In short
Diagnosing a subarachnoid haemorrhage requires quick action and specialized imaging tests, as this is a medical emergency where every minute counts. The most common sign is a sudden, extremely severe headache, often called a "thunderclap headache," which prompts doctors to investigate whether bleeding has occurred in the space around the brain.
Key points
- A thunderclap headache—sudden, severe, and unlike any headache you've had before—is the hallmark symptom of subarachnoid haemorrhage and requires immediate emergency care.
- The first diagnostic test is usually a CT scan of the head, which is highly effective at detecting bleeding when done within the first 24 to 48 hours.
- If the CT scan does not show bleeding but doctors still suspect it, a lumbar puncture (spinal tap) is performed to check for blood in the cerebrospinal fluid.
- A CT angiogram, MR angiogram, or cerebral angiography is used to locate the source of bleeding, most often a ruptured brain aneurysm.
- About 10 to 15 percent of people with a subarachnoid haemorrhage die before reaching the hospital, making rapid recognition and emergency response critical.
- A sentinel headache—a smaller bleed that causes a severe headache that improves—can be a warning sign, and ignoring it increases the risk of a second, more severe haemorrhage within a week.
- Approximately 80 to 85 percent of subarachnoid haemorrhages are caused by a ruptured brain aneurysm, and about 3 to 5 percent of the general population has an unruptured aneurysm without knowing it.
- Recovery from subarachnoid haemorrhage varies widely, with some people recovering fully and others experiencing lasting problems with memory, concentration, mood, and physical function.
Introduction: When to Seek Diagnostics
If you experience a sudden, extremely painful headache that comes on like a clap of thunder, you need to seek medical help immediately. This type of headache, often described as "the worst headache of my life," is the hallmark symptom of a subarachnoid haemorrhage, which is bleeding in the space between the brain and the protective tissues that cover it. This condition is a medical emergency, and getting the right diagnosis quickly can be the difference between life and death.
People who should undergo diagnostic testing include anyone experiencing this thunderclap headache, especially when it is accompanied by other warning signs. These may include nausea and vomiting, a stiff neck, sensitivity to light, confusion, sudden weakness, or even loss of consciousness. The headache typically starts within a split second and becomes intensely painful right away, unlike other headaches that build up gradually over time.
Sometimes a person may experience a smaller bleed first, which can cause a severe headache that improves on its own. This is called a sentinel headache and it acts as a critical warning sign. People who ignore this warning and do not get medical treatment are at high risk of having a second, more severe haemorrhage within the next week. This is why it is so important to take any sudden, severe headache seriously and seek emergency evaluation, even if the symptoms seem to get better.
Anyone who has risk factors for this condition should be especially vigilant. Risk factors include having a known brain aneurysm (a bulge in a blood vessel in the brain), a family history of aneurysms, high blood pressure, smoking, or using drugs like cocaine or methamphetamine. People with certain genetic conditions, such as polycystic kidney disease or connective tissue disorders like Ehlers-Danlos syndrome, are also at higher risk. Head injuries can also cause subarachnoid bleeding, so anyone who has hit their head hard and then develops a severe headache should be evaluated urgently.
Diagnostic Methods to Identify the Condition
When you arrive at the emergency room with symptoms suggesting a subarachnoid haemorrhage, doctors need to confirm the diagnosis quickly. The first and most important test is a CT scan, also called computed tomography, of the head. This imaging test is very effective at detecting bleeding in the brain, especially if it is performed soon after the symptoms begin. The CT scan does not require any injections or invasive procedures for the initial images. It takes cross-sectional pictures of your brain and can show if blood has leaked into the space around it.
The CT scan works best when done within the first 24 to 48 hours after the headache starts, as the blood is most visible during this time. However, if you have a low red blood cell count or if the amount of bleeding is very small, the CT scan might not detect it. In these cases, doctors may need to perform additional tests to confirm the diagnosis.
If the CT scan does not clearly show bleeding but doctors still strongly suspect a subarachnoid haemorrhage based on your symptoms, they may perform a lumbar puncture, also called a spinal tap. During this procedure, a needle is inserted into your lower back to collect a small sample of the fluid that surrounds your brain and spinal cord, known as cerebrospinal fluid. This fluid is then examined in a laboratory to look for traces of blood or breakdown products from blood that might not have shown up on the CT scan. The presence of blood in the cerebrospinal fluid is a strong indication that a haemorrhage has occurred.
Once bleeding is confirmed, the next step is to find out where the bleeding came from and what caused it. In most cases, about 80 to 85 percent of subarachnoid haemorrhages are caused by a ruptured brain aneurysm, which is a bulge in the wall of a blood vessel in the brain. To locate the aneurysm, doctors use specialized imaging tests that allow them to see the blood vessels in detail.
A CT angiogram is often the next test performed. This is a CT scan with a contrast dye injected into a vein, which makes the blood vessels visible on the images. The dye travels through your bloodstream and highlights the arteries and veins in your brain, allowing doctors to see if there is an aneurysm or another vascular abnormality, such as an arteriovenous malformation (a tangled cluster of blood vessels). The CT angiogram is quick and non-invasive, making it a useful tool in emergency situations.
Another imaging option is an MRI scan, or magnetic resonance imaging, which uses magnets and radio waves instead of X-rays to create detailed images of the brain. An MRI can sometimes detect bleeding that a CT scan misses, especially in rare cases or when the bleeding is very small. Similar to the CT angiogram, an MR angiogram can be done with a contrast dye to visualize the blood vessels more clearly.
In some situations, doctors may need to perform a cerebral angiography, which is considered the gold standard for identifying the source of bleeding. This procedure involves inserting a thin, flexible tube called a catheter into an artery, usually in the groin, and guiding it up to the blood vessels in the brain. A contrast dye is then injected through the catheter, and X-ray images are taken to create detailed pictures of the brain's blood vessels. This test provides the most accurate information about the location, size, and shape of an aneurysm or other vascular problem. Although it is more invasive than a CT or MRI, it is often necessary to plan the best treatment.
Sometimes, the initial angiography does not reveal an aneurysm, even though bleeding has been confirmed. In these cases, doctors may recommend a second angiogram after a few days or weeks, as some aneurysms can be difficult to see at first due to swelling or spasm in the blood vessels. About 15 to 20 percent of people with a confirmed subarachnoid haemorrhage do not have a visible vascular lesion on the first imaging study.
In addition to imaging tests, doctors will perform a detailed physical examination and neurological assessment. They will check your alertness, ability to move your limbs, speech, vision, and reflexes. The results of this examination help doctors determine the severity of the haemorrhage and predict your chances of recovery. There are grading scales used by doctors to classify how serious the bleeding is and how much it has affected your brain function. The presence of neurological deficits, such as weakness on one side of the body or difficulty speaking, indicates a higher grade of haemorrhage and a more guarded outlook.
Other diagnostic tests may include blood tests and an electrocardiogram (ECG) to check your heart rhythm. Subarachnoid haemorrhage can sometimes cause changes in the heart and lungs, so doctors need to monitor these systems closely. Blood pressure monitoring is also crucial, as high blood pressure increases the risk of further bleeding before the aneurysm can be treated.
Diagnostics for Clinical Trial Qualification
Information about specific diagnostic tests and methods used as standard criteria for enrolling patients in clinical trials for subarachnoid haemorrhage was not provided in the sources. Clinical trials may have their own inclusion and exclusion criteria based on the severity of the haemorrhage, the presence of an aneurysm, the patient's overall health, and other factors, but these details were not available in the materials reviewed.
Prognosis and Survival Rate
Prognosis
The outlook after a subarachnoid haemorrhage varies greatly from person to person and depends on several factors, including where in the brain the bleeding occurred, how much blood was released, and how quickly treatment was started. The prognosis is also influenced by the person's age, overall health, and the severity of neurological damage at the time of the initial bleed. People who have a high-grade haemorrhage, meaning they are in a coma or have severe neurological deficits, generally face a more guarded prognosis, although the coma can sometimes be reversible with prompt treatment.
Subarachnoid haemorrhage can lead to permanent brain damage, mental and physical disability, and a significant impact on quality of life. Common long-term effects include problems with memory, concentration, and communication, as well as mood changes, depression, fatigue, and seizures. Some people also experience heart, lung, or liver problems as complications of the haemorrhage. Recovery can take months or even years, and while most people improve with treatment and rehabilitation, not everyone returns to their previous level of function. Some people recover fully, but others are left with lasting impairments.
The risk of further complications, such as a second bleed, blood vessel spasm (vasospasm), or a build-up of fluid around the brain (hydrocephalus), also affects the prognosis. Early treatment to secure the aneurysm and prevent rebleeding is critical to improving outcomes. People who survive the initial event and receive prompt, comprehensive care in a specialized neurosciences unit have the best chance of recovery.
Survival rate
Subarachnoid haemorrhage is a life-threatening condition with high mortality rates. About 10 to 15 percent of people die before they reach the hospital. Among those who make it to medical care, approximately 40 percent die within one month of the bleeding event. Overall, mortality rates have declined over the past few decades due to advances in neurosurgery, imaging technology, and intensive care, but the condition remains very serious.
The annual incidence of subarachnoid haemorrhage in the United States is estimated at 6 to 11 cases per 100,000 people, which corresponds to roughly 30,000 cases each year. Globally, the incidence is about 8 to 9 per 100,000 people, with around 700,000 new cases and 350,000 deaths reported in 2021. The burden of the disease is highest in Finland and Japan, where the incidence can be as high as 15 to 25 per 100,000 people. Women are more commonly affected than men, and the condition most often strikes people between the ages of 40 and 60.
Survival and recovery depend heavily on the speed and quality of medical care received. People who survive the first few critical days and weeks still face a long road to recovery, with ongoing risks of secondary complications and long-term disability. However, with modern treatment approaches, including early aneurysm repair and aggressive management of complications, outcomes have improved significantly compared to decades past.
