Editing Subarachnoid hemorrhage (section)

==Signs and symptoms==
The classic symptom of subarachnoid hemorrhage is [[thunderclap headache]] (a headache described as "like being kicked in the head",<ref name=Ox2007>{{cite book | vauthors = Longmore M, Wilkinson I, Turmezei T, Cheung CK |title=Oxford Handbook of Clinical Medicine, 7th edition |publisher=Oxford University Press |year=2007 |page=841 |isbn=978-0-19-856837-7}}</ref> or the "worst ever", developing over seconds to minutes). This headache often pulsates towards the [[occiput]] (the back of the head).<ref name="oxford2">{{cite book | vauthors = Ramrakha P, Moore K |title=Oxford Handbook of Acute Medicine, 2nd edition |publisher=Oxford University Press |year=2007 |pages=466–470 |isbn=978-0-19-852072-6}}</ref> About one-third of people have no symptoms apart from the characteristic headache, and about one in ten people who seek medical care with this symptom are later diagnosed with a subarachnoid hemorrhage.<ref name=VanGijn2007/> Vomiting may be present, and 1 in 14 have [[seizure]]s.<ref name=VanGijn2007/> [[Confusion]], decreased level of consciousness or [[coma]] may be present, as may neck stiffness and other signs of [[meningism]].<ref name=VanGijn2007/>

Neck stiffness usually presents six hours after initial onset of SAH.<ref name=OTV3>{{cite book |title=Oxford Textbook of Medicine | edition = Fourth | volume = 3 | vauthors = Warrell DA, Cox TM |year=2003 |publisher=Oxford |isbn=978-0-19-857013-4 |pages=1032–34|display-authors=etal}}</ref> Isolated [[pupillary response|dilation]] of a pupil and loss of the [[pupillary light reflex]] may reflect [[brain herniation]] as a result of rising [[intracranial pressure]] (pressure inside the skull).<ref name=VanGijn2007/> [[Intraocular hemorrhage]] (bleeding into the eyeball) may occur in response to the raised pressure: subhyaloid hemorrhage (bleeding under the [[vitreous membrane|hyaloid membrane]], which envelops the [[vitreous body]] of the eye) and vitreous hemorrhage may be visible on [[fundoscopy]]. This is known as [[Terson syndrome]] (occurring in 3–13 percent of cases) and is more common in more severe SAH.<ref name=mccarron>{{cite journal | vauthors = McCarron MO, Alberts MJ, McCarron P | title = A systematic review of Terson's syndrome: frequency and prognosis after subarachnoid haemorrhage | journal = Journal of Neurology, Neurosurgery, and Psychiatry | volume = 75 | issue = 3 | pages = 491–3 | date = March 2004 | pmid = 14966173 | pmc = 1738971 | doi = 10.1136/jnnp.2003.016816 }}</ref>

[[Oculomotor nerve]] abnormalities (affected eye looking downward and outward and [[ptosis (eyelid)|inability to lift the eyelid on the same side]]) or [[:wikt:palsy|palsy]] (loss of movement) may indicate bleeding from the [[posterior communicating artery]].<ref name=VanGijn2007/><ref name=oxford2/> Seizures are more common if the hemorrhage is from an aneurysm; it is otherwise difficult to predict the site and origin of the hemorrhage from the symptoms.<ref name=VanGijn2007/> SAH in a person known to have seizures is often diagnostic of a [[cerebral arteriovenous malformation]].<ref name=oxford2/>

The combination of intracerebral hemorrhage and raised intracranial pressure (if present) leads to a "sympathetic surge", i.e. over-activation of the sympathetic system. This is thought to occur through two mechanisms, a direct effect on the [[medulla oblongata|medulla]] that leads to activation of the descending [[sympathetic nervous system]] and a local release of inflammatory mediators that circulate to the peripheral circulation where they activate the sympathetic system. As a consequence of the sympathetic surge there is a sudden increase in [[blood pressure]]; mediated by increased [[Myocardial contractility|contractility]] of the [[ventricular system|ventricle]] and increased [[vasoconstriction]] leading to increased [[systemic vascular resistance]]. The consequences of this sympathetic surge can be sudden, severe, and are frequently life-threatening. The high [[blood plasma|plasma]] concentrations of adrenaline also may cause [[cardiac arrhythmia]]s (irregularities in the heart rate and rhythm), [[electrocardiogram|electrocardiographic changes]] (in 27 percent of cases)<ref name="OHA">{{cite book | vauthors = Allman KG, Wilson IH |title=Oxford Handbook of Anaesthesia | edition = 2nd |publisher=Oxford University Press |year=2006 |pages=408–409 |isbn=978-0-19-856609-0}}</ref> and [[cardiac arrest]] (in 3 percent of cases) may occur rapidly after the onset of hemorrhage.<ref name=VanGijn2007/><ref>{{cite journal | vauthors = Banki NM, Kopelnik A, Dae MW, et al | title = Acute neurocardiogenic injury after subarachnoid hemorrhage | journal = Circulation | volume = 112 | issue = 21 | pages = 3314–9 | date = November 2005 | pmid = 16286583 | doi = 10.1161/CIRCULATIONAHA.105.558239 | doi-access = free }}</ref> A further consequence of this process is [[neurogenic]] [[pulmonary edema]],<ref>{{cite journal| vauthors = O'Leary R, McKinlay J |title=Neurogenic pulmonary oedema|journal=[[Continuing Education in Anaesthesia, Critical Care & Pain]]|volume=11|issue=3|pages=87–92|doi=10.1093/bjaceaccp/mkr006|year=2011|s2cid=18066655|doi-access=free}}</ref> where a process of increased pressure within the pulmonary circulation causes leaking of fluid from the pulmonary [[capillaries]] into the air spaces, the [[Pulmonary alveolus|alveoli]], of the lung.<ref>{{cite journal |vauthors=Lee VH, Oh JK, Mulvagh SL, Wijdicks EF |title=Mechanisms in neurogenic stress cardiomyopathy after aneurysmal subarachnoid hemorrhage |journal=Neurocrit Care |volume=5 |issue=3 |pages=243–249 |date=2006 |pmid=17290097 |doi=10.1385/NCC:5:3:243 |s2cid=20268064 }}</ref><ref>{{cite journal |vauthors=Wartenberg KE, Mayer SA |title=Medical complications after subarachnoid hemorrhage: new strategies for prevention and management |journal=Curr Opin Crit Care |volume=12 |issue=2 |pages=78–84 |date=April 2006 |pmid=16543780 |doi=10.1097/01.ccx.0000216571.80944.65 |s2cid=29858980 }}</ref>

Subarachnoid hemorrhage may also occur in people who have had a head injury. Symptoms may include headache, decreased level of consciousness and [[hemiparesis]] (weakness of one side of the body). SAH is a frequent occurrence in traumatic brain injury and carries a poor prognosis if it is associated with deterioration in the level of consciousness.<ref>{{cite journal | vauthors = Servadei F, Murray GD, Teasdale GM, et al | title = Traumatic subarachnoid hemorrhage: demographic and clinical study of 750 patients from the European brain injury consortium survey of head injuries | journal = Neurosurgery | volume = 50 | issue = 2 | pages = 261–7; discussion 267–9 | date = February 2002 | pmid = 11844260 | doi = 10.1097/00006123-200202000-00006 | s2cid = 38900336 }}</ref>

While thunderclap headache is the characteristic symptom of subarachnoid hemorrhage, less than 10% of those with concerning symptoms have SAH on investigations.<ref name=Car2016/> A number of other causes may need to be considered.<ref name=Schwedt>{{cite journal | vauthors = Schwedt TJ, Matharu MS, Dodick DW | title = Thunderclap headache | journal = The Lancet. Neurology | volume = 5 | issue = 7 | pages = 621–31 | date = July 2006 | pmid = 16781992 | doi = 10.1016/S1474-4422(06)70497-5 | s2cid = 5511658 }}</ref>