Nonaneurysmal subarachnoid hemorrhage

INTRODUCTION — Subarachnoid hemorrhage (SAH) refers to intracranial bleeding within the subarachnoid space, which lies between the arachnoid and pia mater overlying the brain. Most cases of spontaneous (nontraumatic) SAH are caused by rupture of an intracranial aneurysm. However, approximately 20 percent of SAH cases are not due to a ruptured intracranial aneurysm. The potential causes of nonaneurysmal SAH (NASAH) are diverse; in some cases, the source of bleeding is not identified.

This topic will review the etiologies, diagnostic evaluation, and management of NASAH. Aneurysmal SAH is discussed separately.

●(See "Aneurysmal subarachnoid hemorrhage: Epidemiology, risk factors, and pathogenesis".)

●(See "Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis".)

●(See "Aneurysmal subarachnoid hemorrhage: Treatment and prognosis".)

Traumatic SAH and other forms of traumatic brain injury are presented separately. (See "Management of acute moderate and severe traumatic brain injury".)

ETIOLOGIES

Perimesencephalic nonaneurysmal subarachnoid hemorrhage — Perimesencephalic NASAH is a subtype of NASAH identified by a specific pattern of localized blood on computed tomography (CT) of the head and generally characterized by a benign course that distinguishes these patients not only from aneurysmal SAH, but also from other patients with NASAH [1-4].

The head CT findings that define perimesencephalic NASAH include blood isolated to the perimesencephalic cisterns anterior to the brainstem; there may be extension into the ambient cisterns or basal parts of the Sylvian fissures but not into the lateral Sylvian fissure, anterior interhemispheric fissure, or lateral ventricles (image 1 and image 2) [4,5].

Perimesencephalic NASAH may be caused by spontaneous rupture of a small perforating artery or vein at the surface of the brainstem. However, in most cases, diagnostic testing is unable to definitively identify the cause of bleeding in perimesencephalic NASAH. In some case series, perimesencephalic NASAH accounts for up to two-thirds of patients with NASAH [5].

Perimesencephalic NASAH is discussed in detail separately. (See "Perimesencephalic nonaneurysmal subarachnoid hemorrhage".)

Vascular malformations — Approximately 10 percent of SAH are caused by vascular malformations [6,7]. Vascular malformations of the brain include arteriovenous malformations, dural arteriovenous fistulas, cavernous malformations, developmental venous anomalies, and capillary telangiectasias.

Intracerebral hemorrhage is the most common hemorrhagic presentation, but vascular malformations near the surface of the brain may present with bleeding primarily or exclusively in the subarachnoid space [6,8-11]. Vascular malformations of the brain that most frequently present with SAH are arteriovenous malformations and dural arteriovenous fistulas. Dural arteriovenous fistulas with cortical venous drainage are associated with high risk for early rebleeding [10,12].

Most vascular malformations can be visualized on cerebral angiography [9,13,14]. Angiographically occult vascular malformations such as some cavernous malformations, developmental venous anomalies, and capillary telangiectasias are visualized on magnetic resonance imaging (MRI) but are less likely to be a source of intracranial bleeding, including SAH.

Vascular malformations of the brain are discussed in greater detail separately. (See "Brain arteriovenous malformations" and "Vascular malformations of the central nervous system".)

Intracranial arterial dissection — Dissection of an intracranial artery can produce SAH. Intracranial dissection is usually initiated by a tear in the media, producing an intramural hemorrhage [15]. When the tear extends through (or is initiated in) the intima, a false lumen forms and can lead to narrowing of the (true) lumen with subsequent thrombus formation and thromboembolic ischemic stroke. However, if the dissection tears through the adventitia, SAH may occur. SAH is more common with dissections in the vertebrobasilar circulation than the intracranial carotid circulations. If intracranial dissection causes SAH, bleeding is massive and often devastating [16-18].

Many intracranial dissections are believed to occur in the setting of sudden or unusual stretching of arteries, but such a clinical history is often lacking. While connective tissue diseases such as Ehlers-Danlos syndrome type IV and fibromuscular dysplasia are associated with intracranial arterial dissection, most patients with dissection do not have these conditions. Other risk factors for intracranial dissection include migraine and hypertension.

Most cases of intracranial arterial dissection in the setting of SAH are diagnosed by conventional cerebral angiography [1,15,17]. Brain MRI with T1-weighted fat saturation sequences may identify acute intramural hemorrhage as a crescent-shaped hyperdensity adjacent to the arterial lumen on cross-sectional images [15]. The clinical features and diagnosis of intracranial arterial dissections are discussed in greater detail separately. (See "Cerebral and cervical artery dissection: Clinical features and diagnosis".)

Intracranial dissections are typically treated surgically or with endovascular interventions due to the high risk of morbidity with rebleeding, but natural history data are limited. (See "Cerebral and cervical artery dissection: Treatment and prognosis", section on 'Subarachnoid hemorrhage due to intracranial dissection'.)

Reversible cerebral vasoconstriction syndrome — Reversible cerebral vasoconstriction syndrome (RCVS) is a condition characterized by multifocal narrowing of the cerebral arteries and a clinical presentation that typically features recurrent thunderclap headaches with or without neurologic deficits. Patients with severe vasospasm may present with ischemic stroke, cerebral edema, and hemorrhagic complications, including SAH, often within the hemispheric convexities. In case series, convexity SAH was present in 33 percent of patients with RCVS [19]. RCVS is thought to involve vasospasm that may be triggered by vasoactive and other medications, medical conditions, or environmental stimuli, but an associated trigger is frequently not identified.

The presence of recurrent thunderclap headaches is a clinical clue used to distinguish RCVS from aneurysmal SAH. Vascular imaging frequently shows widespread, multifocal narrowing of the cerebral arteries. Cerebral angiography is warranted for patients with atypical symptoms such as those presenting with a single instance of a thunderclap headache or those with SAH at the basal cisterns or Sylvian or interhemispheric fissures. Brain imaging in RCVS may show focal SAH typically within the convexities of one or both cerebral hemispheres. Ischemic lesions may be found at border-zone regions of adjacent vascular territories.

The management of RCVS is typically supportive, although calcium channel blockers and magnesium sulfate have been used for vasospasm and headaches. Vasoconstriction typically resolves within several weeks. RCVS is discussed in greater detail separately. (See "Reversible cerebral vasoconstriction syndrome".)

Cerebral venous thrombosis — Cerebral venous thrombosis (CVT) causes increased venous pressure that can lead to the development of cerebral edema, venous infarction, and/or hemorrhage. CVT can also present with SAH as its primary manifestation [6,20-24]. The clinical presentation of CVT commonly includes headache with or without focal neurologic symptoms. Onset is typically less abrupt than with aneurysmal rupture and bleeding on neuroimaging is frequently localized and superficial rather than at the basal cisterns.

CVT may be visualized on noninvasive vascular studies such as a CT or magnetic resonance (MR) venogram or on the venous phase of digital subtraction angiography (DSA) and/or on brain MRI. Management typically includes anticoagulation, even for most patients with hemorrhagic presentations.

CVT is discussed in detail separately. (See "Cerebral venous thrombosis: Etiology, clinical features, and diagnosis" and "Cerebral venous thrombosis: Treatment and prognosis".)

Cerebral amyloid angiopathy — Cerebral amyloid angiopathy (CAA) most commonly presents with lobar intracerebral brain hemorrhage (ICH), but isolated convexity SAH may also occur. Subarachnoid bleeding may be focal, often restricted to a single sulcus. Associated imaging findings include chronic cortical microbleeds, superficial siderosis, and bilateral subcortical white matter hyperintensities [25-28]. Clinical symptoms vary by location and extent of acute bleeding. Some patients with convexity SAH may present with transient focal neurologic episodes.

CAA is typically diagnosed by characteristic findings on brain MRI that includes T2*-susceptibility-weighted or gradient-echo sequences. Pathologic confirmation is generally reserved for patients with atypical features.

The clinical presentation, diagnostic findings, and management of CAA are discussed in detail separately. (See "Cerebral amyloid angiopathy".)

Traumatic SAH — Trauma is a common cause of intracranial bleeding, including SAH, but is usually identified by the clinical setting. However, the appropriate clinical history may be unavailable for patients who present with confusion or stupor or baseline cognitive impairment, or in the setting of minor trauma not reported or recalled by the patient. In these settings, radiologic clues of a traumatic origin include localized bleeding in superficial sulci, adjacent skull fracture, cerebral contusion, as well as external evidence of traumatic injury [8,29]. Awake patients and any witnesses should be questioned about possible trauma as the cause to SAH. For patients with moderate to severe traumatic brain injury, brain MRI may also show other features typically associated with additional forms of brain injury (eg, intracerebral hemorrhage, diffuse axonal injury) (image 2). (See "Acute mild traumatic brain injury (concussion) in adults" and "Management of acute moderate and severe traumatic brain injury".)

While trauma can be the cause of SAH, SAH may also lead to trauma (eg, fall). Diagnostic evaluation including cerebral DSA may be indicated for some patients with trauma and SAH when history or imaging pattern of SAH suggests that a ruptured intracranial aneurysm or other etiology may have caused the SAH. (See 'Diagnostic evaluation' below.)

Spinal lesions — Up to 10 percent of patients with spinal vascular malformations present with SAH [8,30,31]. Dural arteriovenous fistulas are the most common type of spinal vascular malformation [32]. Those that cause SAH are usually, but not always, located in the cervical cord or craniocervical junction [33]. Prominent back or neck pain or myelopathic signs at presentation can indicate this source, but these are often absent and the clinical appearance can mimic that of intracranial aneurysm rupture [33-36]. (See "Disorders affecting the spinal cord", section on 'Vascular malformations'.)

Ruptured spinal aneurysms are a rare source of bleeding in patients with SAH. These patients usually present with prominent neck or back pain and myelopathic or radicular symptoms that localize to one or more spinal roots [37,38].

Vascular malformations and aneurysms in the spine can be difficult to visualize with cerebral neuroimaging testing [8,33,34]. Cerebral DSA performed to exclude more common intracranial aneurysms may not identify spinal lesions. The diagnosis may be delayed until the patient presents with recurrent SAH. Acute brain imaging may show SAH that predominates in the caudal areas of the brainstem. However, dedicated spinal DSA is typically required to identify these lesions. Spinal vascular malformations and aneurysms are generally managed by neurosurgical and/or endovascular interventions. (See "Disorders affecting the spinal cord", section on 'Vascular malformations'.)

Uncommon etiologies

●Primary and metastatic brain tumors have been reported to produce SAH as the presenting manifestation [6,39,40]. (See "Overview of the clinical features and diagnosis of brain tumors in adults".)

●Moyamoya disease is associated with cerebral aneurysms that can rupture and produce SAH; however, NASAH may also occur from rupture of the fragile transdural anastomotic vessels [41,42]. (See "Moyamoya disease and moyamoya syndrome: Etiology, clinical features, and diagnosis".)

●Pituitary apoplexy often presents with sudden onset of headache and vomiting, and there can be prominent subarachnoid blood on head CT, which may obscure visualization of the pituitary adenoma [43-46]. Pituitary apoplexy is usually heralded by vision change and is accompanied by oculomotor nerve palsies. If not identified on the initial CT scan, brain MRI with dedicated pituitary sequences should be performed [47,48]. (See "Causes of hypopituitarism", section on 'Pituitary apoplexy'.)

●Spontaneous intracranial hypotension may present with orthostatic headache and NASAH, typically in the setting of acute worsening of symptoms [49,50]. Diagnosis of spontaneous intracranial hypotension is typically by brain MRI or myelography. (See "Spontaneous intracranial hypotension: Pathophysiology, clinical features, and diagnosis".)

●Cerebral vasculitis frequently presents with headache and progressive neurologic symptoms. Acute presentations including ischemic stroke with or without convexity SAH may also occur [51]. (See "Primary angiitis of the central nervous system in adults" and "Overview of and approach to the vasculitides in adults" and "Clinical manifestations and diagnosis of rheumatoid vasculitis", section on 'Neurologic disease'.)

●Cerebral hyperperfusion syndrome after carotid endarterectomy or angioplasty with or without stenting and reversible posterior leukoencephalopathy syndrome typically presents with neurologic symptoms due to focal cerebral edema and disruption of the blood-brain barrier, the latter of which may produce convexity SAH [25,28,52-55]. (See "Complications of carotid endarterectomy", section on 'Hyperperfusion syndrome' and "Reversible posterior leukoencephalopathy syndrome".)

●Several infectious agents that may cause meningitis or meningoencephalitis may also present with SAH. These include several bacterial sources (eg, Streptococcus pneumoniae, Staphylococcus aureus, Neisseria meningitidis, Haemophilus influenzae, Listeria monocytogenes), viruses (eg, herpes zoster), and fungi (eg, Aspergillus and Coccidioides species) [56-60].

Other associated conditions — For many patients with NASAH, diagnostic evaluation may not definitively identify the underlying cause. However, some conditions that have been associated with multiple forms of intracranial hemorrhage, including NASAH, may be attributed as the source of bleeding after excluding other causes. (See 'Diagnostic evaluation' below.)

●Sickle cell disease can be complicated by subarachnoid as well as intracerebral hemorrhage [5,8,61]. Most reported cases occur in children with an established diagnosis. These children are often found to have one or more aneurysms; in some cases, SAH is believed to result from fragile collateral blood vessels. Recent transfusion and treatment with glucocorticoids may be risk factors. (See "Acute stroke (ischemic and hemorrhagic) in children and adults with sickle cell disease", section on 'Intracranial hemorrhage management'.)

●Bleeding disorders can be complicated by NASAH. These include conditions such as disseminated intravascular coagulation or hemophilia and anticoagulant or thrombolytic therapy [3,8,29,62-65]. However, hematologic conditions more frequently present with subdural or intracerebral hemorrhage than with isolated NASAH. Patients with NASAH due to hematologic conditions frequently also present with evidence of systemic bleeding. However, extensive isolated NASAH attributed to reduced platelet activity has been reported in one case series [66]. In general, patients with isolated NASAH and an associated bleeding disorder should be evaluated for an underlying aneurysm or other vascular lesion. (See "Perimesencephalic nonaneurysmal subarachnoid hemorrhage".)

●Cocaine and other sympathomimetic substances have been associated with both aneurysmal SAH and NASAH [6,8,67-69]. The mechanism of bleeding in NASAH is not known but may be related to acute blood pressure surges and/or an underlying hypertensive or toxic vasculopathy [8,70]. Patients with SAH and cocaine abuse should be assumed to have an underlying aneurysm or other vascular lesion until proven otherwise. (See "Clinical manifestations, diagnosis, and management of the cardiovascular complications of cocaine abuse", section on 'Stroke'.)

CLINICAL PRESENTATION — The clinical presentation of NASAH varies by location and extent of the subarachnoid bleeding. Diffuse NASAH may mimic clinical features of aneurysmal SAH. Such patients frequently present with a sudden-onset severe (thunderclap) headache, sometimes associated with transient loss of consciousness, vomiting, or neck pain. (See "Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis", section on 'Clinical presentation'.)

Isolated SAH over the convexity may manifest with transient motor or sensory symptoms corresponding to underlying brain tissue. Symptoms may evolve over seconds to minutes, similar to focal epileptic phenomena and/or seizures [28]. (See "Cerebral amyloid angiopathy", section on 'Transient focal neurologic episodes'.)

DIAGNOSTIC EVALUATION — SAH should be considered in any patient complaining of a severe headache of sudden onset. Initial evaluation of patients suspected of having SAH includes urgent head CT [29]. If the CT scan fails to show blood in subarachnoid space, a lumbar puncture must be obtained. Additional details on the diagnosis of SAH are discussed separately. (See "Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis", section on 'Evaluation and diagnosis'.)

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.

Assess pattern of acute bleeding — The selection of initial imaging to identify the cause of bleeding generally varies by the distribution of SAH found on initial head CT (image 2 and algorithm 1).

●Aneurysmal SAH pattern – Aneurysmal SAH pattern located in the basal cisterns, in the Sylvian or interhemispheric fissures, or diffusely require initial angiographic evaluation to exclude a ruptured cerebral aneurysm as the cause of bleeding. Further testing is performed if angiographic evaluation has not identified an aneurysm or other vascular cause to bleeding. (See 'Evaluation for patients with aneurysmal pattern of bleeding' below.)

●Convexity SAH – SAH that is isolated to the convexities of the cerebral hemispheres may be due to one of several causes; the evaluation will vary by clinical circumstance. (See 'Evaluation for patients with isolated convexity SAH' below.)

Evaluation for patients with aneurysmal pattern of bleeding

Initial imaging — For patients with an aneurysmal SAH pattern, initial angiographic testing is performed to identify patients with a ruptured cerebral aneurysm as the cause of SAH. Patients with aneurysmal SAH typically require surgical or endovascular treatment and intensive medical care; The goal of such treatment is to reduce the risk of rebleeding and treat complications such as cerebral vasospasm and hydrocephalus; all of these are associated with significant morbidity and mortality. (See "Aneurysmal subarachnoid hemorrhage: Treatment and prognosis".)

Initial angiographic testing may also identify other vascular etiologies such as a vascular malformation or intracranial dissection. (See 'Etiologies' above.)

Cerebral angiography — Digital subtraction angiography (DSA) is the most sensitive and preferred imaging modality to assess for cerebral aneurysm. DSA should include demonstration of key arterial branch points, including the proximal posterior circulation, to effectively assess for cerebral aneurysms. In addition, injections of the external carotid and vertebral circulations and deep cervical branches may be helpful to identify other vascular causes such as a dural arteriovenous fistula or a vascular malformation in the cervical spine. (See "Aneurysmal subarachnoid hemorrhage: Clinical manifestations and diagnosis".)

Alternative options — Noninvasive testing with CT angiography (CTA) or magnetic resonance angiography (MRA) of the head may be used as an alternative initial angiographic test to identify suspected cerebral aneurysms or other vascular lesions. A major advantage of CTA over DSA is the speed and ease with which it can be obtained, often immediately after the diagnosis of SAH is made by head CT, when the patient is still in the scanner. In this setting, CTA is a more practical approach to acute diagnosis than MRA, given the constraints of acute patient management. Noninvasive testing may avoid the need for conventional angiography in some patients [71-73].

CTA may be more sensitive for aneurysm detection than MRA [74]. However, CTA or MRA has imperfect sensitivity for the detection of cerebral aneurysms, particularly small aneurysms [73]. Even when an aneurysm is identified by noninvasive techniques, DSA may also be performed to exclude multiple aneurysms and to plan surgical intervention [75].

Subsequent testing when cerebral angiography is negative — Additional testing to identify nonaneurysmal causes of bleeding should be performed when the underlying cause is uncertain despite initial angiographic evaluation.

Patients with perimesencephalic SAH — Additional imaging may be unnecessary for stable patients when initial DSA has excluded a cerebral aneurysm and the pattern of bleeding is consistent with a perimesencephalic SAH (image 3). Patients with a perimesencephalic pattern to SAH and a negative initial DSA have a low likelihood of having an aneurysmal cause of bleeding [2,76]. However, 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.

The imaging evaluation for perimesencephalic SAH is discussed in greater detail separately. (See "Perimesencephalic nonaneurysmal subarachnoid hemorrhage".)

Other patients — 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.

Magnetic resonance imaging — We perform gadolinium-enhanced magnetic resonance imaging (MRI) of the brain for patients with an uncertain cause to SAH after angiographic evaluation [6,32,77]. We also perform MRI of the spine for such patients with bleeding concentrated in the cervicomedullary regions. MRI with gadolinium may demonstrate angiographically occult lesions that can cause NASAH, including some vascular malformations in the brain or spinal cord, tumors (eg, pituitary adenoma), and intracranial arterial dissections [36,78]. Head and spinal CT with contrast can be performed as less sensitive alternative tests for patients unable to undergo MRI.

Delayed repeat brain MRI may be performed for selected patients after blood has resorbed (eg, six to eight weeks after SAH) if the initial study was limited by the presence and extent of acute bleeding.

The role of repeat cerebral angiography — For patients with an aneurysmal pattern SAH with an uncertain cause to symptoms despite initial cerebral DSA and MRI, we typically repeat DSA within 4 to 14 days after an initial negative study. However, the optimal timing of this study is unclear and should be individualized according to the patient's condition and presence of other complications. In reported case series, the repeat DSA has been performed at a follow-up interval between four days and four weeks [5,6,8,13,76,79-82].

Some patients with initial negative angiography are found to have an aneurysm on repeat angiography, at rates ranging from 3 to 24 percent in case series [5,6,8,13,76,83,84]. Rates as high as 49 percent have been reported for series of patients that exclude those with perimesencephalic NASAH and others with normal initial head CT [5,76,79]. 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.

A repeat study may also reveal an arterial dissection or a vascular malformation not identified on the initial study [33,34,85].

The value of additional angiographic testing to identify a cerebral aneurysm following two negative angiograms is uncertain [1,8,85]. We generally reserve further angiographic testing for patients with technically inadequate initial studies or if rebleeding occurs. Some older case series identified aneurysmal cause to SAH on a third angiogram or by surgical exploration [6,84], but others have reported no additional benefit with a third DSA [85]. While in some cases surgical exploration was prompted by an episode of rebleeding or a suspicious but nondiagnostic finding on angiography, in other cases it is not always certain why surgical exploration was performed.

Spinal angiography — Spinal angiography may be performed for some patients with NASAH and an unclear cause despite prior imaging [33-36]. This includes those with prominent back or neck pain, radicular or myelopathic features on examination, or abnormal but nondiagnostic findings on other neuroimaging studies. (See "Disorders affecting the spinal cord", section on 'Vascular malformations'.)

Evaluation for patients with isolated convexity SAH — Nontraumatic convexity SAH is associated with a diverse group of etiologies. These include:

●Cerebral amyloid angiopathy (see "Cerebral amyloid angiopathy")

●Reversible cerebral vasoconstriction syndrome (see "Reversible cerebral vasoconstriction syndrome")

●Cerebral venous thrombosis (see "Cerebral venous thrombosis: Etiology, clinical features, and diagnosis")

●Mycotic aneurysm from infective endocarditis (see "Overview of infected (mycotic) arterial aneurysm")

●Hemorrhagic cerebral tumor (see "Overview of the clinical features and diagnosis of brain tumors in adults")

●Intracranial dissection (see "Cerebral and cervical artery dissection: Clinical features and diagnosis")

●Vascular malformation (see "Vascular malformations of the central nervous system")

●Cerebral vasculitis (see "Primary angiitis of the central nervous system in adults")

The initial diagnostic imaging test to identify the underlying cause of isolated convexity SAH varies by clinical features (table 1). As examples, for an 80-year-old patient presenting with transient motor deficit and head CT showing acute convexity SAH, brain MRI with T2*-weighted susceptibility-weighted sequences may be performed as an initial diagnostic test to assess for cerebral amyloid angiopathy (CAA). For a patient presenting with multiple episodes of thunderclap headache over the preceding several days, CTA of the head may be performed to assess for reversible cerebral vasoconstriction syndrome (RCVS).

The causes of convexity SAH are typically nonaneurysmal [77,86,87]. However, angiographic evaluation to exclude ruptured cerebral aneurysm is warranted when SAH in the hemispheric convexities is accompanied by bleeding in the basal cisterns or Sylvian or interhemispheric fissures or is diffuse. In addition, angiographic evaluation may be warranted when the initial diagnostic imaging test does not identify the cause of convexity SAH. (See 'Initial imaging' above.)

MANAGEMENT AND PROGNOSIS — The approach to the general care and initial monitoring of patients with NASAH is the same as that for patients with aneurysmal SAH. Patients with extensive or diffuse NASAH may have a complicated course similar to patients with aneurysmal SAH, including risks of developing hydrocephalus or vasospasm [88]. However, other patients with NASAH presenting with a small amount of focal subarachnoid bleeding and mild symptoms may remain clinically stable and have a more benign course.

Supportive care — All patients with SAH should be admitted to a facility with neurologic and/or neurosurgical expertise to assess for underlying causes of bleeding and to monitor for complications of SAH. Patients with disabling neurologic symptoms such as hemiparesis or stupor or those with diffuse SAH should be admitted to an intensive care setting at a facility with neurologic and neurosurgical expertise to manage hemodynamic status and monitor for neurologic deterioration.

Specific acute supportive care strategies for patients with NASAH include blood pressure control, reversal of anticoagulation, deep venous thrombosis prophylaxis, and pain control. These issues are described in detail separately. (See "Aneurysmal subarachnoid hemorrhage: Treatment and prognosis", section on 'Acute care'.)

Complications — Patients with NASAH may develop complications associated with aneurysmal SAH [89]. These include:

●Rebleeding

●Vasospasm and cerebral ischemia

●Hydrocephalus

●Increased intracranial pressure

●Seizures

●Hyponatremia

●Cardiac abnormalities

There is little specific information about the incidence or severity of these complications in 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].

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." The Basics patient education pieces are written in plain language, at the 5^th to 6^th 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 sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading 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 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.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges David Brock, MD, CIP, who contributed to earlier versions of this topic review.