A cerebral aneurysm (sometimes called a Berry Aneurysm or Saccular Aneurysm) is a weak spot in an artery carrying blood to the brain, causing a bulge in the blood vessel, similar to that seen on an inner tube of a worn bicycle tyre.
Aneurysms tends to occur at the branch in the vessel, usually near the base of the brain, where the blood vessel (artery) lies in the fluid filled space surrounding the brain (called the subarachnoid space).
The vast majority of aneurysms are thought to be due to a congenital, or inborn weakness of the blood vessel wall. Women are slightly more prone to aneurysms than men.
They are very rare in childhood, but increase in incidence with increasing age. Approximately 2-3% of the adult population will develop an aneurysm over a lifetime, but most never cause a problem. Of those with an aneurysm, 15% will have more than one.
Some families have a tendency for aneurysms, increasing the incidence in those families. A small number of diseases (for example, polycystic kidney disease, connective tissue disorders) are associated with an increased incidence of aneurysms, but these are rare.
Other less common causes include head trauma, infection and chronic drug use (particularly cocaine).
Aneurysms can become apparent if they bleed, causing a subarachnoid haemorrhage. This is a medical emergency requiring urgent diagnosis and treatment in a major hospital.
Aneurysms can enlarge and cause increasing headache, or can compress nerves, causing either pain or weakness in the muscles supplied by the nerve (this may for instance cause double vision or even blindness in one eye).
With increasing use of CT and MRI (Magnetic Resonance Imaging) scans, a number of aneurysms are detected incidentally during an investigation for an unrelated matter.
The greatest concern is the risk of rupture causing subarachnoid haemorrhage. Subarachnoid haemorrhage can cause death and permanent disability. The risk of an aneurysm rupturing depends on a number of factors.
Firstly, the size of the aneurysm - generally, the larger the aneurysm, the greater the risk of rupture. The exact figures are difficult to determine, but roughly, the risk of rupture for an aneurysm < 3mm is very small, much less than 1% per year.
The risk is approximately 1% per year for aneurysms between 7-12mm, 3% per year for 12-24mm aneurysms, and over 10% per year if the aneurysm is >24mm. Other factors thought to increase the risks are high blood pressure, smoking, drug use (particularly cocaine), and a previous history of ruptured aneurysms.
The shape of the aneurysm, particularly if the aneurysm wall is “bumpy” is also thought to influence the risk.
If an aneurysm has ruptured, or is enlarging causing nerve compression, urgent treatment is required by Endovascular Neurointerventional techniques (also termed endovascular coiling) or Neurosurgical techniques.
Unruptured aneurysms may or may not require treatment, based largely on the risk of rupture. The question as to whether treatment is necessary is complex, and needs to be discussed with experts involved in treating aneurysms, such as an Endovascular Neruointerventionist.
Risk of rupture, risks of treatment, age of the patient and medical history (general health) will all influence the final decision, which ultimately is made by the patient and treating doctor.
At the Cerebrovascular Foundation, we have a team approach. Each individual case is discussed at a combined meeting which is attended by Endovascular Neurointerventionists and Neurosurgeons. A special clinic is used to discuss options with the patient.
CTA ( Computed Tomographic Angiography) is a commonly used technique for assessment and follow up of aneurysms. It is an xray technique involving injection of a contrast agent into a vein during a CT scan. It is painless, although does cause a short lived minor hot flush. It is not suitable some patients with poor kidney function or allergies to iodine containing contrast agents. It is also not suitable in some patients with either clipped or coiled aneurysms due to artefacts caused by the metal clips or coils.
Magnetic Resonance Angiography ( MRA) is a scanning technique on a MRI machine. Usually it does not require a contrast injection, but occasionally contrast is used. Some patients are not able to have MRA (due to metal foreign bodies or pacemakers). Sometimes artefacts caused by treated aneurysm clips or coils make MRA unsuitable.
Cerebral Angiography is an xray technique whereby a fine tube (catheter) is fed through an artery from the groin to the arteries supplying blood to the brain. Contrast is then injected as rapid sequence xrays are taken. This is the most accurate method of assessing aneurysms, and is nearly always performed if an aneurysm is to be treated.
When performed by experts in cerebral angiography, the risks are small ( <1%) , but can include stroke, contrast allergy and vascular damage. It can be performed as a single day stay procedure.
Subarachnoid haemorrhage is a dramatic life threatening condition which can occur if an aneurysm ruptures.
If an aneurysm ruptures, arterial pressure bleeding into the fluid filled space surrounding the brain (subarachnoid space) occurs producing dramatic symptoms. Patients typically experience the sudden onset of the worst headache of their life (thunderclap headache), often associated with stiffness in the neck, sensitivity to light, nausea, vomiting and sometimes loss of consciousness and fitting.
Risks of subarachnoid haemorrhage vary on a number of factors, but roughly 40% die, 30% will suffer permanent disability, with the remaining 30% recovering well. The severity of the bleed is graded from 1 to 5 depending on the conscious level of the patient. With grade 1 patients, the patient is conscious and relatively alert, whereas with Grade 5 patients, the patient is deeply comatose.
Treatment, whether by endovascular neurointervention (coiling) or by neurosurgery (clipping) is usually indicated if a subarachnoid haemorrhage has occurred.
At the Royal Melbourne Hospital, the majority of patients with subarachnoid haemorrhage due to aneurysm rupture are investigated with a CTA and a cerebral angiogram, and treated (either by clipping or coiling) within the first 24 hours following presentation.
Following treatment of the aneurysm, an period of 7 – 10 days of expert intensive care, either in the high Dependency Unit or Intensive Care Unit. Various drugs and fluid therapies are administered to help prevent narrowing of the cerebral arteries (spasm) which can be caused the blood in the subarachnoid space.
Complications such as hydrocephalus ( blockage of the fluid pathways which may require a drain (shunt) tube to be placed), epilepsy (seizures) or general complications such as chest infection etc can be monitored and treated.
A large number of patients can be discharged home after 10 –14 days, but a number need rehabilitation prior to going home.