Periventricular/Intraventricular Hemorrhage (PVH/IVH) in the Premature Infant
Neal P. Simon, M.D.
The immaturity of the premature infant’s brain makes it inherently more vulnerable to injury. The more premature an infant, the greater the likelihood of brain damage. While all areas of the premature infant brain can be injured, the area most vulnerable to injury is the "periventricular" area.
The periventricular area is a rim of brain tissue that lines the outside of the lateral ventricles.** Each periventricular area contains a rich network of small blood vessels called capillaries. The more premature the infant, the more capillaries there are in the periventricular areas. Unfortunately, these capillaries are extremely thin and fragile and can easily rupture.
When a fetus is born prematurely, the infant is suddenly thrust from a well-controlled uterine environment into an highly stimulating, hostile one. The tremendous physiologic stress and shock experienced by a premature infant after birth may cause the periventricular capillaries to rupture. Bleeding occurs initially in the immediate periventricular areas causing a "periventricular" hemorrhage or "PVH." If the bleeding persists, the expanding volume of blood dissects into the adjacent lateral ventricles leading to an "intraventricular" hemorrhage or "IVH." Neonatal medical personnel often refer to these hemorrhages as "blood clots" in the brain. The size and severity of hemorrhage is graded from 1 (mild) to 4 (severe). Both periventricular areas generally experience the same grade of hemorrhage although on occasion the hemorrhage may be worse on one side than the other.
Some periventricular/intraventricular hemorrhages occur before birth. These usually result from pregnancy or labor complications. The majority of hemorrhages occur after birth within the first week of life. This is the period of time when premature infants are most critically ill and under the greatest amount of physiologic stress, requiring life saving resuscitation and intensive life support. To make matters worse, the more immature infants who are at greatest risk for PVH/IVH typically require the most intensive and invasive life support. The incidence of PVH/IVH ranges between 15% and 40% in infants less than 32 weeks gestation or birthweights less than 1500 grams (approximately 3 pounds).
** (The lateral ventricles are a pair of C-shaped reservoirs filled with cerebrospinal fluid located near the center of the brain. There is a lateral ventricle, and therefore a periventricular area, located in each half of the brain.)
Neurodevelopmental Outcome from PVH/IVH
The periventricular areas are important for two reasons:
They are the sites for the formation and development of new brain cells that eventually migrate and form the outer layers of the brain (cerebral cortex). The cerebral cortex is responsible for intelligence and learning, speech, behavior and personality, and influences muscle strength and control.
Motor nerve pathways carrying signals from the cerebral cortex to the muscles pass through the periventricular areas.
There are several mechanisms by which PVH/IVH may cause brain injury. The susceptible new brain cells under development in the periventricular areas are damaged. When these damaged cells eventually migrate and become incorporated into the growing cerebral cortex, the structure and function of the cerebral cortex can be adversely affected. Convulsions, mental retardation, various learning disabilities, language difficulties, and behavior and personality disorders may result. Unfortunately, the different areas of the cerebral cortex are not even used by an infant for months or even years after birth, so it may take this length of time before developmental problems resulting from damage to the cerebral cortex become evident. This emphasizes the need for long-term developmental follow-up for high-risk infants.
Hemorrhage in the periventricular areas may also damage the motor nerve pathways connecting the cerebral cortex to the muscles. The electrical signals to the muscles are interrupted. The muscles generally become too tight (spastic or hypertonic) or too loose (hypotonic) and voluntary muscle control is lost. The infant or child may experience involuntary, non-purposeful motor movements ("athetoid", "choreoform", or "choreoathetoid" movements). This loss of normal strength and voluntary control of the muscles is called "cerebral palsy". The type and severity of cerebral palsy depends upon the number and location of the motor nerve pathways that are damaged from the hemorrhage. Since all infants are born with some degree of muscle strength and motor skills, cerebral palsy can usually be detected at an earlier age, typically within the first 1-2 years of life.
Generally, infants with mild PVH/IVH (grades 1 and 2) have a much better developmental outcome than infants with severe PVH/IVH (grades 3 and 4).
A serious medical complication that may arise from PVH/IVH that has significant developmental consequences is "post-hemorrhagic hydrocephalus", i.e. "water on the brain." Cerebrospinal fluid is continuously being produced in the lateral ventricles. There are drainage holes that normally prevent the cerebrospinal fluid from building up in the ventricles. Periventricular blood that has dissected into the lateral ventricles may plug the drainage holes, causing the lateral ventricles to become overdistended with cerebrospinal fluid resulting in hydrocephalus. As the lateral ventricles continue to enlarge, they push against the adjacent brain tissue. The pressure exerted on the surrounding brain tissue may cause further brain damage.
Initial treatment may involve repeated lumber punctures or medications. Ventricular reservoir or shunt placement is reserved for infants who do not respond to more conservative therapy. Some infants experience spontaneous resolution of the posthemorrhagic hydrocephalus. Grades 3 and 4 PVH/IVH are more likely to cause posthemorrhagic hydrocephalus.