 Introduction
A cerebral aneurysm is a cerebrovascular disorder in which weakness in the wall of a cerebral artery leads to a localized dilation or ballooning of a blood vessel. The layer of the artery that is in direct contact with the flow of blood is called the tunica intima. This layer is made up of endothelial cells. Just deep to this layer is the tunica media, known as the media. This "middle layer" is made up of smooth muscle cells and elastic tissue. The outermost layer is known as the tunica adventitia or the adventitia. This layer is composed of connective tissue.
Cerebral aneurysms are described according to their shape: Saccular or fusiform. Saccular aneurysms are round, berry shaped, while fusiform aneurysms are more dilated and broad.
Aneurysms can be also broken down into two additional groups: true aneurysms and false aneurysms. A true aneurysm involves an outpouching of all three layers of a blood vessel: the intima, the media, and the adventitia. True aneurysms can be due to congenital malformations, infections, or hypertension. A false aneurysm, also known as a pseudoaneurysm, involves an outpouching of only the intima only. These are usually caused by trauma or dissection.
A common location of cerebral aneurysms is on the arteries at the base of the brain, known as the Circle of Willis. Cerebral aneurysms occur more commonly in adults than in children and are slightly more common in women than in men, but they may occur at any age.
Symptoms
A small, unchanging aneurysm may produce no symptoms. However, aneurysms can enlarge which makes them high risk for rupture. When an aneurysm ruptures, the patient may experience a sudden and usually severe headache ("worst headache of my life"), nausea, vision impairment, vomiting, and loss of consciousness. Often people will notice a change in vision in one eye with changes in their pupil size. Onset is usually sudden and without warning. Rupture of a cerebral aneurysm is life threatening and usually results in bleeding into the coverings of the brain (subarachnoid hemorrhage) or the brain itself (intracranial hemorrhage).
The symptoms of a ruptured cerebral aneurysm are graded using the Hunt and Hess scale of subarachnoid hemorrhage severity:
Grade 1: Asymptomatic; or minimal headache and slight nuchal (neck) rigidity.
Grade 2: Moderate to severe headache; nuchal rigidity; no neurologic deficit except cranial nerve palsy.
Grade 3: Drowsy; minimal neurologic deficit.
Grade 4: Stuporous; moderate to severe hemiparesis; possibly early decerebrate rigidity and vegetative disturbances.
Grade 5: Deep coma; decerebrate rigidity; moribund.
Diagnosis
The diagnosis of a cerebral aneurysm is made using neuroimaging modalities. A CT scan usually is the first study ordered and often shows a significant hemorrhage within or around the brain. This study is often followed up by a CT-angiogram, which is a specialized CT scan looking specifically at blood vessels. A formal angiogram is often ordered as well to look at the cerebral blood vessels. MRI studies can be useful as well.
Lumbar punctures are often performed initially to look for evidence of bleeding into the fluid that surrounds the brain. This fluid will often look red or yellow (xanthochromic).
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| CT scan showing blood (white) in the subarachnoid space |
Formal angiogram showing aneurysm
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Treatment
Emergency treatment for individuals with a ruptured cerebral aneurysm generally includes admission to an intensive care unit (ICU). Often patients will need to be resuscitated and placed on mechanical ventilation. Hydrocephalus (excess brain fluid) develops in some patients because of blockage of the normal CSF drainage pathways and this needs to be treated emergently with a ventriculostomy (an external drainage tube placed into the ventricles of the brain to drain fluid).
Surgery is usually performed within the first three days to obliterate the ruptured aneurysm to reduce the risk of rebleeding. Modern treatment of aneurysms involves either open neurosurgical procedures involving a craniotomy and clipping of the aneurysm, or endovascular procedures which involves microcoil thrombosis of the aneurysm. Deciding which procedure to perform is dependant on the location, size, and shape of the aneurysm as well as the condition of the patient.
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| Microcoils placed into an aneurysm |
Aneurysm clip |
Patients are at high risk of developing vasospasm within the first two weeks of their initial bleed and need to be monitored closely for any changes in neurological function. Vasospasm results in stroke like symptoms due to vasoconstriction of irritated blood vessels from the blood products. If vasospasm develops patients are treated with medication, fluids and interventional procedures such as angioplasty.
Other treatments involve bedrest, anti-vasospastic drug therapy, and hypertensive-hypervolemic therapy (which elevates blood pressure, increases blood volume, and thins the blood) to drive blood flow through and around blocked arteries and control vasospasm.
Prognosis
The prognosis for a patient with a ruptured cerebral aneurysm depends on the extent and location of the aneurysm, the person's age, general health, and neurological condition. One third of individuals with a ruptured cerebral aneurysm die from the initial bleed. Other individuals with cerebral aneurysm recover with little or no neurological deficit. The majority of patients will have some degree of neurological deficit and will require an extended rehabilitation period including physical therapy, occupational therapy and speech-cognitive therapy.
Often patients will need other neurosurgical procedures to control complications of the hemorrhage, such as placement of a ventriculo-peritoneal shunt or a feeding tube.
Over 100 aneurysms are treated each year at the University of Florida Neurovascular center by Dr. Stephen Lewis.
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