Subarachnoid Hemorrhage (SAH): Symptoms, Diagnosis, and Treatment

A subarachnoid hemorrhage (SAH) is a type of brain hemorrhage that occurs in the subarachnoid space. This space is located between the soft meninges (pia mater) and the arachnoid membrane (arachnoidea). It surrounds the brain and is normally filled with cerebrospinal fluid.

Subarachnoid hemorrhage must be distinguished from other types of cerebral hemorrhage, such as

• hemorrhages into the brain, known as cerebral parenchymal hemorrhages, as well as
• subdural and epidural hemorrhages, which occur in the area of the dura mater.

Women are affected by subarachnoid hemorrhage slightly more often than men, and the peak incidence occurs between the ages of 55 and 60. Subarachnoid hemorrhages occur in 8 to 9 people per 100,000 per year.

Overview of the brain’s location within the skull © 7activestudio | AdobeStock

Subarachnoid hemorrhages can be classified as either traumatic or non-traumatic.

Traumatic subarachnoid hemorrhages occur, for example, as a result of an accident. In such cases, small blood vessels in the subarachnoid space are damaged and bleed into this space. These hemorrhages are often located on the surface of the brain. Therefore, they are easily distinguished from non-traumatic subarachnoid hemorrhages.

In non-traumatic subarachnoid hemorrhages, no cause is found in approximately 15 percent of cases. However, in most cases—85 percent—a source of bleeding can be identified. Most commonly—in about 85 percent of cases—aneurysms are the cause.

Aneurysms as the Cause of a Subarachnoid Hemorrhage

Aneurysms are bulges in the cerebral arteries, also known as blood blisters. Under certain circumstances, they can rupture. Bleeding from an aneurysm usually occurs exclusively into the subarachnoid space. Less commonly, the cerebral parenchyma (functional brain tissue) is also affected, either in addition to or exclusively.

Aneurysms can be congenital and associated with certain conditions, such as polycystic kidney disease or

• connective tissue disorders such as Ehlers-Danlos syndrome,
• Marfan syndrome, or
• fibromuscular dysplasia (FMD)

.

Degenerative changes such as

• arteriosclerosis,
• smoking, and
• hypertension

can also contribute to the development of an aneurysm.

Aneurysms are found

• in 38 percent of cases—and thus most frequently—in the anterior cerebral artery (Arteria cerebri anterior), and there, most commonly at the junction of the two anterior cerebral arteries (Arteria or Ramus communicans anterior),
• in 28 percent of cases in the internal carotid artery (Arteria carotis interna),
• in 22 percent of cases in the middle cerebral artery (Arteria cerebri media),
• in approximately 8 percent of cases in the posterior circulation involving the basilar artery (Arteria basilaris).

A 38-year-old female patient with grade 2 SAH. The aneurysm in the right middle cerebral artery is marked with a thick arrow. 3D reconstructions and angiographic images before and after coil embolization.

Arteriovenous malformations as a cause of subarachnoid hemorrhage

Less common causes of subarachnoid hemorrhage include arteriovenous malformations such as

• dural AVF (arteriovenous fistula) or
• AVMs (arteriovenous malformations)

. These are abnormal connections between arteries and veins. In the case of fistulas, the connection occurs in the area of the dura mater, and in the case of AVMs, it occurs within the brain tissue.

These vascular malformations rarely bleed exclusively into the subarachnoid space. When they do, they also bleed into the brain tissue, where they cause parenchymal hemorrhage.

Other causes of subarachnoid hemorrhage

In rare cases, a subarachnoid hemorrhage can originate in the spinal cord. In such cases,

• tumors,
• vascular malformations, and
• aneurysms
• sinus and cerebral vein thromboses

are among the possible causes. Unlike aneurysmal hemorrhages, which are primarily located at the base of the skull, cerebral venous thromboses occur on the surface of the brain.

Cerebral hemorrhages account for approximately 15 to 20 percent of strokes. The symptoms of a stroke are varied and include:

• signs of paralysis,
• speech and vision problems,
• nausea and vomiting,
• seizures, and
• loss of consciousness.

An aneurysm-related subarachnoid hemorrhage is accompanied by loss of consciousness in 26 percent of cases. A non-aneurysm-related subarachnoid hemorrhage is associated with loss of consciousness in 2 to 4 percent of cases.

The main symptom of a subarachnoid hemorrhage is an acute and sudden, severe headache. Many patients describe it as an excruciating headache and compare it to a sudden thunderstorm with lightning and thunder. This headache differs significantly in intensity and nature from other known types of headaches.

CT (computed tomography) scan of the skull of a 54-year-old patient with SAH (subarachnoid hemorrhage). The hemorrhage is well-defined and localized only in front of the brainstem (arrow). In this prepontine hemorrhage, no source of bleeding is usually found, particularly not a ruptured aneurysm.

The diagnosis of a subarachnoid hemorrhage is usually made using computed tomography (CT). Fresh blood appears white on the scan. If no blood is detected on the CT scan and the patient has a clear-cut, severe headache, a cerebrospinal fluid (CSF) analysis is performed. This is done by puncturing the spinal canal at the level of the lumbar spine and can confirm or rule out a subarachnoid hemorrhage.

Magnetic resonance imaging (MRI) can also detect a subarachnoid hemorrhage. However, this can sometimes be very difficult in the case of a very recent subarachnoid hemorrhage. A CT scan of the head is therefore the standard diagnostic test.

Vascular Imaging to Diagnose a Subarachnoid Hemorrhage

If a subarachnoid hemorrhage (SAH) is clinically suspected, imaging must be performed promptly. This is usually a head CT scan.

If a subarachnoid hemorrhage is present, the physician must promptly identify the source of the bleeding. This can be done, for example, using CT angiography, which provides an early indication of whether an aneurysm is present.

Cranial CT and CT angiography with 3D reconstruction: A 38-year-old female patient with grade 2 SAH and evidence of a ruptured middle cerebral artery aneurysm on the right (arrows; middle cerebral artery) and a secondary aneurysm of the anterior cerebral artery (small arrow)

If the CT angiography is negative and thus inconclusive, conventional angiography (vascular imaging) is performed. It is significantly more accurate.

In this procedure, a catheter is inserted through a small, short plastic tube into one of the two femoral arteries. The physician then advances it into the arteries supplying the brain and can selectively visualize them from the neck.

A 45-year-old patient with an extensive, white-appearing subarachnoid hemorrhage (SAH) detected on computed tomography (CT) and evidence of a basilar artery aneurysm. The arrow marks the basilar artery aneurysm on the CT scan and the angiogram.

Following the vascular imaging, an interdisciplinary consultation with the neurosurgeons is initiated. In consultation with the specialists involved and the patient, an appropriate treatment plan can now be developed.

Treatment of a subarachnoid hemorrhage via the vascular system may offer advantages over open surgical repair using a vascular clip. An international study (the ISAT study) demonstrated this for certain aneurysms that had ruptured.

Consequently, in major centers with interventional neuroradiology and neurosurgery departments, 60–90 percent of ruptured cerebral aneurysms are treated via the vascular system. The procedures are performed under general anesthesia.

A tiny catheter is guided through the vascular system into the affected carotid artery. Using this catheter, the surgeon navigates a microcatheter coaxially into the aneurysm. The surgeon then typically fills the aneurysm from the inside using platinum coils.

Sometimes additional measures are necessary, such as the use of a stent (metal mesh or vascular prosthesis) or a balloon. Otherwise, the platinum coils could slip into the parent vessel and potentially occlude it.

When treating a subarachnoid hemorrhage with open surgery, the skull is opened (trepanation). The surgeon then locates the aneurysm under a microscope and clamps it off using a vascular clip while viewing it directly.

A cerebral aneurysm is a bulge in a cerebral artery © maniki | AdobeStock

Comorbidities that commonly occur as a result of a subarachnoid hemorrhage include:

• Hydrocephalus (“water on the brain”)
• Vasospasm (vascular spasms)

Hydrocephalus as a Comorbid Condition of a Subarachnoid Hemorrhage

Approximately 150 ml of cerebrospinal fluid (CSF) is produced daily. Due to the location of the hemorrhage, the CSF spaces become obstructed, preventing normal CSF circulation from occurring as usual.

The cerebrospinal fluid cannot reach the areas where it is reabsorbed by the blood vessels. As a result, the internal cerebrospinal fluid spaces expand, which can lead to hydrocephalus (“water on the brain”).

Such hydrocephalus is found in 50 to 55 percent of patients with aneurysm-related hemorrhage. It is treated acutely with a drainage tube inserted from outside the body. This method is known as external ventricular drainage (EVD). A plastic catheter placed in the lumbar spine region is also an option; this is referred to as lumbar drainage.

In cases of non-aneurysmal subarachnoid hemorrhage, the risk of requiring EVD placement is only 14 percent. After about two weeks, it is usually determined whether permanent drainage in the form of a shunt is necessary. The shunt typically diverts cerebrospinal fluid from the brain’s ventricles to the abdominal cavity; less commonly, it diverts it toward the heart.

Vasospasm (vascular spasms) as a Comorbid Condition of a Subarachnoid Hemorrhage

Vasospasms are responsible for the high mortality rate in the period following treatment for a subarachnoid hemorrhage. Vasospasms typically occur four days after the hemorrhage and last until days 10 to 12.

Vasospasms are caused by blood breakdown products. Treatment focuses primarily on improving cerebral blood flow. This can be achieved, among other things, by raising blood pressure—sometimes to excessive levels.

If all other measures fail, the affected vascular segments can be dilated locally—either mechanically or with medication—through the vascular system. Unfortunately, medication is usually only temporarily effective and may need to be repeated.

Sometimes a microcatheter is left in place to administer medication locally over a longer period of time. There are no reliable study data for any of these measures. However, these measures are only considered when the patient is at risk of suffering a major stroke, which could lead to severe neurological deficits or death.

A follow-up examination should be performed after surgical or endovascular aneurysm treatment following a subarachnoid hemorrhage.

Diagnostic angiography using a catheter remains the method that provides the highest level of detail. Depending on the findings, this procedure is performed once or multiple times. In most cases, it is performed once, approximately six months after the initial event.

At the same time, an examination using magnetic resonance imaging (MRI) and MR angiography is performed. The images obtained are compared with those from the conventional examination. They can also be used as a reference for future examinations.

These follow-up examinations are important for two reasons:

• to monitor the local findings for signs of recurrence (reappearance or growth of the original aneurysm), and
• to monitor the other brain vessels, since the risk of developing another aneurysm is approximately 9 to 10 percent.

In approximately 20 percent of patients with an aneurysm, another aneurysm can be detected right from the start. Often, multiple aneurysms occur simultaneously, which is why appropriate measures should be taken to confirm the diagnosis.

The likelihood of bleeding from a second, third, or subsequent aneurysm is also considered higher than that of an aneurysm that has not yet bled. Current recommendations (ISUIA study) state that an aneurysm should be treated if it is 7 mm or larger. This does not apply to secondary aneurysms, which should all be treated whenever possible due to the high probability of bleeding.

In 86 percent of our own patient cohort with ruptured aneurysms, the aneurysms were smaller than 7 mm. Therefore, when determining the indication for treatment of unruptured aneurysms, not only the size but also

• the morphology of the aneurysm,
• the patient’s comorbidities, and
• the patient’s age

be taken into account.

If an aneurysm is present, sports activities that lead to high blood pressure should be avoided. This also applies to short-term increases in intracranial pressure, such as straining during a bowel movement or lifting very heavy loads. Endurance sports that do not cause a significant rise in blood pressure are generally acceptable.

Very sharp increases in blood pressure can also occur during sexual intercourse, which is why patients frequently suffer a subarachnoid hemorrhage during sexual activity.

Flying in small aircraft should generally be avoided, as rapid changes in pressure could cause the aneurysm to rupture. Such high pressure differentials are unlikely in modern wide-body aircraft, so the risk in this case can certainly be considered low. In smaller aircraft, however, this does occur and should therefore be avoided.

Even today, a subarachnoid hemorrhage associated with an aneurysm still carries a high mortality rate of 40 to 50 percent. The probability of rebleeding is

• approximately 4 percent within the first 24 hours,
• 20 percent within 14 days, and
• 50 percent within one year.

Since every bleeding episode is associated with a high mortality rate, prompt treatment of the aneurysm should be sought. Treatment outcomes—for example, when the surgeon is fatigued—are associated with a higher complication rate. Therefore, procedures should only be performed at night under specific conditions.

About one-third of patients do not survive the initial hemorrhage. Approximately 15 percent die as a result of the subarachnoid hemorrhage and the treatment. However, the risk of death during treatment is only about 1 percent and is therefore of secondary concern.

About four days after a subarachnoid hemorrhage, patients develop vasospasms due to the breakdown products of the blood. These can lead to cerebral circulatory disorders resulting in strokes of varying severity.

Among survivors, approximately 50 percent of patients are left with varying degrees of disability. About 40 percent of these patients return to work.

What is a subarachnoid hemorrhage?

A subarachnoid hemorrhage is acute bleeding into the subarachnoid space between the pia mater and the brain. SAH is one of the most serious neurological conditions and is often caused by the rupture of an aneurysm or other arterial aneurysms.

What are the symptoms of a subarachnoid hemorrhage?

Typical symptoms of a subarachnoid hemorrhage include sudden, severe headaches, which are often described as the worst headaches a person has ever experienced. Additional symptoms include nausea and vomiting, headache, meningism, focal deficits, or altered consciousness.

How is the diagnosis made?

A subarachnoid hemorrhage is usually diagnosed using a CT (computed tomography) scan of the skull. If no clear hemorrhage is visible on the CT scan, MRI, lumbar puncture, and cerebrospinal fluid analysis are used. Angiography or other imaging techniques are also used to identify the source of the hemorrhage and the location of the aneurysm.

What treatments are available for a subarachnoid hemorrhage?

Treatment for a subarachnoid hemorrhage depends on the cause and extent of the hemorrhage. Aneurysms are often treated by coiling via a catheter or through surgical closure. Additionally, vasospasms, hydrocephalus, blood pressure issues, and other complications of a subarachnoid hemorrhage are treated.

What is the prognosis for a subarachnoid hemorrhage?

The prognosis for a subarachnoid hemorrhage depends on the extent of the bleeding, the speed of diagnosis and treatment, and any potential complications. Patients with a subarachnoid hemorrhage have an increased risk of rebleeding, especially in cases of aneurysmal subarachnoid hemorrhage. However, early treatment improves the prognosis and can reduce neurological damage.