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What Is a Subarachnoid Hemorrhage?
The meninges are three overlapping membranes that lie between:
- The structures of the central nervous system (the brain and spinal cord)
- The surrounding bone that encases and protects them (the skull and vertebral column, respectively)
These three protective membranes are named, from outermost to innermost:
- Dura mater, the outermost of the three meninges, forming a tough, protective outer layer
- Arachnoid mater, the intermediate meningeal layer, named for its delicate, web-like (spider-like) appearance
- Pia mater, the innermost meningeal layer, which makes direct contact with the surface of the brain and spinal cord, closely following every contour and fold
The spaces defined by these three membranes are correspondingly named:
- The epidural space, located between the dura mater and the surrounding bony structures
- The subdural space, located between the dura mater and the arachnoid mater
- The subarachnoid space, located between the arachnoid mater and the pia mater
A subarachnoid hemorrhage (SAH) refers specifically to the presence of blood within this subarachnoid space, meaning the space located between the arachnoid mater and the pia mater, an area that normally contains only cerebrospinal fluid rather than blood.
The origin of this bleeding can be:
- Spontaneous, occurring without any preceding injury
- Secondary to head trauma, resulting from an external injury to the head
Regardless of the underlying cause, subarachnoid hemorrhage constitutes, in every single case, a genuine medical emergency. If not promptly recognized and treated, this condition can lead to the development of severe, permanent disability, and in many cases, can prove fatal.
According to Harvard Health, many patients who experience a subarachnoid hemorrhage unfortunately do not survive long enough to even reach a hospital. Among those who do manage to receive prompt medical attention, the overall prognosis depends heavily on the severity of the initial brain injury. If the patient remains awake and alert, without evidence of neurological deficits, the immediate prognosis tends to be relatively favorable, though it must be emphasized that the patient’s condition can unfortunately deteriorate rapidly and unpredictably at any moment during the critical early period following the bleed.
Causes
Setting aside traumatic head injury, which is generally considered a distinct category in its own right, the single most common cause of subarachnoid hemorrhage overall, accounting for approximately 85 percent of all cases, is the rupture of a cerebral aneurysm, meaning an abnormal dilation or bulging of an artery that leads to progressive weakening of the vessel wall at that specific point.
Among the risk factors known to increase the likelihood of aneurysm rupture are:
- High blood pressure (hypertension)
- Smoking
- Family history of aneurysm or subarachnoid hemorrhage
- Alcoholism
- Cocaine use
Other Medical Causes
Among the other possible medical causes of subarachnoid hemorrhage, we should mention:
- Rupture of arteriovenous malformations, meaning abnormalities of the intracerebral circulation present since birth, consisting of a tangled cluster of dilated blood vessels whose walls are notably fragile and prone to rupture
- Brain tumors, which can occasionally invade or erode blood vessels, leading to hemorrhage
- Vasculitis, an inflammatory condition affecting blood vessel walls that can weaken them and predispose to rupture
Subarachnoid hemorrhage can also be associated with:
- Abuse of cocaine and other illicit substances, which can cause sudden, severe spikes in blood pressure
- Sickle cell anemia, a genetic blood disorder associated with various vascular complications
Understanding Cerebral Aneurysms
Given that aneurysm rupture represents the overwhelming majority of spontaneous subarachnoid hemorrhage cases, it is worth understanding a bit more about these vascular abnormalities. A cerebral aneurysm develops when a weak spot in the wall of a brain artery balloons outward, similar to a thin spot on an overinflated balloon. Many people live their entire lives with an unruptured cerebral aneurysm without ever knowing it exists, since small aneurysms often produce no symptoms whatsoever until the moment of rupture. Aneurysms are sometimes discovered incidentally during imaging performed for unrelated reasons, and when identified before rupture, they can often be treated proactively to prevent this potentially catastrophic event from ever occurring.
Symptoms
In many cases, there are no warning symptoms whatsoever that might foreshadow the impending severity of the situation. Spontaneous rupture of blood vessels can be triggered by even relatively minor physical exertion, such as a bout of coughing, straining during a bowel movement, lifting a heavy object, or sexual activity, activities that momentarily raise blood pressure within the vessels of the brain.
The classic, hallmark symptom of subarachnoid hemorrhage is what is medically termed a “thunderclap headache”, meaning a headache frequently described by patients as “the worst headache of my life”. This headache characteristically develops and intensifies exponentially within a matter of seconds to minutes, and is often perceived and described by patients as a throbbing sensation localized to the back of the head (the occipital region).
In approximately one-third of affected individuals, this thunderclap headache remains the only symptom present. Other patients, however, may go on to develop:
- Vomiting
- Seizures and epileptic episodes
- Alterations in level of consciousness, ranging from lightheadedness, to fainting, all the way to coma in the most severe cases
- Neck stiffness, a classic finding resulting from irritation of the meninges by blood
- Visual disturbances, including photophobia (light sensitivity) and double vision
In response to the hemorrhage, the body produces large quantities of adrenaline (epinephrine), which results in a significant increase in cardiac pressure. This surge can lead to:
- Alterations in heart rate, including both dangerously fast and dangerously slow rhythms
- Alterations in respiratory rate and breathing pattern
Serious neurological complications can also develop, and these can unfortunately become irreversible within a remarkably short period of time, sometimes just minutes to hours following the initial bleed, underscoring the critical importance of rapid recognition and treatment.
Fever, headache, and confusion are all very common symptoms that can persist, particularly during the first 5 to 10 days following the hemorrhage, and in many cases, these symptoms continue for considerably longer as the brain and body work to recover from this significant insult.
Complications
Subarachnoid hemorrhage can lead to the development of several serious complications, each requiring careful monitoring and, in many cases, specific targeted treatment:
Hydrocephalus
Blood within the subarachnoid space can coagulate and subsequently obstruct the normal drainage pathways of cerebrospinal fluid. This resulting accumulation of blood and cerebrospinal fluid within the confined space of the skull causes intracranial pressure to rise progressively. Hydrocephalus typically manifests with:
- Headache
- Drowsiness
- Nausea and vomiting
Vasospasm
Vasospasm refers to a rapid, sustained contraction of the blood vessel wall that obstructs normal blood flow and can lead to an ischemic stroke if severe enough to significantly reduce blood supply to brain tissue. Vasospasm typically manifests with:
- Weakness affecting one side of the body
- Loss of sensation affecting one side of the body
- Difficulty with speech or language
Chemical Meningitis
This complication results from the irritating effect that blood itself has upon direct contact with sensitive brain tissue and the meninges, producing an inflammatory response similar to that seen in infectious meningitis, though without an actual infectious cause.
Timing of Complications
The risk of developing cerebral edema (fluid accumulation within brain tissue) and vasospasm, with its associated risk of ischemic stroke resulting from reduced blood flow to this extraordinarily delicate organ, reaches its peak between approximately 72 hours and 10 days following the onset of the initial hemorrhage. A second, subsequent hemorrhage (rebleeding), when it occurs, most commonly develops within approximately the first 7 days following the initial bleed, which is precisely why close hospital monitoring during this critical window is so essential.
Long-Term Complications
Beyond these acute complications, several long-term complications can also develop following subarachnoid hemorrhage, including:
- Epilepsy, resulting from scarring or irritation of brain tissue
- Memory problems, along with difficulties with attention and concentration
- Mood changes and disorders, including the development of depression, which is remarkably common among survivors of subarachnoid hemorrhage and deserves proactive screening and treatment during recovery
Diagnosis
The diagnosis of subarachnoid hemorrhage is generally suspected based on the characteristic symptoms described above, but is confirmed through specific diagnostic imaging and testing. The most common diagnostic procedures include:
CT Scan
A CT scan of the brain, performed without contrast material, represents the first-line diagnostic test and allows physicians to visualize blood occupying the cerebral cisterns, specific fluid-filled spaces within the subarachnoid space. This distinctive pattern occurs because the pia mater closely follows the anatomical contours of the brain, intimately covering it and following it even into its deepest grooves and folds, whereas the arachnoid mater, along with the pia mater in certain regions, passes over these same contours more like a bridge, without following every fold precisely. This differing relationship between the membranes means that in certain locations, the pia mater separates somewhat from the arachnoid mater, creating natural cistern spaces where blood characteristically tends to accumulate and become visible on imaging.
Angiography and CT Angiography
Angiography, including CT angiography, allows physicians to precisely identify the specific source and location of the hemorrhage, most critically whether an aneurysm is present and exactly where it is located. This procedure is performed by inserting a catheter into an artery, typically in the groin or wrist, and carefully advancing it through the vascular system until it reaches the cerebral circulation. At this point, contrast material is injected directly into the blood vessels, and detailed radiographic images are then acquired, allowing detailed visualization of the brain’s blood vessels and any abnormalities present.
Lumbar Puncture (Spinal Tap)
A lumbar puncture, also known as a spinal tap, can be performed to detect the presence of blood within the cerebrospinal fluid, and is particularly useful in cases where the initial CT scan appears normal despite a strong clinical suspicion of subarachnoid hemorrhage, since a small hemorrhage can occasionally be missed on CT imaging, especially if some time has passed since the initial bleed.
The procedure is performed with the patient positioned on their side with their back curved forward (in a fetal position), and the needle is inserted into the space between the fourth and fifth lumbar vertebrae, well below the level where the spinal cord itself ends, making this a very safe procedure when performed correctly. Following the procedure, the patient is generally asked to remain lying flat for a couple of hours and to drink plenty of fluids, both measures aimed at reducing the risk of a post-procedure headache.
The Critical Importance of Timely Diagnosis
The speed and accuracy with which subarachnoid hemorrhage is diagnosed can have a particularly significant impact on the patient’s overall prognosis. Because thunderclap headache can occasionally be dismissed, either by patients themselves or in clinical settings, as a severe but ultimately benign headache such as a migraine, maintaining a high index of suspicion for this potentially catastrophic diagnosis whenever a patient presents with a sudden, unusually severe headache is absolutely essential for ensuring timely, life-saving treatment.
Treatment and Therapy
Subarachnoid hemorrhage represents a genuine medical emergency requiring immediate, specialized hospital care, ideally at a facility equipped with neurosurgical and neurocritical care capabilities. Upon admission, the patient will be kept under conditions of complete rest, and any ongoing anticoagulant or antiplatelet medications will be immediately discontinued, given the obvious risk these medications pose in the setting of active bleeding.
Initial treatment typically involves the use of medications aimed at alleviating the severe headache, generally utilizing pain relievers such as opioids, which, importantly, do not have any adverse effect on blood clotting, unlike certain other pain medications that might otherwise be considered.
Any developing complications will be actively treated and, whenever possible, proactively prevented through careful monitoring, while arterial hypertension (high blood pressure) is generally only actively treated if it becomes very significantly elevated, since some degree of elevated blood pressure may actually be necessary to maintain adequate blood flow to the brain during this critical period.
Definitive Treatment of the Underlying Cause
Depending on the specific underlying cause identified, surgical intervention or interventional radiology procedures may be considered, and in certain cases, such as a ruptured cerebral aneurysm, definitive treatment of the underlying vascular abnormality becomes absolutely essential to prevent potentially fatal rebleeding. Two main approaches are generally used for treating a ruptured cerebral aneurysm:
- Surgical clipping: a neurosurgical procedure in which a small metal clip is placed directly across the neck of the aneurysm, effectively sealing it off from normal blood circulation and preventing further bleeding
- Endovascular coiling: a minimally invasive procedure performed through the blood vessels themselves, in which small platinum coils are carefully placed within the aneurysm sac, promoting clotting within the aneurysm and effectively excluding it from the normal circulation
The choice between these two approaches depends on numerous factors, including the specific size, shape, and location of the aneurysm, as well as the patient’s overall clinical condition, and is generally made collaboratively by a specialized team including neurosurgeons and interventional neuroradiologists.
Managing Vasospasm
Given the significant risk of vasospasm during the days following hemorrhage, patients are often treated prophylactically with medications such as nimodipine, a calcium channel blocker that has specifically been shown to improve neurological outcomes in patients with subarachnoid hemorrhage, likely by helping to prevent or reduce the severity of vasospasm-related complications. Close monitoring for early signs of vasospasm, often using specialized ultrasound techniques or repeat angiography, allows for prompt intervention if this complication begins to develop.
Recovery and Long-Term Outlook
Even in relatively milder cases, recovery from subarachnoid hemorrhage can prove to be a slow and often genuinely frustrating process. During this recovery period, it is common for patients to experience ongoing difficulties with:
- Easy fatigability, feeling exhausted with even modest physical or mental exertion
- Persistent headaches, which may continue for weeks to months following the acute event
- Sleep disturbances, including both difficulty falling asleep and disrupted, non-restorative sleep
Rehabilitation following subarachnoid hemorrhage often requires a comprehensive, multidisciplinary approach, potentially involving physical therapy to address any motor deficits, occupational therapy to help patients regain independence with daily activities, speech and language therapy if communication has been affected, and neuropsychological support to address cognitive changes and the emotional impact of surviving such a serious medical event.
Given the well-documented risk of developing depression following subarachnoid hemorrhage, ongoing psychological support and, when appropriate, treatment for mood disorders should be considered an integral part of the overall recovery process, rather than an afterthought. Family members and caregivers also frequently benefit from support and education throughout this recovery journey, as caring for a loved one recovering from a serious brain injury can itself be emotionally and practically demanding.
Recovery timelines vary enormously from patient to patient, depending on the severity of the initial hemorrhage, the presence and severity of any complications, and individual patient factors. While some patients experience a relatively complete recovery within months, others may face lasting cognitive, physical, or emotional challenges that require ongoing management and support well beyond the initial hospitalization.
Frequently Asked Questions
Is every severe headache a sign of subarachnoid hemorrhage?
No, certainly not. The vast majority of even quite severe headaches, including migraines, are not caused by subarachnoid hemorrhage. However, the specific combination of a sudden, explosive onset reaching maximum intensity within seconds to minutes, genuinely described as “the worst headache of my life”, warrants immediate emergency medical evaluation to definitively rule out this potentially life-threatening cause.
Can a cerebral aneurysm be detected before it ruptures?
Yes, unruptured cerebral aneurysms can sometimes be detected through imaging studies such as CT angiography or MRI angiography, particularly when these studies are performed for unrelated reasons or as part of screening in individuals with a strong family history of aneurysms. When identified before rupture, treatment options exist to secure the aneurysm and prevent future rupture.
What are the survival rates for subarachnoid hemorrhage?
Subarachnoid hemorrhage carries a significant risk of mortality, with a substantial proportion of patients not surviving to reach the hospital. Among those who do receive prompt medical care, survival rates have improved considerably over recent decades due to advances in neurocritical care and treatment techniques, though outcomes remain highly dependent on the severity of the initial bleed and how quickly treatment is received.
Can subarachnoid hemorrhage happen to young, healthy people?
Yes, although the risk increases with age and with the presence of specific risk factors such as smoking, high blood pressure, and family history, subarachnoid hemorrhage, particularly when caused by rupture of a congenital arteriovenous malformation or aneurysm, can occur in relatively young, otherwise healthy individuals with no prior warning.
Is it safe to fly or travel after having a subarachnoid hemorrhage?
This depends entirely on the individual patient’s specific situation, including how much time has passed since the hemorrhage, whether the underlying cause has been definitively treated, and whether any ongoing complications are present. This decision should always be made in close consultation with the treating neurologist or neurosurgeon before any travel plans are finalized.
Can subarachnoid hemorrhage recur after successful treatment?
Once the underlying cause, such as a ruptured aneurysm, has been definitively treated through clipping or coiling, the risk of recurrence from that specific source is generally low. However, patients who have experienced one aneurysm may have a somewhat increased risk of developing additional aneurysms over time, which is why ongoing monitoring is often recommended by the treating specialist.
Sources and Bibliography
- Macdonald, R.L., Schweizer, T.A. Spontaneous Subarachnoid Haemorrhage. The New England Journal of Medicine. NEJM: Subarachnoid Hemorrhage
- Harvard Health Publishing: Subarachnoid Hemorrhage
- MSD Manual (Merck Manual): Subarachnoid Hemorrhage
- American Stroke Association: Subarachnoid Hemorrhage
- National Institute of Neurological Disorders and Stroke (NINDS): Cerebral Aneurysms
- Mayo Clinic: Brain Aneurysm
