A stroke, or cerebrovascular accident as it is otherwise called, occurs when there is an interruption of blood supply to the brain as a result of a clot or rupture of a blood vessel. A clotted blood vessel causes an ischemic stroke (no blood), whereas a ruptured blood vessel causes a haemorrhagic stroke (blood).

We are all aware of loss of function on one side of the body and slurred speech resulting from a stroke. A simplified way of looking at this is that the brain is divided into two halves (cerebral hemispheres), and one side of the brain controls the opposite side of the body, so that a stroke on the right side of the brain will cause loss of power on the left side of the body, so called hemiplegia or hemiparesis, depending on how much power is lost.

The truth though is that the situation is much more complex and it is possible to have loss of function on the same, opposite or both sides of the body, depending on the area of the brain affected.

RISK FACTORS

Risk factors for stroke include those that can be changed, treated or controlled, and those that cannot.

Controllable/treatable risk factors include:

Controllable/treatable risk factors include:

• High blood pressure: The leading cause of stroke;

• Cigarette smoking: The use of oral contraceptive pills increases the risk;

• Diabetes Mellitus;

• Disease of the carotid arteries (neck arteries) and other arteries in the body, including leg and arm arteries.

• Atrial fibrillation and other heart disease;

• Sickle cell anaemia;

• High blood cholesterol; and

• Physical inactivity and obesity

Risk factors that can’t be changed:

Risk factors that can’t be changed:

• Age: The chance of having a stroke doubles for every decade after age 55;

• Heredity: Risk may be greater if a close family member had a stroke;

• Race: Risk is higher in black race;

• Sex: Women have more stroke than men; and

• Prior stroke, TIA (warning strokes) or heart attack.

Imagine sitting at the table having dinner with the family and grandma suddenly starts slurring her speech, complaining of being unable to move one side of her body or worse, loses consciousness. Did you know that there is a three-hour window in which brain tissue can be saved and the effects of a stroke can be reversed?

Acute stroke management in countries with developed stroke centres focuses on rapid transportation of stroke victims to the centre; rapid evaluation of the area of involved brain and differentiation dead and injured brain; and administration of medication within the patients veins or arteries to break down the clot causing the stroke, in an attempt to restore blood flow to the injured brain.

Acute stroke management is a multispecialty team effort, including emergency medical technicians, emergency medicine doctors, nurses, radiologists, and neurologists to name a few of the people involved. For the purposes of this article, we will focus on the role of the radiologist in emergency stroke management.

Imaging in patients with acute stroke should be geared towards assessment of the four Ps:

1. Parenchyma: Assess early signs of acute stroke and rule out bleeding in the brain.

2. Pipes: Assess the blood vessels of the neck and brain for evidence of narrowing or blockage.

3. Perfusion: Assess cerebral blood flow, cerebral blood volume and mean transit time.

4. Penumbra: Assess the brain tissue at risk of dying if blood flow to the affected part of the brain is not restored.

CT AND MRI EVALUATION

Computed tomography (CT) and magnetic resonance imaging (MRI) evaluation of the brain are the mainstay of acute stroke imaging.

Role of CT

Role of CT

There are three key CT techniques used in the work-up of acute stroke: Unenhanced imaging (no IV contrast given), angiography (study of the blood vessels with IV contrast), and perfusion imaging.

Unenhanced CT not only identifies haemorrhage (a contraindication to thrombolytic therapy), but it can help detect early-stage acute stroke.

Signs on CT of acute stroke include the hyperdense artery sign, insula ribbon sign and obscuration of the lentiform nucleus. These signs are all named according to the areas of the brain affected by these early signs.

CT angiography in stroke imaging identifies clot within the blood vessels of the brain and the carotid and vertebral arteries of the neck. Administering medication within the arteries rather than veins to dissolve the arterial blockage may be more beneficial in patients with a large blockage. Therefore, CT angiography can guide the type of medication and route of delivery. Demonstration of carotid arterial disease and visualisation of the arch of the aorta may provide further clues to the cause of the stroke and guidance for the interventional radiologist who may choose to physically remove the clot.

CT perfusion imaging can show cerebral (brain) blood volume, cerebral blood flow and the time difference between arterial inflow of blood and venous outflow. This difference is called the transit time. The point of perfusion imaging is to differentiate between brain with decreased blood volume (infarcted or dead brain) and brain with normal blood volume but decreased blood flow increased transit time (ischemic or threatened brain).

Role of MRI

Role of MRI

A combination of conventional MR imaging, MR angiography and diffusion, and perfusion-weighted MR imaging techniques can be used to investigate stroke. MRI is actually more sensitive and specific for the detection of acute stroke, but MRI is more expensive than CT and not as readily available.

MR angiography is useful for detecting intravascular occlusion due to a thrombus, and also for evaluating the extracranial circulation similar to a CT.

Diffusion and Perfusion MR sequences: The physics behind obtaining these sequences is complex, but the take-home message is that MRI is able to age a stroke — that is, tell roughly how long ago the patient had the stroke and also to differentiate between infracted or dead brain tissue and ischemic or injured brain tissue.

The goal of stroke imaging should be to help save brain tissue and minimise the effects of a stroke. The technology and thrombolytic medications are available in Jamaica, but both cost and accessibility are prohibitive. Through a national consensus as well as public/private sector partnerships, it is hoped that one day soon radiologists will help to play a role in minimising the effects of this debilitating event.

Dr Duane Chambers is a consultant radiologist and founding partner of Imaging and Intervention Associates located at shops 58 and 59 Kingston Mall, 8 Ocean Boulevard. He may be contacted through the office numbers 618-4346 or 967-7748.

Dr Duane Chambers is a consultant radiologist and founding partner of Imaging and Intervention Associates located at shops 58 and 59 Kingston Mall, 8 Ocean Boulevard. He may be contacted through the office numbers 618-4346 or 967-7748.