Subarachnoid hemorrhage usually originates from a saccular aneurysm in the Circle of Willis, but it can also occur as a result of trauma, uncontrolled high blood pressure, vasculitis, use of anticoagulants, or stimulants.
The most classic symptom is a sudden-onset headache (thunderclap headache) along with neck stiffness, vomiting, decreased level of consciousness, and seizures. As with any type of stroke, focal neurological deficits are common, and without timely diagnosis or treatment, rapid neurological deterioration may occur.
What is a subarachnoid hemorrhage?
It is a sudden bleeding in the subarachnoid space, which is the area of the brain that contains cerebrospinal fluid, located between the pia mater and the arachnoid, where cerebrospinal fluid (CSF) normally circulates, or when an intracranial hemorrhage extends into that space.
Subarachnoid hemorrhage is a medical emergency, and early diagnosis and hospital admission are essential for proper treatment. When caused by an aneurysm, it carries a high mortality rate, with around 30% of patients dying, one third of them before reaching the hospital. About half of those who survive may be left with some form of lasting disability.
What is the subarachnoid space?
The subarachnoid space is the area between the arachnoid and the pia mater. It is thin due to the adhesion of these two layers. It is partitioned by arachnoid trabeculae and contains cerebrospinal fluid, vascular structures, and nerves.
In certain areas, the arachnoid is separated from the pia mater by wide, partitioned spaces that are freely interconnected, known as subarachnoid cisterns.
Subarachnoid space
Surrounding the brain and spinal cord are three membranous layers known as the meninges. From the surface inward, these layers are the dura mater, the arachnoid, and the pia mater.
The meninges serve to protect the brain and spinal cord from mechanical trauma, support the cranial vasculature, and form a continuous cavity through which cerebrospinal fluid (CSF) circulates.
These membranes collectively define three clinically important spaces: the epidural space, the subdural space, and the subarachnoid space.
Function
The main function of the subarachnoid space is to contain the CSF, which cushions the brain and spinal cord while providing nutrients and removing waste.
The structural components of the subarachnoid space, such as the arachnoid trabeculae, also function to support and stabilize the brain and spinal cord. It also provides a pathway for important neurovascular structures to supply the brain and spinal cord.
Signs and symptoms of subarachnoid hemorrhage
Typically, before rupturing, an aneurysm does not cause symptoms. However, if it does, it may produce the following warning signs:
- Double vision.
- Sudden, severe headache.
Once the aneurysm ruptures, the symptoms are:
- Sudden, intense headache.
- Pain in the face and eyes.
- Double vision.
- Vomiting.
- Dizziness.
- Lower back pain.
- Blurred vision.
- Stiff neck.
- Fainting.
- Alteration of heart rate.
- Breathing problems.
- Seizure episodes.
When a subarachnoid hemorrhage occurs, complications may arise such as:
- Hydrocephalus due to the accumulation of blood and cerebrospinal fluid, which significantly increases intracranial pressure.
- Constriction of the cerebral blood vessels, or vasospasm, which reduces blood flow.
- Rebleeding of aneurysms.
Diagnosis and Treatment of Subarachnoid Hemorrhage
People who are likely to have suffered a subarachnoid hemorrhage are hospitalized immediately. When possible, they are transferred to a center specialized in stroke treatment. Bed rest and avoidance of physical exertion are essential.
Anticoagulant drugs (such as heparin and warfarin) and antiplatelet agents (such as aspirin [acetylsalicylic acid]) are not administered because they worsen the hemorrhage.
Analgesics such as opioids are prescribed (but not acetylsalicylic acid or other nonsteroidal anti-inflammatory drugs, which worsen the hemorrhage) to control severe headaches. Stool softeners are also administered to avoid straining during bowel movements. Such straining puts pressure on the blood vessels inside the skull and increases the risk of rupture of a weakened artery.
To prevent vasospasm and the subsequent ischemic stroke, nimodipine, a calcium channel blocker, is administered, generally orally. Doctors take measures (such as administering medications and adjusting the amount of fluid given intravenously) to keep blood pressure low enough to prevent further bleeding and high enough to maintain blood flow to the damaged parts of the brain.
High blood pressure is treated only if it is severely elevated.
In some cases, a small plastic tube (shunt) is placed in the brain to drain cerebrospinal fluid. This procedure relieves pressure and prevents hydrocephalus.
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