NASAH in comparison with aneurysmal SAH. The risk of rebleeding depends on the underlying etiology of SAH. The risks of other complications likely vary according to the extent and location of bleeding. Patients with perimesencephalic SAH appear to have lower risk of complications than patients with NASAH due to other etiologies [7,90,91]. https://www.uptodate.com/contents/nonaneurysmal-subarachnoid-hemorrhage/print 12/32 7/7/23, 11:33 AM Nonaneurysmal subarachnoid hemorrhage - UpToDate In a retrospective single-center review of 138 patients with NASAH, vasospasm occurred in nearly 20 percent of those with diffuse SAH, similar to matched historical controls and higher than those with a perimesencephalic pattern of SAH [89]. Shunt-dependent hydrocephalus occurred in 14 percent of patients with NASAH in one retrospective series [92]. Associated risk factors included acute hydrocephalus, intraventricular hemorrhage, clinical vasospasm, and anticoagulation medication prior to SAH. Patients should receive other interventions to monitor, prevent, and treat complications of SAH. These are discussed separately. (See "Aneurysmal subarachnoid hemorrhage: Treatment and prognosis", section on 'Critical care management' and "Aneurysmal subarachnoid hemorrhage: Treatment and prognosis", section on 'Early complications' and "Aneurysmal subarachnoid hemorrhage: Treatment and prognosis", section on 'Vasospasm and delayed cerebral ischemia'.) The clinical features and management of complications of SAH are discussed in greater detail separately. (See "Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis", section on 'Complications'.) Interventions Interventions to prevent rebleeding and other etiologic-specific complications are individualized to the underlying etiology. (See 'Etiologies' above.) Prognosis In general, the prognosis for patients with NASAH is better than the prognosis for those with aneurysmal hemorrhage; however, NASAH represents a heterogenous group of patients and etiologies, and outcomes are largely dependent on the underlying cause and comorbidities [93,94]. (See 'Etiologies' above.) 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/nonaneurysmal-subarachnoid-hemorrhage/print 13/32 7/7/23, 11:33 AM Nonaneurysmal subarachnoid hemorrhage - 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 topic (see "Patient education: Subarachnoid hemorrhage (The Basics)") SUMMARY AND RECOMMENDATIONS Definition Approximately 20 percent of SAH cases are due to a cause other than a ruptured intracranial aneurysm. There are several potential causes of NASAH, and in some cases, the source of bleeding is not identified. (See 'Introduction' above.) Etiologies Underlying causes of spontaneous NASAH vary by clinical circumstances and location of bleeding. Common causes include (see 'Etiologies' above): Perimesencephalic NASAH Cerebral vascular malformations Intracranial arterial dissection Reversible cerebral vasoconstriction syndrome Cerebral venous thrombosis Cerebral amyloid angiopathy Minor or unsuspected trauma Spinal causes, such as vascular malformation, aneurysm, or tumor Clinical features The clinical presentation of NASAH varies by location and extent of the subarachnoid bleeding. Diffuse NASAH may mimic clinical features of aneurysmal SAH. Isolated SAH over the convexity may manifest with transient motor or sensory symptoms corresponding to underlying brain tissue. (See 'Clinical presentation' above.) Evaluation for underlying cause Imaging evaluation for underlying causes of bleeding is performed to identify or exclude etiologies that require specific treatment, to prevent complications, and to minimize morbidity. The selection of initial imaging testing varies by the distribution of SAH found on initial head CT ( image 2). (See 'Diagnostic evaluation' above.) Evaluation for patients with an aneurysmal SAH pattern Aneurysmal SAH pattern located in the basal cisterns, in the Sylvian or interhemispheric fissures, or diffusely https://www.uptodate.com/contents/nonaneurysmal-subarachnoid-hemorrhage/print 14/32 7/7/23, 11:33 AM Nonaneurysmal subarachnoid hemorrhage - UpToDate require initial angiographic evaluation to exclude a ruptured cerebral aneurysm as the cause of bleeding ( algorithm 1). (See 'Evaluation for patients with aneurysmal pattern of bleeding' above.) Initial angiographic imaging We prefer digital subtraction angiography (DSA) to assess for cerebral aneurysm because it is more sensitive than noninvasive imaging modalities. Angiography may also identify other vascular etiologies such as a vascular malformation or intracranial dissection. (See 'Initial imaging' above.) Subsequent testing Patients with an aneurysmal SAH pattern that is atypical for perimesencephalic SAH require additional imaging when initial angiography is unrevealing and the cause of bleeding is uncertain. Further diagnostic imaging typically includes MRI of the brain with contrast and repeat cerebral DSA. (See 'Subsequent testing when cerebral angiography is negative' above.) Some patients with a perimesencephalic SAH may warrant repeat cerebral DSA or noninvasive CT angiography if the initial study was felt to be technically inadequate or if rebleeding occurs. (See 'Patients with perimesencephalic SAH' above.) Evaluation for patients with isolated convexity SAH The evaluation of SAH that is isolated to the convexities of the cerebral hemispheres may be due to several causes and varies by clinical circumstances ( table 1). (See 'Evaluation for patients with isolated convexity SAH' above.) Management The approach to the general care and initial monitoring of patients with NASAH is the same as that for patients with aneurysmal SAH. (See 'Management and prognosis' above.) Supportive care All patients with SAH should be admitted to a facility with neurologic and/or neurosurgical expertise. Those with disabling neurologic symptoms or diffuse SAH should be admitted to an intensive care setting with the expertise to manage hemodynamic status and monitor for neurologic deterioration. (See 'Supportive care' above.) Complications Patients with NASAH may develop complications associated with aneurysmal SAH including hydrocephalus, vasospasm and cerebral ischemia, seizures, hyponatremia, and cardiac abnormalities. (See "Aneurysmal subarachnoid hemorrhage: Treatment and prognosis".) Interventions Interventions to prevent rebleeding and other etiologic-specific complications are individualized to the underlying etiology. (See 'Interventions' above.) https://www.uptodate.com/contents/nonaneurysmal-subarachnoid-hemorrhage/print 15/32 7/7/23, 11:33 AM Nonaneurysmal subarachnoid hemorrhage - UpToDate ACKNOWLEDGMENT The UpToDate editorial staff acknowledges David Brock, MD, CIP, who contributed to earlier versions of this topic review. Use of UpToDate is subject to the Terms of Use. REFERENCES 1. Rinkel GJ, Wijdicks EF, Hasan D, et al. Outcome in patients with subarachnoid haemorrhage and negative angiography according to pattern of haemorrhage on computed tomography. 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J Neurosci Nurs 2015; 47:E2. 94. Tsermoulas G, Flett L, Gregson B, Mitchell P. Immediate coma and poor outcome in subarachnoid haemorrhage are independently associated with an aneurysmal origin. Clin Neurol Neurosurg 2013; 115:1362. Topic 1111 Version 23.0 https://www.uptodate.com/contents/nonaneurysmal-subarachnoid-hemorrhage/print 22/32 7/7/23, 11:33 AM Nonaneurysmal subarachnoid hemorrhage - UpToDate GRAPHICS Perimesencephalic nonaneurysmal subarachnoid hemorrhage Head CT of three different patients demonstrating subarachnoid hemorrhage in the characteristic pattern of perimesencephalic hemorrhage with blood in the interpeduncular and ambient cisterns. CT: computed tomography. Images are courtesy of the Neuroradiology teaching le and the Neurosurgery Department at Thomas Je erson University Hospital. Graphic 76973 Version 5.0 https://www.uptodate.com/contents/nonaneurysmal-subarachnoid-hemorrhage/print 23/32 7/7/23, 11:33 AM Nonaneurysmal subarachnoid hemorrhage - 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 patients. In younger patients, it is usually due to RCVS, but in older ones, it often indicates amyloid angiopath a patient presenting with a severe rapid-onset headache, RCVS would be the likely diagnosis. (E) Traumatic SAH: the history usually suggests a traumatic SAH (the most common cause). However, if this pattern (dashed arrows indicate small amounts of SAH abutting bone, often in the anterior frontal and temp bones) is observed in a patient without a clear history of trauma, the likely cause is a traumatic SAH. https://www.uptodate.com/contents/nonaneurysmal-subarachnoid-hemorrhage/print 24/32 7/7/23, 11:33 AM Nonaneurysmal subarachnoid hemorrhage - UpToDate SAH: subarachnoid hemorrhage; CTA: computed tomography angiography; RCVS: reversible cerebral vasoconstriction syndrome. Reproduced from: Edlow JA. Managing Patients With Nontraumatic, Severe, Rapid-Onset Headache. Ann Emerg Med 2018; 71:400. Illus used with the permission of Elsevier Inc. All rights reserved. Graphic 121315 Version 1.0 https://www.uptodate.com/contents/nonaneurysmal-subarachnoid-hemorrhage/print 25/32 7/7/23, 11:33 AM Nonaneurysmal subarachnoid hemorrhage - UpToDate Diagnostic imaging evaluation to exclude secondary causes of subarachnoid hemorrhage Imaging evaluation is typically performed for patients with spontaneous SAH to identify or exclude a ruptured cerebral aneurysm. Evaluation for nonaneurysmal causes is also warranted for patients with isolated convexity SAH who present with bleeding restricted to the surface of the cerebral hemispheres and for other patients once ruptured aneurysm has been excluded. Further https://www.uptodate.com/contents/nonaneurysmal-subarachnoid-hemorrhage/print 26/32 7/7/23, 11:33 AM Nonaneurysmal subarachnoid hemorrhage - UpToDate imaging and/or other testing may be indicated for patients with acute SAH to monitor for complications and those who deteriorate clinically. Refer to UpToDate topic for additional details. SAH: subarachnoid hemorrhage; CT: computed tomography; DSA: digital subtraction angiography; CTA: computed tomographic angiography; MRI: magnetic resonance imaging. Refer to UpToDate topics for additional information on management of causes of SAH. Perimesencephalic pattern of acute SAH on head CT performed within 72 hours of onset consists of blood centered anterior to and in contact with the prepontine, interpeduncular, and/or suprasellar cisterns. Extent of blood on head CT should be restricted to the suprasellar, interpeduncular, crural, ambient, quadrigeminal, prepontine, and/or cerebellomedullary cisterns. Additional diagnostic testing is generally performed for patients with atypical features suggestive of a spinal source to bleeding such as those with prominent radicular symptoms and cervicomedullary location of bleeding or if the sensitivity of initial testing is limited by the presence of acute blood or vasospasm. Refer to UpToDate topic for additional details. Graphic 140106 Version 1.0 https://www.uptodate.com/contents/nonaneurysmal-subarachnoid-hemorrhage/print 27/32 7/7/23, 11:33 AM Nonaneurysmal subarachnoid hemorrhage - UpToDate Radiologic examples of perimesencephalic nonaneurysmal subarachnoid hemorrhage (A-D) CT and CTA of a 47-year-old woman nine hours after ictus demonstrating a PM-NASAH. (E-H) CT and CTA of a 62-year-old man seven hours after ictus demonstrating a PM-NASAH with blood in front of the medulla oblongata (arrow). https://www.uptodate.com/contents/nonaneurysmal-subarachnoid-hemorrhage/print 28/32 7/7/23, 11:33 AM Nonaneurysmal subarachnoid hemorrhage - UpToDate (I-L) CT and CTA of a 49-year-old woman 14 hours after ictus to illustrate a PM-NASAH with sedimentation of blood in the lateral horns (dashed arrows). (M-P) CT of a 66-year-old man 16 hours after ictus showing a PM-NASAH with the perimesencephalic cisterns filled with blood and associated hydrocephalus (M and N). CT on day seven after ictus showing a spontaneous decrease of hydrocephalus (O). CTA at time of presentation did not show an aneurysm (P). (Q-T) sagittal CT of a 47-year-old man four hours after ictus showing a PM-NASAH with distribution of blood in front of the brain stem and in the ambient cisterns. CT: computed tomography; CTA: computed tomography angiography; PM-NASAH: perimesencephalic subarachnoid hemorrhage From: Mensing LA, Vergouwen MDI, Laban KG, et al. Perimesencephalic Hemorrhage: A Review of Epidemiology, Risk Factors, Presumed Cause, Clinical Course, and Outcome. Stroke 2018; 49:1363. DOI: 10.1161/STROKEAHA.117.019843. Copyright 2018 American Heart Association. Reproduced with permission from Wolters Kluwer Health. Unauthorized reproduction of this material is prohibited. Graphic 118108 Version 3.0 https://www.uptodate.com/contents/nonaneurysmal-subarachnoid-hemorrhage/print 29/32 7/7/23, 11:33 AM Nonaneurysmal subarachnoid hemorrhage - UpToDate Characteristic features and initial diagnostic imaging for common underlying causes of spontaneous isolated convexity subarachnoid hemorrhage Suspected Choice of initial diagnostic Characteristic feature(s) etiology imaging test(s) Age >60 years CAA MRI brain with T2*-weighted SWI or GRE sequences Baseline cognitive impairment Recurrent thunderclap headache (>2 RCVS CTA or MRA of head within 1 week) MRI brain Exposure to vasoactive substance Risk factor for venous thrombosis* CVT CTV or MRV of head Head CT features suggestive of venous thrombosis (eg, hyperdense venous sinus; venous infarction) MRI brain New heart murmur Mycotic aneurysm MRI brain with contrast or cerebral DSA Systemic/cutaneous evidence of embolism Clinical history of active cancer Brain tumor MRI brain with contrast Clinical history of new persistent headaches Head CT features suggestive of tumor (eg, vasogenic edema) Headache prior to neurologic deficits Intracranial dissection CTA of head or cerebral DSA Clinical history of connective tissue disorder Head CT features suggestive of AVM AVM Cerebral DSA (calcification or hypodense flow voids adjacent to SAH) History of minor/occult trauma may be Occult trauma MRI brain elicited Evidence of extracranial bleeding or systemic injuries Clinical history of new persistent headaches Vasculitis MRI brain with contrast Cerebral DSA Progressive cognitive or other neurologic impairments Brain and meningeal biopsy https://www.uptodate.com/contents/nonaneurysmal-subarachnoid-hemorrhage/print 30/32 7/7/23, 11:33 AM Nonaneurysmal subarachnoid hemorrhage - UpToDate Patients with spontaneous isolated convexity SAH present with bleeding restricted to the surface of the cerebral hemispheres. The suspected underlying cause of convexity SAH may be identified by initial diagnostic imaging test. Additional imaging and/or other testing may be warranted if initial imaging is nondiagnostic. Refer to specific UpToDate topics for additional information on the diagnostic evaluation of conditions that may present with convexity SAH. SAH: subarachnoid hemorrhage; CAA: cerebral amyloid angiopathy; MRI: magnetic resonance imaging; SWI: susceptibility-weighted imaging; GRE: gradient recall echo imaging; RCVS: reversible cerebral vasoconstriction syndrome; CTA: computed tomographic angiography; MRA: magnetic resonance angiography; CT: computed tomography; CVT: cerebral venous thrombosis; CTV: computed tomography venography; MRV: magnetic resonance venography; DSA: digital subtraction angiography; AVM: arteriovenous malformation. Refer to UpToDate topic on the causes of venous thrombosis. Graphic 140108 Version 2.0 https://www.uptodate.com/contents/nonaneurysmal-subarachnoid-hemorrhage/print 31/32 7/7/23, 11:33 AM Nonaneurysmal subarachnoid hemorrhage - UpToDate Contributor Disclosures Farhan Siddiq, MD No relevant financial relationship(s) with ineligible companies to disclose. Jos Biller, MD, FACP, FAAN, FAHA No relevant financial relationship(s) with ineligible companies to disclose. Alejandro A Rabinstein, MD Grant/Research/Clinical Trial Support: Chiesi [Small investigator- initiated project]. Consultant/Advisory Boards: AstraZeneca [Secondary stroke prevention]; Brainomix [AI for stroke diagnostics]; Novo Nordisk [Stroke risk]; Shionogi [Stroke neuroprotection]. Other Financial Interest: Boston Scientific [Adverse event adjudication committee member for stroke risk reduction device in patients with atrial fibrillation]. All of the relevant financial relationships listed have been mitigated. Richard P Goddeau, Jr, DO, FAHA No relevant financial relationship(s) with ineligible companies to disclose. Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these are addressed by vetting through a multi-level review process, and through requirements for references to be provided to support the content. Appropriately referenced content is required of all authors and must conform to UpToDate standards of evidence. Conflict of interest policy https://www.uptodate.com/contents/nonaneurysmal-subarachnoid-hemorrhage/print 32/32