Cerebral aneurysms

What is an aneurysm?
Aneurysm is a dilatation or bulging of a part of the wall of a blood vessel due to some defect. It may remain as such without causing any problem. When it enlarges and becomes big, there is tendency to rupture and cause devastating effects to the patient. Cerebral aneurysm is the aneurysm occurring in the blood vessels of the brain. When the cerebral aneurysm ruptures, it results in bleeding inside the brain and the patient lapses into coma. The exact incidence of aneurysms is difficult to estimate. Recent studies indicate the prevalence of aneurysms as 5%. Ratio of ruptured to unruptured aneurysm is 5:3 to 5:6. Only 2% of the cerebral aneurysms occur in childhood. Aneurysms are more common in females than males and are less common in children.

What are the causes for cerebral aneurysm?
The exact mechanism for the development of aneurysm is still controversial. In contrast to the blood vessels present in the other parts of our body, the blood vessels in our brain contains less elastic in the tunica media and adventitia and the media has less muscle(these are the layers of tissue present in the wall of blood vessels). Also the blood vessels lie in the subarachnoid space with little surrounding supporting tissue, which may predispose to the development of aneurysm. Cerebral aneurysms tend to arise in the branching point of the blood vessels.

The predisposing cause for cerebral aneurysms may be the following:

• Congenital predisposition (defect in the muscular layer of the wall of the blood vessel)
• Atherosclerotic or hypertensive
• Embolic as in atrial myxoma
• Infective- due to bacteria (mycotic aneurysm).
• Traumatic.
• Associated with other conditions like:
• Autosomal dominant polycystic kidney disease
• Fibromuscular dysplasia
• Arteriovenous malformation(congenital malformation of the blood vessels of the brain)
• Marfan's syndrome
• Coarctation of aorta
• Atherosclerosis
• Bacteria endocarditis

In which blood vessels are the aneurysm located?
Aneursyms usually arise in the arteries (which carry pure blood) because of the high-pressure and stress to which these vessels are subjected. Saccular aneurysms or berry aneurysms (the names are due to the shape of the aneurysm) are usually located on major cerebral blood vessels at the apex of the branching point where there is more stress on the blood vessel due to flowing blood. Fusiform aneurysms are more common in the vertebrobasilar system.

Saccular aneurysms are located in carotid system 85-95% of the patients. Anterior communicating artery aneurysm is the most common. Others are posterior communicating and middle cerebral artery aneurysms.5-15 % of the patient has vertebro basilar aneurysm. In 20-30% of the patients, the aneurysms are multiple (that is patients having more than one aneurysm).

What are the symptoms of cerebral aneurysms?
When the aneurysm is not ruptured, it produces no symptoms. Many aneurysms are discovered incidentally, when doing MRI scan for some other reasons. Rupture of the aneurysm causes various type of hemorrhage in the brain. They are

• Subarachnoid hemorrhage (bleeding in between the outer covering layer of the brain)
• Intracerebral hemorrhage (in to the brain substance itself)
• Intraventricular hemorrhage occurs in 13-28 percent of the ruptured aneurysm cases. The prognosis appears to be worse for the patient in this category.
• Subdural hemorrhage.

The patient may have the following symptoms:

• Weakness of limbs or cranial nerve palsies due to pressure effect by large aneurysms compressing the adjacent nervous tissue.
• Visual loss.
• Facial pain syndromes that may mimic trigeminal neuralgia.
• Minor hemorrhage produces headache and neck pain.
• Transient blindness in one eye.
• Seizures.
• Sudden severe headache, which is the worst headache in their life time due to sudden enlargement of the aneurysm or rupture of the aneurysm.
• Some patients may lapse into coma due to severe bleeding and increased intracranial pressure.

How do you diagnose cerebral aneurysm?
The best treatment option depends on the condition of the patient, the location of the aneurysms and the ability of the neurosurgeon. When patient comes with an unruptured aneurysm, surgical clipping of the aneurysms is the best treatment available. Endovascular treatment with guglielmi detachable coils is one of the treatment available where the coils are placed into the aneurysm sac and blocking it. Detachable balloons are also used in endovascular treatment. When the patient comes with ruptured aneurysm in a comatose stage, the prognosis is bad.
Diagnosis is mainly done be a procedure called 4 vessel cerebral angiography. Here contrast agent (dye) is injected in to the patient's blood vessel (artery) and images are taken. Now a days MR angiography, CT angiograghy, Digital substraction angiography are available for the diagnosis of cerebral aneurysm.

What are the treatment options available for treating cerebral aneurysm?

Did you know?
The exact mechanism for the development of aneurysm is still controversial. In contrast to the blood vessels present in the other parts of our body, the blood vessels in our brain contains less elastic in the tunica media and adventitia and the media has less muscle(these are the layers of tissue present in the wall of blood vessels).