospinal fluid pressure: case report and review of the literature | journal = Ear, Nose, & Throat Journal | volume = 87 | issue = 3 | pages = 144–147 | date = March 2008 | pmid = 18404909 | doi = 10.1177/014556130808700308 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Marchbanks RJ, Reid A | title = Cochlear and cerebrospinal fluid pressure: their inter-relationship and control mechanisms | journal = British Journal of Audiology | volume = 24 | issue = 3 | pages = 179–187 | date = June 1990 | pmid = 2194603 | doi = 10.3109/03005369009076554 }}</ref> The cochlear aqueduct connects the Perilymphatic space of the inner ear with the subarachnoid space of the posterior cranial fossa.<ref name=":3">{{cite journal | vauthors = Lim HW, Shim BS, Yang CJ, Kim JH, Cho YH, Cho YS, Kong DS, Koo JW, Han JH, Chung JW | display-authors = 6 | title = Hearing loss following ventriculoperitoneal shunt in communicating hydrocephalus patients: a pilot study | journal = The Laryngoscope | volume = 124 | issue = 8 | pages = 1923–1927 | date = August 2014 | pmid = 24318317 | doi = 10.1002/lary.24553 | s2cid = 24667376 }}</ref> A loss of CSF pressure can induce Perilymphatic loss or endolymphatic hydrops resembling the clinical presentation of [[Ménière's disease]] associated hearing loss in the low frequencies.<ref name=":2" />

CSF can accumulate within the ventricles, this condition is called internal hydrocephalus and may result in increased CSF pressure. The production of CSF continues, even when the passages that normally allow it to exit the brain are blocked. Consequently, fluid builds inside the brain, causing pressure that dilates the ventricles and compresses the [[nervous tissue]]. Compression of the nervous tissue usually results in [[irreversible brain damage]]. If the [[human skull|skull]] bones are not completely [[ossified]] when the hydrocephalus occurs, the pressure may also severely enlarge the head. The [[Aqueductal stenosis|cerebral aqueduct]] may be blocked at the time of [[birth]] or may become blocked later in life because of a tumor growing in the [[brainstem]].<ref>{{Cite web |date=2017-12-07 |title=Hydrocephalus: Causes, symptoms, and treatments |url=https://www.medicalnewstoday.com/articles/181727 |access-date=2022-05-18 |website=www.medicalnewstoday.com |language=en}}</ref>