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Cranial Anatomy - Subarachnoid Haemorrhage

Haemorrhage is the medical term for bleeding. The rupture of one of the brain's blood vessels can cause bleeding into the subarachnoid space - beneath the arachnoid membrane, on top of the pia mater - and into brain tissue. The bleeding usually stops, at least temporarily, when a clot forms over the ruptured area.

Why does it happen?
The most frequent cause of spontaneous subarachnoid haemorrhage (not due to injury) is the rupture of a small aneurysm, or bulging sac, on one of the blood vessels that supplies the brain. It is usually impossible to determine why the aneurysm forms and bursts, but the condition is common in adults and may be associated with aging, diabetes, pregnancy, hypertension (high blood pressure), heredity, or trauma.

Cerebral aneurysms are usually of three types: saccular with a narrow "neck" (called "berry" aneurysms because of their shape and their tendency to occur in clusters); saccular with a broad base; and fusiform, in which a short section of the artery bulges all the way around. Each shape determines the degree of difficulty a surgeon faces in attempting to treat the problem.

An aneurysm ruptures spontaneously - even during sleep - and therefore is not related to the strain of hard work, sexual intercourse, or other physical activity.

Although it is not always possible to discover the exact source of bleeding, other causes of spontaneous subarachnoid haemorrhage include: arteriovenous malformations, small angiomas, certain types of infections, and bleeding disorders.

What symptoms can it cause?

A ruptured cerebral aneurysm at first causes severe headache, which can be followed by nausea, vomiting, double vision or sensitivity to light, neck pain or stiffness, weakness, memory loss, paralysis, coma, or death. How severe the symptoms are and how long they last will depend on the amount and location of the bleeding. Blood in and around the brain can cause pressure, swelling, and brain irritation, which can lead to drowsiness, confusion, weakness or paralysis, memory loss, speech problems, behavior changes, or coma (complete loss of consciousness).

What complications can occur?

The blood vessels around the aneurysm are irritated by the blood from the haemorrhage and will at times go into a state of spasm, tightening and narrowing. This vasospasm ("vaso" meaning vessel) can occur any time after the rupture until the haemorrhaged blood has been absorbed by the body, and it can increase any or all symptoms. It is the body's own attempt to prevent a second haemorrhage by restricting the flow of blood through the vessels around the aneurysm. Vasospasm thus reduces pressure on the delicate aneurysm but unfortunately also reduces the normal blood supply to parts of the brain.
Ongoing research is being done to discover a medicine that will control vasospasm; as yet, none has proven effective. Other complications from subarachnoid haemorrhage, such as hydrocephalus, haematoma (blood clot), and brain swelling, involve the brain; but other body systems can also be affected because of the severe nature of the illness. Pulmonary embolus, heart abnormalities, and bleeding from an ulcer may cause further complications.

How is it diagnosed?

  • Several tests are used to confirm the diagnosis of ruptured cerebral aneurysm. Some are explained in the other parts of this web site.
  • Because cerebrospinal fluid flows within the subarachnoid space, a sample of CSF taken during a spinal tap at the base of the spine will show blood from the haemorrhage.
  • A CT scan will show blood inside the skull and indicate how much bleeding has occurred.
  • To find the source of the haemorrhage, an angiogram is performed, which may have to be repeated to try to pinpoint the aneurysm's exact location.


Because the aneurysm can rupture again, a quiet, restful atmosphere is important. The patient usually is placed in the Intensive Care Unit (ICU), a highly specialised area providing close observation with specialised nursing care. Complete bed rest without physical strain is essential while the patient's condition stabilises - usually in preparation for surgery.

Medications will be given when necessary to reduce pain, control blood pressure, relieve stress, and maintain fluid balance.

If necessary, a respirator may be used to help the patient breathe and to control intracranial pressure (ICP). Most often, however, oxygen is merely administered to the patient through nasal prongs or a mask.

Monitoring devices
Various monitoring devices may be used to assess the patient's condition during recuperation. Among the most common are: an ECG (heart) monitor, an ICP (Intracranial Pressure) monitoring device, a Swan-Ganz catheter to assess the patient's fluid balance, and an arterial line to continuously measure blood pressure and aid in drawing frequent blood samples for laboratory study.

Intravenous (I.V.) fluids may be given until liquids and food can be taken adequately by mouth. The amount of fluid given will be closely monitored until the dangers of brain swelling (edema) and vasospasm lessen.

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