Cerebral Ischemia

Cerebral ischemia is an ischemic condition where the brain or parts of the brain do not receive enough blood flow to maintain normal neurological function. Cerebral ischemia can be the result of various diseases, or the result of arterial obstruction such as strangulation. Similarly to cerebral hypoxia, severe or prolonged cerebral ischemia will result in unconsciousness, brain damage or death, mediated by the ischemic cascade.

Carotid arterial stenosis is a narrowing of the lumen of the carotid artery, usually by atheroma (a fatty lump or plaque causing atherosclerosis). Atheroma's may cause transient ischemic attacks (TIAs) and cerebrovascular accidents (CVAs) as it obstructs the bloodstream to the brain. It also has the potential to generate emboli (blood clots) that obstruct the cerebral arteries.

The narrowing can either be asymptomatic (causing no medical problems) or presents with sympotms such as TIAs and CVAs.

Carotid stenosis is usually diagnosed by ultrasound scan of the neck arteries. This is the first imaging option and usually used for follow up and observation as it involves no radiation and no contrast agents that may cause allergic reactions.

If there is doubt whether the narrowing is still patent (open to blood flow) and the patient is to be assessd for treatment, the next imaging option would either be computed tomography angiogram (CTA) or a magnetic resonance imaging angiogram (MRA).

CTA is usually used as it's more widely available and faster (takes only several minutes). However, it does involve significant X-ray radiation and the use of contrast agents which is usually iodinated, which can cause allergic reactions, even anaphylaxis and can also cause renal failure.

MRA takes much longer to complete, more costly and not yet as widely available.

Carotid endarterectomy (CEA) is a surgical procedure used to correct carotid stenosis (narrowing of the carotid artery lumen by atheroma), used particularly when this causes medical problems, such as transient ischemic attacks (TIAs) or cerebrovascular accidents (CVAs, strokes). Endarterectomy is the removal of material on the inside (end-) of an artery. Angioplasty and stenting of the carotid artery are undergoing investigation as alternatives to carotid endarterectomy.

The internal, common and external carotid arteries are clamped, the lumen of the internal carotid artery is opened, and the atheromatous plaque substance removed. The artery is closed, hemostasis achieved, and the overlying layers closed. Many surgeons lay a temporary shunt to ensure blood supply to the brain during the procedure. The procedure may be performed under general or local anaesthesia. The latter allows for direct monitoring of neurological status by intra-operative verbal contact and testing of grip strength. With general anaesthesia indirect methods of assessing cerebral perfusion must be used, such as electroencephalography (EEG), transcranial doppler analysis and carotid artery stump pressure monitoring. At present there is no good evidence to show any major difference in outcome between local and general anaesthesia.

Non-invasive procedures have been developed, by threading catheters through the femoral artery and up through the aorta, and then inflating a balloon to to dilate the carotid artery, with or without a wire-mesh shunt.

The aim of CEA is to prevent the adverse sequelae of carotid artery stenosis secondary to atherosclerotic disease, i.e. stroke. As with any prophylactic operation, careful evaluation of the relative benefits and risks of the procedure is required on an individual patient basis. Peri-operative combined mortality and major stroke risk is 2 – 5%.

Carotid stenosis is diagnosed with ultrasound doppler studies of the neck arteries or magnetic resonance arteriography (MRA). The circle of Willis typically provides a collateral blood supply. Symptoms have to affect the other side of the body; if they do not, they may not be caused by the stenosis, and arterectomy it will be of minimal benefit.

The procedure cannot be performed in case of:

* Complete internal carotid artery obstruction (because the intraluminal thrombus then extends too far downstream, well into the intracranial portion of the artery, for endarterectomy to be successful).

* Previous stroke on the ipsilateral side with heavy sequelae because there is no point in preventing what has already happened.

* Patient deemed unfit for the operation by the anaesthesiologist.

About 3% of patients will suffer neurological complications as a result of the procedure. Hemorrhage of the wound bed is potentially life-threatening, as swelling of the neck due to hematoma could compress the trachea. Rarely, the hypoglossal nerve can be damaged during surgery. This is likely to result in fasiculations developing on the tongue and paralysis of the affected side: on sticking it out, the patients tongue will deviate toward the affected side.