Subarachnoid hemorrhage (SAH) is a form of cerebral hemorrhage that occurs in the subarachnoid space. This space lies between the soft meninges(pia mater) and thearachnoid membrane(arachnoid membrane). It surrounds the brain and is normally filled with cerebrospinal fluid.
Other cerebral hemorrhages must be distinguished from subarachnoid hemorrhage, such as
- Bleeding into the brain, so-called cerebral pararechymal hemorrhages and
- subdural and epidural hemorrhages that occur in the area of the hard meninges (dura mater).
Women are slightly more frequently affected by subarachnoid hemorrhage than men and the peak age is 55 to 60 years.
Subarachnoid hemorrhages occur in 8 to 9 people per 100,000 people per year.
Overview of the location of the brain in the skull © 7activestudio | AdobeStock
A subarachnoid haemorrhage can be divided into traumatic and non-traumatic haemorrhages.
Traumatic subarachnoid hemorrhages occur, for example, in the context of an accident. Small vessels in the subarachnoid space are injured and bleed into this space. These hemorrhages are often located on the surface of the brain. They are therefore easy to distinguish from non-traumatic subarachnoid haemorrhages.
In about 15 percent of cases of non-traumatic subarachnoid hemorrhage, no cause is found. However, in 85 percent of cases, a source of bleeding can usually be identified. Aneurysms are the most common cause, in around 85 percent of cases.
Aneurysms as the cause of a subarachnoid haemorrhage
Aneurysms are bulges in the cerebral arteries, also known as blood blisters. They can burst under certain circumstances. The aneurysm hemorrhage usually occurs exclusively in the subarachnoid space. More rarely, the brain parenchyma (functional tissue of the brain) is also or exclusively affected.
Aneurysms can be congenital and associated with certain diseases, such as polycystic kidney disease or
- connective tissue diseases such as Ehlers-Danlos disease,
- Marfan syndrome or
- fibromuscular dysplasia (FMD)
occur together.
Degenerative changes such as
can also promote the development of an aneurysm.
Aneurysms are found
- in 38 percent of cases and thus most frequently in the anteriorcerebral artery (arteria cerebri anterior) and there again most frequently at the junction of the two anterior cerebral arteries(arteria or ramus communicans anterior),
- in 28 percent of cases in the internalcarotid artery (arteria carotis interna),
- in 22 percent of cases in the middle cerebralartery (arteria cerebri media),
- in approx. 8 percent of cases in the posterior circulation with the brainstemartery (basilar artery).
38-year-old female patient with SAB HH grade 2. The aneurysm on the middle cerebral artery on the right is marked with a thick arrow. 3D reconstructions and angiographic images before and after coliembolization.
Arteriovenous vascular malformations as a cause of subarachnoid hemorrhage
Rarer causes of subarachnoid hemorrhage can be arteriovenous vascular malformations such as
- dural AVF (arteriovenous fistula) or
- AVM (arteriovenous malformation)
can be. These are short-circuit connections between arteries and veins; in the case of fistulas, the short circuit is in the area of the hard meninges and in the case of AVMs within the brain tissue.
These vascular malformations rarely bleed only into the subarachnoid space. If they do, then they also bleed into the brain tissue, where they cause a parenchymal hemorrhage.
Other causes of a subarachnoid hemorrhage
Rarely, a subarachnoid hemorrhage can originate from the spinal cord of the spinal column. Here are
- Tumors,
- vascular malformations and
- aneurysms
- sinus and cerebral vein thromboses
as possible causes. In contrast to aneurysm hemorrhages, which are concentrated at the base of the skull, cerebral vein thromboses are located on the surface of the brain.
Cerebral hemorrhages are responsible for around 15 to 20 percent of strokes. Symptoms of a stroke are varied and include
- Symptoms of paralysis,
- Speech and visual disturbances,
- nausea and vomiting,
- seizures and
- loss of consciousness.
Aneurysm-related subarachnoid hemorrhage is accompanied by loss of consciousness in 26 percent of cases. Non-aneurysm-related subarachnoid hemorrhage is associated with loss of consciousness in 2 to 4 percent of cases.
The main symptom of subarachnoid hemorrhage is an acute and sudden massive headache. It is described by many sufferers as an annihilation headache and compared to a sudden thunderstorm with lightning and thunder. This headache differs considerably in intensity and pain character from other known headaches.
ACT (computed tomography) of the skull of a 54-year-old patient with SAB (subarachnoid hemorrhage). The hemorrhage is circumscribed and localized only in front of the brain stem (arrow). In this prepontine hemorrhage, no source of bleeding is usually found, especially not a ruptured aneurysm.
The diagnosis of a subarachnoid hemorrhage is usually made with the aid of computer tomography (CT). Fresh blood appears white. If no blood can be detected in the CT scan and there is a verifiable annihilation headache, a cerebrospinal fluid examination is performed. This is carried out by puncturing the spinal canal at the level of the lumbar spine and can detect or rule out a subarachnoid haemorrhage.
A magnetic resonance imaging(MRI) scan can also detect a subarachnoid hemorrhage. However, this can sometimes be very difficult in the case of a very recent subarachnoid haemorrhage. A CT scan of the head is therefore the standard examination.
Vascular imaging to clarify a subarachnoid haemorrhage
If there is a clinical suspicion of subarachnoid haemorrhage (SAH), an imaging clarification must be carried out promptly. This is usually a cranial CT scan.
If a subarachnoid hemorrhage is present, the doctor must identify the source of the bleeding promptly. This is possible by means of CT angiography, for example, and provides an early indication of whether an aneurysm can be detected.
ACT of the skull and CT angiography with 3D reconstruction: 38-year-old female patient with grade 2 SAB HH and evidence of a hemorrhaged media aneurysm on the right (arrows, media = middle cerebral artery) and a secondary aneurysm of the anterior cerebral artery (anterior cerebral artery, small arrow)
If the CT angiography is negative and therefore inconclusive, conventional angiography (vascular imaging) is used. It is much more accurate.
A catheter is inserted into one of the two inguinal arteries via a small, short plastic tube. The doctor then pushes it into the arteries supplying the cerebral vessels and can selectively visualize these from the neck.
A45-year-old patient with extensive white SAB and evidence of a basilar artery head aneurysm on computed tomography (CT). The arrow marks the basilar artery head aneurysm on CT and angiography.
Following the vascular imaging, an interdisciplinary discussion is sought with the neurosurgeons. A suitable therapy can now be developed in consultation with the specialists involved and the patient.
Treating a subarachnoid hemorrhage through the vascular system can have advantages over open surgical treatment with a vascular clip. An international study (ISAT study) was able to prove this in certain aneurysms that had hemorrhaged.
Therefore, in large centers with interventional neuroradiology and neurosurgery, 60 - 90 percent of hemorrhaged brain aneurysms are treated through the vascular system. Treatments are carried out under general anesthesia.
A tiny catheter is inserted into the affected carotid artery via the vascular system. The surgeon then navigates a microcatheter coaxially into the aneurysm. He then plugs the aneurysm from the inside, usually using platinum coils.
Sometimes additional measures are necessary with the aid of a stent (metal mesh or vascular prosthesis) or balloons. Otherwise, the platinum coils could, for example, prolapse into the carrier vessel, which may then become blocked.
When treating a subarachnoid hemorrhage through open surgery, the skull bone is opened (trepanation). The surgeon then locates the aneurysm under the microscope and removes it with a vascular clip under visualization.
A brain aneurysm is a bulge in a cerebral artery © maniki | AdobeStock
Concomitant diseases that regularly occur as a result of subarachnoid hemorrhage are
Hydrocephalus as a concomitant disease of a subarachnoid hemorrhage
Approximately 150 ml of cerebrospinal fluid (CSF) is produced every day. Due to the localization of the hemorrhage, the cerebrospinal fluid spaces stick together so that normal cerebrospinal fluid circulation cannot take place in the usual way.
The cerebrospinal fluid cannot reach the areas where it is reabsorbed by the vascular system. As a result, the inner cerebrospinal fluid spaces expand and can lead to hydrocephalus ("hydrocephalus").
Such hydrocephalus is found in 50 to 55 percent of patients with aneurysm-related bleeding. It is treated acutely with a drain inserted from the outside. This method is known as external ventricular drainage (EVD). A plastic catheter in the lumbar spine area is also possible, in which case it is referred to as lumbar drainage.
In the case of non-aneurysm-related subarachnoid hemorrhage, the risk of EVD is only 14 percent. After approximately two weeks, it is usually decided whether a permanent drainage in the form of a shunt is required. The shunt usually drains the cerebrospinal fluid from the ventricles of the head into the abdominal cavity, less frequently to the heart.
Vasospasm (vasospasm) as a concomitant disease of a subarachnoid hemorrhage
Vasospasms are responsible for the high mortality rate in the period following treatment of a subarachnoid hemorrhage. As a rule, vasospasms occur four days after the bleeding event and last until day 10 to 12.
The vasospasms are caused by blood breakdown products. Measures are primarily aimed at improving blood flow to the brain. This can be achieved by raising the blood pressure, sometimes excessively.
If all measures fail, the affected vascular segments can be dilated locally by the vascular system either mechanically or with medication. Unfortunately, drug treatment is usually only temporarily effective and may have to be repeated.
Sometimes a microcatheter is also left in place in order to administer medication locally over a longer period of time. There is no reliable study data for any of these measures.
However, these measures are only considered if the patient is at risk of suffering a major stroke. This could lead to a severe neurological deficit or death.
After surgical or endovascular aneurysm treatment following a subarachnoid hemorrhage, a follow-up examination should be performed.
Diagnostic angiography using a catheter is still the method with the best detail resolution. Depending on the findings, this is performed once or several times. It is usually carried out once and after approx. six months.
An MRI and MR angiography examination is performed at the same time. The resulting images are compared with the conventional examination. They can also be used as a comparison for further examinations.
These follow-up examinations are important for two reasons:
- to check the local findings with the question of recurrence (reappearance/growth of the original aneurysm), and
- to monitor the other cerebral vessels, as the risk of developing another aneurysm is around 9 to 10 percent.
In around 20 percent of patients with an aneurysm, a further aneurysm can be detected from the outset. Often several aneurysms occur at the same time, which is why appropriate measures should be taken to confirm the diagnosis.
The probability of a second, third or further aneurysm bleeding is also higher than an aneurysm that has not yet bled.
There are currently recommendations (ISUIA study) that an aneurysm measuring 7 mm or more should be treated. This does not apply to secondary aneurysms, which should all be treated if possible due to the high probability of bleeding.
In 86 percent of our own patients with hemorrhaged aneurysms, these were smaller than 7 mm. Thus, with regard to the treatment indication for non-bleeding aneurysms, not only the size but also the morphology of the aneurysm must be taken into account.
- the morphology of the aneurysm,
- the patient's concomitant diseases and
- the age of the patient
should also be included in the discussion.
If an aneurysm is present, sporting activities that lead to high blood pressure should be avoided. This also applies to short-term increases in intracranial pressure, e.g. when pushing during a bowel movement or lifting very heavy loads. Endurance sports without a relevant increase in blood pressure are normally fine.
Very strong increases in blood pressure can also occur during sexual intercourse, so that patients repeatedly suffer a subarachnoid hemorrhage during sexual intercourse.
Flying in small aircraft should be avoided as a matter of principle, as rapid pressure differences could cause the aneurysm to burst. These high pressure differences are not to be expected in modern wide-bodied aircraft, so the risk of this happening is certainly low. This does occur in smaller aircraft and should therefore be avoided.
A subarachnoid hemorrhage in the presence of an aneurysm still has a high mortality rate of 40 to 50 percent. The probability of re-bleeding is
- approx. 4 percent within the first 24 hours,
- 20 percent within 14 days and
- 50 percent within a year.
As every bleeding event is associated with a high mortality rate, the aneurysm should be treated as soon as possible. The results of treatment are associated with a higher complication rate if the surgeon is tired, for example. For this reason, interventions should only be carried out at night under certain circumstances.
Around a third of patients do not survive the initial bleeding. Approximately 15 percent die as a result of the subarachnoid hemorrhage and the treatment. However, the risk of death during treatment is only around 1 percent and is less significant.
Approximately four days after a subarachnoid hemorrhage, patients develop vasospasms due to the resulting blood breakdown products. These can lead to cerebral circulatory disorders with strokes of varying severity.
Of the survivors, around 50 percent of patients are more or less severely disabled. Approximately 40 percent of these patients return to work.
