is 83 to 98 percent [79-85]. Small aneurysms (especially 2 mm) may not be reliably identified. Although small aneurysms rupture less frequently than large aneurysms [86], they are more common, and rupture of small aneurysms (approximately 5 mm or less) accounts for nearly one- half of SAH cases [87-89]. Therefore, DSA should be performed if CTA does not reveal an aneurysm in a patient with SAH [41]. As technology improves, the sensitivity and specificity of noninvasive imaging is also likely to improve [90]. A 2011 meta-analysis of CTA diagnosis of intracranial aneurysms found that, compared with single-detector CTA, use of multidetector CTA was associated with an overall improved sensitivity and specificity for aneurysm detection (both >97 percent) as well as improved detection of smaller aneurysms 4 mm in diameter [91]. Another systematic review and meta-analysis restricted to patients with SAH had similar findings [92]. While a "spot sign" (ie, contrast extravasation) on CTA is associated with risk of hemorrhage expansion or rebleeding in patients with intracerebral hemorrhage, this is not the case for SAH [93,94]. It is likely that this sign, while appearing similar, actually reflects different processes when observed in SAH versus intracerebral hemorrhage. Patients with negative angiography Repeat angiography No angiographic cause of SAH is evident in 14 to 22 percent of cases. It is critical to repeat the angiogram in 4 to 14 days if the initial angiogram is negative. The recommended follow-up test in this setting is usually DSA. Up to 24 percent of all SAH patients with initial negative angiography have an aneurysm found on repeat angiography [95-99]. This may increase to as much as 49 percent if patients with perimesencephalic SAH and patients with normal CT scans are excluded [96]. Reasons for an initial false-negative angiogram include technical or reading errors, small aneurysm size, and obscuration of the aneurysm because of vasospasm, hematoma, or thrombosis within the aneurysm [95,96,100,101]. A third angiogram (DSA) at a period of two to three months is advocated by some, but is probably not necessary if the initial two studies are felt to be well-performed and expertly reviewed (see "Nonaneurysmal subarachnoid hemorrhage"). However, patients with SAH and a second negative angiogram should have a brain and spine MRI to look for possible vascular malformation of the brain or spinal cord [15]. https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 12/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate Nonaneurysmal SAH An estimated 15 to 20 percent of SAH cases are nonaneurysmal. The causes of nonaneurysmal SAH are potentially diverse, and include perimesencephalic hemorrhage, vascular malformations, intracranial arterial dissection, and a variety of other etiologies. The mechanism of bleeding in these cases is often not identified. (See "Nonaneurysmal subarachnoid hemorrhage".) Some patients with an initially negative angiogram have blood in the cisterns around the midbrain on head CT, which reflects a perimesencephalic pattern of hemorrhage ( image 2). Perimesencephalic hemorrhage accounts for about 10 percent of all cases of SAH and a majority of patients with nonaneurysmal SAH. Most patients with perimesencephalic hemorrhage do not have an aneurysm or other defined etiology. The need for repeat angiography in patients with perimesencephalic hemorrhage is discussed in detail separately. (See "Perimesencephalic nonaneurysmal subarachnoid hemorrhage", section on 'The role of repeat angiography' and "Nonaneurysmal subarachnoid hemorrhage", section on 'The role of repeat cerebral angiography'.) COMPLICATIONS A variety of early complications can occur with SAH, including rebleeding, hydrocephalus, cerebral edema, vasospasm and delayed cerebral ischemia, seizures, hyponatremia, cardiopulmonary abnormalities, and neuroendocrine dysfunction. These are discussed in detail separately. (See "Aneurysmal subarachnoid hemorrhage: Treatment and prognosis", section on 'Early complications'.) SOCIETY GUIDELINE LINKS Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Stroke in adults".) INFORMATION FOR PATIENTS UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." th th The Basics patient education pieces are written in plain language, at the 5 to 6 grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more th th sophisticated, and more detailed. These articles are written at the 10 to 12 grade reading https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 13/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate level and are best for patients who want in-depth information and are comfortable with some medical jargon. Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.) Basics topics (see "Patient education: Hemorrhagic stroke (The Basics)" and "Patient education: Brain aneurysm (The Basics)" and "Patient education: Subarachnoid hemorrhage (The Basics)") Beyond the Basics topics (see "Patient education: Stroke symptoms and diagnosis (Beyond the Basics)" and "Patient education: Hemorrhagic stroke treatment (Beyond the Basics)") SUMMARY AND RECOMMENDATIONS Clinical presentation The overwhelming majority of patients with aneurysmal subarachnoid hemorrhage (SAH) present with a sudden-onset severe headache, which may be associated with brief loss of consciousness, seizures, nausea or vomiting, or meningismus. (See 'Clinical presentation' above.) Evaluation and diagnosis Sudden onset of headache, regardless of severity or prior headache history, should raise the clinical suspicion for SAH and compel a diagnostic evaluation. (See 'Evaluation and diagnosis' above.) Imaging Noncontrast head computed tomography (CT) reveals the diagnosis in more than 90 percent of cases if performed within 24 hours of bleeding onset. (See 'Head CT scan' above.) Lumbar puncture Lumbar puncture is mandatory if there is a strong suspicion of SAH despite a normal head CT, with the disputed exception of select patients with isolated headache and normal examination presenting early and scanned within six hours of headache onset. (See 'Lumbar puncture' above.) The classic findings are an elevated opening pressure, an elevated red blood cell count that does not diminish from cerebrospinal fluid (CSF) tube 1 to tube 4, and xanthochromia. Immediate centrifugation of the CSF can help differentiate bleeding in SAH from that due to a traumatic spinal tap. https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 14/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate Identifying the source of bleeding Once a diagnosis of SAH has been made, the etiology of the hemorrhage must be determined with vascular imaging. Of the available tests, digital subtraction angiography (DSA) has the highest resolution to detect intracranial aneurysms and define their anatomic features and remains the gold standard test for this, but CT angiography is being increasingly used as a first-line vascular test. (See 'Identifying the source of bleeding' above.) Repeat angiography is necessary if the initial study is negative, unless the pattern of hemorrhage is perimesencephalic, in which a repeat angiography may be considered optional. Additional testing is required for SAH that is nonaneurysmal. (See 'Patients with negative angiography' above.) Use of UpToDate is subject to the Terms of Use. REFERENCES 1. Edlow JA, Caplan LR. Avoiding pitfalls in the diagnosis of subarachnoid hemorrhage. N Engl J Med 2000; 342:29. 2. Perry JJ, Stiell IG, Sivilotti ML, et al. Clinical decision rules to rule out subarachnoid hemorrhage for acute headache. JAMA 2013; 310:1248. 3. Perry JJ, Sivilotti MLA, Sutherland J, et al. Validation of the Ottawa Subarachnoid Hemorrhage Rule in patients with acute headache. CMAJ 2017; 189:E1379. 4. Perry JJ, Stiell IG, Sivilotti ML, et al. High risk clinical characteristics for subarachnoid haemorrhage in patients with acute headache: prospective cohort study. BMJ 2010; 341:c5204. 5. Perry DC, Bruce C. Evaluating the child who presents with an acute limp. BMJ 2010; 341:c4250. 6. Claassen J, Park S. Spontaneous subarachnoid haemorrhage. Lancet 2022; 400:846. 7. Schievink WI. Intracranial aneurysms. 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Topic 1130 Version 27.0 https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 22/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate GRAPHICS Hunt and Hess grading system for patients with subarachnoid hemorrhage Grade Neurologic status 1 Asymptomatic or mild headache and slight nuchal rigidity 2 Severe headache, stiff neck, no neurologic deficit except cranial nerve palsy 3 Drowsy or confused, mild focal neurologic deficit 4 Stuporous, moderate or severe hemiparesis 5 Coma, decerebrate posturing Based upon initial neurologic examination. Adapted from: Hunt W, Hess R. Surgical risk as related to time of intervention in the repair of intracranial aneurysms. J Neurosurg 1968; 28:14. Graphic 69179 Version 5.0 https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 23/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate Focal physical findings in patients with subarachnoid hemorrhage Findings Likely cause Third nerve palsy Usually posterior communicating aneurysm; also posterior cerebral artery and superior cerebellar artery aneurysms Sixth nerve palsy Elevated intracranial pressure (false localizing sign) Combination of hemiparesis and aphasia or visuospatial neglect Middle cerebral artery aneurysm, thick subarachnoid clots, or parenchymal hematomas Bilateral leg weakness and abulia Anterior communicating artery aneurysm Ophthalmoplegia Internal carotid artery aneurysm impinging upon the cavernous sinus Unilateral visual loss or bitemporal hemianopia Internal carotid artery aneurysm compressing optic nerve or optic chiasm Impaired level of consciousness and impaired Pressure on the dorsal midbrain due to upward gaze hydrocephalus Brainstem signs Brainstem compression by basilar artery aneurysm Neck stiffness Meningeal irritation by the presence of subarachnoid blood Retinal and subhyaloid hemorrhages Sudden increase of intracranial pressure Preretinal hemorrhages (Terson syndrome) Vitreous hemorrhage due to severe elevations of intracranial pressure From: Suarez JI. Diagnosis and Management of Subarachnoid Hemorrhage. Continuum (Minneap Minn) 2015; 21:1263. DOI: 10.1212/CON.0000000000000217. Copyright 2015 American Academy of Neurology. Reproduced with permission from Wolters Kluwer Health. Unauthorized reproduction of this material is prohibited. Graphic 121321 Version 2.0 https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 24/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate World Federation of Neurological Surgeons subarachnoid hemorrhage grading scale Grade GCS score Motor deficit 1 15 Absent 2 13 to 14 Absent 3 13 to 14 Present 4 7 to 12 Present or absent 5 3 to 6 Present or absent GCS: Glasgow Coma Scale. Data from: Report of World Federation of Neurological Surgeons Committee on a Universal Subarachnoid Hemorrhage Grading Scale. J Neurosurg 1988; 68:985. Graphic 65468 Version 3.0 https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 25/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate Glasgow Coma Scale (GCS) Score Eye opening Spontaneous 4 Response to verbal command 3 Response to pain 2 No eye opening 1 Best verbal response Oriented 5 Confused 4 Inappropriate words 3 Incomprehensible sounds 2 No verbal response 1 Best motor response Obeys commands 6 Localizing response to pain 5 Withdrawal response to pain 4 Flexion to pain 3 Extension to pain 2 No motor response 1 Total The GCS is scored between 3 and 15, 3 being the worst and 15 the best. It is composed of three parameters: best eye response (E), best verbal response (V), and best motor response (M). The components of the GCS should be recorded individually; for example, E2V3M4 results in a GCS score of 9. A score of 13 or higher correlates with mild brain injury, a score of 9 to 12 correlates with moderate injury, and a score of 8 or less represents severe brain injury. Graphic 81854 Version 9.0 https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 26/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate [1] Fisher grade of cerebral vasospasm risk in subarachnoid hemorrhage Group Appearance of blood on head CT scan 1 No blood detected 2 Diffuse deposition or thin layer with all vertical layers (in interhemispheric fissure, insular cistern, ambient cistern) less than 1 mm thick 3 Localized clot and/or vertical layers 1 mm or more in thickness 4 Intracerebral or intraventricular clot with diffuse or no subarachnoid blood CT: computed tomography. Reference: 1. Fisher CM, Kistler JP, Davis JM. Relation of cerebral vasospasm to subarachnoid hemorrhage visualized by CT scanning. Neurosurgery 1980; 6:1. Graphic 81122 Version 4.0 https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 27/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate Modified Fisher (Claassen) subarachnoid hemorrhage CT rating scale Grade Head CT criteria 0 No SAH or IVH 1 Minimal SAH and no IVH 2 Minimal SAH with bilateral IVH 3 Thick SAH (completely filling one or more cistern or fissure) without bilateral IVH 4 Thick SAH (completely filling one or more cistern or fissure) with bilateral IVH CT: computed tomography; SAH: subarachnoid hemorrhage; IVH: intraventricular hemorrhage. From: Claassen J, Bernardini GL, Kreiter K, et al. E ect of cisternal and ventricular blood on risk of delayed cerebral ischemia after subarachnoid hemorrhage: the Fisher scale revisited. Stroke 2001; 32:2012. Graphic 57558 Version 5.0 https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 28/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate Ogilvy and Carter grading system to predict outcome for surgical management of intracranial aneurysms Criteria Points Age 50 or less 0 Age greater than 50 1 Hunt and Hess grade 0 to 3 (no coma) 0 Hunt and Hess grade 4 and 5 (in coma) 1 Fisher scale score 0 to 2 0 Fisher scale score 3 and 4 1 Aneurysm size 10 mm or less 0 Aneurysm size greater than 10 mm 1 Giant posterior circulation aneurysm size 25 mm or more 1 The total score ranges from 0 to 5, corresponding to grades 0 to 5 Adapted from: Ogilvy CS, Carter BS. A proposed comprehensive grading system to predict outcome for surgical management of intracranial aneurysms. Neurosurgery 1998; 42:959. Graphic 70705 Version 4.0 https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 29/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate [1] Reasons for misdiagnosis of subarachnoid hemorrhage Failure to recognize spectrum of presentation of subarachnoid hemorrhage Not obtaining complete history from patients with unusual (for the patient) headaches Is the onset abrupt? Is the quality different and severity greater than prior headaches? Failure to appreciate that the headache can improve spontaneously or with non-narcotic analgesics Focusing on the secondary head injury resulting from syncope and fall or motor vehicle collision Focusing on ECG abnormalities Focusing on elevated blood pressure Overreliance on the classic presentation Misdiagnosis of other disorders (eg, viral syndrome, viral meningitis, migraine, tension-type headache, sinus-related headache, psychiatric disorder) Failure to understand the limitations of head CT scanning Sensitivity decreases as onset of headache increases False-negative results with small-volume bleeds Scan interpreted by inexperienced physician Motion artifacts or lack of thin cuts of posterior fossa False-negative results due to hematocrit of less than 30% Failure to perform lumbar puncture or interpret the CSF findings correctly Failure to perform lumbar puncture in patients with negative or inconclusive CT scans Failure to distinguish a traumatic tap from true subarachnoid hemorrhage Failure to recognize that xanthochromia may be absent very early (less than 12 hours) and very late (more than 2 weeks) ECG: electrocardiogram; CT: computed tomography; CSF: cerebrospinal fluid. Reference: 1. Suarez JI. Diagnosis and Management of Subarachnoid Hemorrhage. Continuum (Minneap Minn) 2015; 21:1263. Original gure modi ed for this publication. From: Edlow JA, Malek AM, Ogilvy CS. Aneurysmal subarachnoid hemorrhage: update for emergency physicians. J Emerg Med 2008; 34:237. Table used with the permission of Elsevier Inc. All rights https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 30/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate reserved. Graphic 121322 Version 1.0 https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 31/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate Etiologies of thunderclap headache Most common causes of thunderclap headache: Subarachnoid hemorrhage Reversible cerebral vasoconstriction syndromes (RCVS) Conditions that less commonly cause thunderclap headache: Cerebral infection (eg, meningitis, acute complicated sinusitis) Cerebral venous thrombosis Cervical artery dissection Spontaneous intracranial hypotension Acute hypertensive crisis Posterior reversible leukoencephalopathy syndrome (PRES) Intracerebral hemorrhage Ischemic stroke Conditions that uncommonly or rarely cause thunderclap headache: Pituitary apoplexy Colloid cyst of the third ventricle Aortic arch dissection Aqueductal stenosis Brain tumor Giant cell arteritis Pheochromocytoma Pneumocephalus Retroclival hematoma Spinal epidural hematoma Varicella zoster virus vasculopathy Vogt-Koyanagi-Harada syndrome Disputed causes of thunderclap headache: Sentinel headache (unruptured intracranial aneurysm)* Primary thunderclap headache Sentinel headache due to an unruptured intracranial aneurysm is a possible cause of thunderclap headache, but supporting data are weak. https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 32/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate There is controversy as to whether thunderclap headache can occur as a benign and potentially recurrent headache disorder in the absence of underlying organic intracranial pathology. Graphic 81710 Version 8.0 https://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-clinical-manifestations-and-diagnosis/print 33/38 7/7/23, 11:26 AM Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis - UpToDate Various radiologic patterns of subarachnoid hemorrhage on noncontrast compu tomography (CT) of the head (A) Obvious large SAH: hyperdense blood in all the basal cisterns, with some dilatation of the temporal horn the lateral ventricles, suggesting early hydrocephalus. (B) More subtle, smaller SAH: small hyperdense collection of blood in the basal cistern adjacent to the left p and suprasellar cistern (short solid arrow). (C) Perimesencephalic SAH: the long solid arrows indicate a perimesencephalic (sometimes called a pretrun SAH. These hemorrhages represent approximately 10% of nontraumatic SAHs. They are thought to be caused venous bleeding, will have a negative CTA result, and usually have an excellent outcome. However, the radiographic pattern is also observed with posterior circulation aneurysms, so all of these patients require neurosurgical consultation and vascular imaging. (D) Convexal SAH: the arrowheads indicate a high convexal SAH. This pattern is observed in two groups of