An Overview of Pediatric Stroke
Stroke occurs in children of all ages; it can even occur in the fetus. Every year, five out of every two hundred thousand children have a stroke. The causes of stroke in children are far different from the usual causes in adults. Children have not had the time to develop hardening of the arteries (atherosclerosis) or other long-term effects of hypertension, high cholesterol, diabetes, and smoking that are among the most common stroke risks in adults. In order to explain this phenomenon, it is necessary to discuss the two major categories of stroke type. The first of these is called ischemic stroke; the second is called hemorrhagic or bleeding type stroke.
Ischemic stroke occurs due to blockage of an artery, usually by a blood clot that has formed at the site of blockage or that has formed somewhere "upstream" in the arterial tree, has broken off, and been carried "downstream" in the blood flow through progressively smaller branches in the arterial tree, until it enters a vessel too small to fit through, plugging it closed. This type of floating blood clot is known as an embolus, and often forms within the heart or one of the larger arteries leading away from it, then breaks off and travels to the brain or another organ. Ischemic strokes are usually associated with disorders that promote the clotting of blood or cause inflammation of arteries (vasculitis, or arteritis) which in turn promotes clotting of blood within them. Another major cause is birth defect of the heart or its valves, which can promote the formation of a clot in the heart, which then becomes an embolus.
The second type stroke, hemorrhagic, occurs when a blood vessel in the brain breaks open or develops a hole in its wall through which blood begins to leak directly into brain tissue or into the clear fluid which surrounds the brain and fills its central cavities (called ventricles). Hemorrhagic or bleeding strokes are usually associated with disorders that inhibit normal clotting of blood and thus create a tendency for bleeding, or are associated with malformations of the blood vessels such as aneurysms. Some disorders paradoxically create simultaneous tendencies for clot formation and for bleeding, increasing the risk for either type of stroke. Additionally, in large ischemic strokes, deterioration of blood vessels in the affected brain tissue can cause them to become leaky and transform the ischemic stroke into a hemorrhagic one.
Strokes occurring in newborns deserve separate discussion. Hemorrhagic strokes in this age group are most commonly associated with premature birth, especially when there is also very low birth weight. The more premature the birth and the lower the birth weight, the greater the risk of hemorrhage. The tendency to develop these hemorrhages is probably due to inadequately developed blood clotting mechanisms, immature and fragile blood vessels, and sometimes to complicated and difficult deliveries. It is less common for hemorrhagic strokes at this age to be caused by aneurysms or other blood vessel malformations.
Bleeding in or around the brain can increase the pressure inside the skull and eventuate in paralysis, coma, and death from squeezing the brain or respiratory failure. Even after surviving the initial bleed, the baby can later develop an excess or an entrapment of the clear fluid that surrounds the brain and fills its vesicles, resulting in another more chronic high-pressure condition known as hydrocephalus. Since infants have not yet had complete fusion of all the curved bone plates that comprise the skull, hydrocephalus can push the plates apart, causing bulging out of the soft spot and enlargement of the size of the head, analogous to the blowing up of a balloon. As a infant ages, the bones harden and become fused, resulting in a permanent enlargement of head size. Normal brain development may be impaired. One way to prevent or minimize hydrocephalus after stroke is to implant a shunt. This is a tube, one end of which is inserted into a brain ventricle. The tube then passes out of the skull through a drilled hole, travels underneath the skin of the scalp and neck, and ends in the abdominal cavity. A one-way valve allows excess brain fluid to escape through this tube in the ventricle and drain out into the abdominal cavity where it is reabsorbed by the body.
Ischemic strokes in newborns are usually related to brain infections acquired in the uterus or during or after birth. These include encephalitis and meningitis caused by a variety of different microorganisms. Such infections can cause inflammation in the brain's blood vessels and alterations in the clotting mechanisms of blood, both of which promote the formation of clots. The other major cause of ischemic stroke in this group is any of various birth defects of the heart or its valves that promote the formation of an embolus.
Strokes in Toddlers and Older Children
Hemorrhagic strokes in this age group can be related to malformations of the blood vessels that are present as birth defects, often inherited, or may develop for unclear reasons over time. The most common of these are aneurysms, which are various types of bulges in the wall of arteries. The bulge may be slight, or may appear like a small berry still attached to the artery by a short stem. The other common type of blood vessel anomaly is called an arteriovenous malformation (AVM). This usually appears as a tortuous tangle of arteries and veins with numerous direct connections between the two types of blood vessels. The arterial walls in the region of aneurysms and AVMs are weaker than in normal segments, and may deteriorate over time. This can result in small slow leaks of blood or in a catastrophic sudden "bursting" bleed. The blood can leak into the fluid around the brain, into the brain tissue, or into the ventricle fluid. As with hemorrhagic strokes of infancy, hydrocephalus may develop later. Sometimes aneurysms and AVMs make themselves known by producing epileptic seizures or other neurological symptoms, and may be amenable to various procedural treatments. Unfortunately, both are often undetectable until a stroke occurs.
Other causes of hemorrhagic stroke may be severe blood vessel inflammation (vasculitis) from a variety of causes including infections, use of blood-thinning medications for various reasons, and disorders such as hemophilia which disrupt the normal clotting mechanisms of blood. Occasionally, certain brain tumors in this age group may disrupt blood vessels within or adjacent to them.
Ischemic strokes in this age group have a multitude of causes. Birth defects of the heart, its valves, and its attached vessels remain an important cause of emboli. Childhood cancers and severe infections of any kind can produce a blood clotting disorder known as disseminated intravascular coagulation, producing local clots or emboli. Sickle cell anemia promotes clot formation and bleeding. Several types of vasculitis affect this age group, the most common being Takayasu arteritis, Kawasaki disease, systemic lupus erythematosus, and hypersensitivity vasculitis.
Another large group of widely varied and heterogenous disorders producing ischemic stroke in this group are collectively referred to as inborn errors of metabolism. These are too numerous to list or elucidate here, but many produce a tendency to form blood clots. Common disorders in this group include homocystinuria and inherited disorders of fat and lipoprotein metabolism.
Other miscellaneous disorders include polycythemia, an overproduction of blood cells, which can cause "thickening" of blood, increasing its viscosity and its clotting tendency. Rare causes include oddly named disorders such as Moyamoya disease is a slowly progressive occlusion and deterioration of arteries in the rear part of the brain. There is also an enigmatic entity known as MELAS, which stands for mitochondrial encephalopathy, lactic acidosis, and stroke. In this age group, trauma to the neck area can disrupt the walls of carotid or other arteries carrying blood to the brain, producing occlusion, clot, or embolus.
Strokes in Older Children
All of the disorders producing stroke in toddlers and school-aged children may still produce stroke in adolescents. However, an increasing percentage of strokes, of both ischemic and hemorrhagic types, occur in relation to drug use. The most common drug causing stroke is cocaine in its smoked form (crack). Smoked amphetamines (meth, ice, etc.). Any type of illicit drug injected into the bloodstream can produce stroke.
The Effects of Strokes in Children
As with adults, the functional deficits caused by the stroke depend on ins size and the specific areas of the brain affected. Paralysis of affected limbs and subsequent development of spasticity in those limbs can occur if motor areas are affected. Balance mechanisms are impaired if the cerebellum or its related structures are involved. Language deficits (aphasia) occurs if language areas are involved. The list is as long as that for adults. Children, however, have more "plasticity" in their brains. This means that the areas of the brain have not yet been "locked" into their lifelong function. Thus other areas of the brain can "take over" the function of destroyed parts to a somewhat greater degree than in adults. The result is that children with stroke tend to have a greater degree of recovery in the long term than adults do. The younger the child at the time of stroke, the greater this tendency.
© Mayank Pathak, M.D.
SAFE (Stroke Awareness for Everyone, Inc.) has been given permission to reproduce this article by its author, Mayank Pathak, M.D. Dr. Pathak is Staff Physician, at The Parkinson's and Movement Disorders Institute, Fountain Valley, California.
If you are a parent or family member of a child who has had a stroke, SAFE would like to direct you to two excellent support organizations for families of children with stroke: CHASA: Children's Hemiplegia and Stroke Association and Pediatric Stroke Network.