4.4. Stroke
Defining a 'Stroke'
A stroke (aka cerebrovascular accident, or CVA), is a reduction in the blood supply to an area of the brain due to a clot ('infarct') or bleed ('haemorrhage').
Biological Processes Underlying a Stroke
When an infarct or haemorrhage occurs in a blood vessel in the brain, there are two identifiable areas of damage: an ischaemic core and an ischaemic penumbra.
The ischaemic core is the site of the infarct or haemorrhage and the immediate surrounding brain tissue - irreparable damage due to neurons dying occurs here quickly because of the lack of oxygen and glucose being delivered to brain tissue.
The ischaemic penumbra is the nearby surrounding brain tissue that is mildly or moderately damaged and can survive for a number of hours after the stroke; this is because the brain tissue is supplied by collateral arteries from other large arteries and so it still receives some blood. Pharmacological interventions, such as the administration of clot-busting drugs, are more likely to be successful in the ischaemic penumbra rather than the ischaemic core.
So, what are the symptoms of a stroke? The symptoms of a stroke are closely related to the area of brain tissue that has lost its blood supply. For example...
Anterior cerebral artery (ACA) infarct - lower limb dominant motor weakness, e.g. unable to flex hip or knee. This is because the medial portion of the primary motor cortex is supplied by the ACA. There may be dyspraxia and emotional features too, as the prefrontal cortex receives blood from the ACA.
Middle cerebral artery (MCA) infarct - can lead to upper limb and facial dominant motor weakness function. This is becasuse MCA is responsible for providing much of the blood supply to the lateral aspect of the precentral gyrus, in which the primary motor cortex is located. Infarcts or haemorrhages that occur in the lateral striate arteries (early branches of the MCA) can cause particularly widespread brain damage. This is because these arteries supply blood to a structure called the internal capsule, which is responsible for conveying fibres between the cerebrum and the diencephalon and brainstem. Therefore, a infarct or haemorrhage in these arteries can prevent large parts of the cerebral hemispheres from communicating with the rest of the brain and body. Broca's is supplied by the MCA too, so interruption to the MCA can lead to Broca's aphasia, aka expressive aphasia.
Posterior cerebral artery (PCA) infarct - can lead to vision loss (specifically, 'contralateral hemianopia with macular sparing) and memory problems, as the PCA supplies blood to the occipital cortex (where the primary visual cortex is located) and the hippocampus.
It’s also important to realise that a haemorrhagic stroke can be just as devastating as an infarction. Sometimes a haemorrhagic stroke occurs when a blood vessel ruptures because of a weak arterial wall (aneurysm), and the blood pours into nearby tissues and gathers in a pool. If this pool of blood becomes very large, it can increase the intracranial pressure (the pressure inside the skull) and other areas of brain tissue can become compressed. This is life-threatening.
Diagnosing and Managing a Stroke
One of the first aid recommendations for establishing if a stroke is occurring is to perform a FAST test. FAST stands for Face, Arm, Speech, Time to call an ambulance.
Face, you ask the patient to smile - an uneven smile may indicate a stroke.
Arms, you ask the patient to raise and hold both arms - if unable to raise and/or hold, it may indicate a stroke.
Speech, you ask the patient to repeat a simple phrase - slurred speech or unable to speak may indicate a stroke.
This is now being expanded, especially in America, to encompass B=balance and E=eyes, so mnemonic becomes BEFAST. This helps to catch posterior circulation strokes.
In hospital, a CT head scan can establish the presence of an infarct or haemorrhage. It is sometimes necessary for the medical team to put a tube into the patient’s trachea and breathe for them (endotracheal intubation), as the stroke may have disrupted the tone of the tongue, pharynx and larynx. This also means that the patient is helped to lie still for the CT scan so a high quality image can be obtained.
In hospital, if a stroke is identified on a CT scan, there are a number of treatment options. A thrombolytic drug called alteplase (or tenecteplase) can be administered as an IV injection followed by an IV infusion. This is sometimes called a clot-busting drug. Alteplase dissolves the infarct (also called a thrombus) and thus allows restoration of blood flow. Alteplase treatment is most effective if started within four and a half hours of the onset of a stroke. Alteplase is not administered to a patient with a haemorrhagic stroke as it could lead to even more extensive bleeding in the brain.
The treatment for a haemorrhagic stroke is different. If there is bleeding into the subdural space, surgery may be performed to relieve the pressure inside the cranium. A section of the cranium is removed in a procedure called a craniotomy and the excess blood is drained away, or Burr holes can be made to drain blood. Antihypertensive medications, including beta blocker and GTN infusions, are also used in haemorrhagic strokes to lower blood pressure.
For patients who have had any type of stroke, anti-hypertensive and anticoagulant medications may be offered as long-term treatment to prevent more strokes in the future.
