Cerebral palsy

With cerebral palsy, “cerebral” refers to the brain, while “palsy” refers to muscle weakness or problems related to movement and posture. So, cerebral palsy refers to a group of movement conditions caused by brain injury that occurs before, during, or shortly after birth.

Before we proceed, let’s focus on three main brain regions that work together to coordinate movement. First is the primary motor cortex, which contains upper motor neurons. These neurons send signals down the spinal cord to lower motor neurons, which then tell muscles to contract. So, upper motor neurons control voluntary movements like grabbing a toy, but they also help regulate muscle tone and reflexes.

The second key structure lies deep inside the brain and is called the basal ganglia. The basal ganglia suppress unwanted muscle activity and help fine-tune our movements. They also play a role in performing learned skills, like riding a bike.

Finally, the cerebellum, which literally means “little brain”, coordinates movements, maintains posture, and controls balance.

Now, injury to any of these structures can lead to cerebral palsy. Depending on the time when the injury occurs, the causes are generally classified into prenatal, perinatal, and postnatal conditions.

Let’s start with prenatal conditions, which can affect the baby while still in the womb. Infections, such as cytomegalovirus, rubella, toxoplasmosis, and Zika virus, can cross the placenta and directly harm the fetal brain. Another major factor is preeclampsia, which occurs when the mother develops high blood pressure during pregnancy. In preeclampsia, here is damage to the small blood vessels in the placenta, reducing the amount of oxygen and nutrients to the growing fetus. Over time, this limited blood flow can interfere with normal brain development. Other prenatal risk factors include poorly controlled diabetes, thyroid conditions, and mercury exposure during pregnancy.

Next up are perinatal conditions, which include complications during labor, delivery, or shortly after birth. One of the most important concerns is early prematurity or being born before the 32nd week of gestation. Very premature infants have fragile blood vessels in the area known as the germinal matrix. These vessels are prone to rupture, which can result in intraventricular hemorrhage, or bleeding into the brain’s ventricles. In severe cases, bleeding can disrupt the normal flow and absorption of cerebrospinal fluid, potentially causing hydrocephalus.

Another important perinatal condition is perinatal asphyxia, or lack of oxygen around the time of birth. The fetal brain is extremely sensitive to poor perfusion and low oxygen levels, but some areas are more vulnerable than others. One of these vulnerable regions includes the watershed zones, which sit at the borders between the anterior, middle, and posterior cerebral arteries.

These zones are supplied by terminal branches of these arteries, meaning they naturally operate under low perfusion. Think of watershed zones like the outer edges of a lawn being watered by multiple sprinklers. The central parts receive plenty of water, but the edges, where the sprays barely reach each other, receive just enough to support lawn growth.

So, during perinatal asphyxia, when blood flow drops, these watershed zones are the first to suffer.

Another high-risk area includes the periventricular white matter, which refers to the white matter around the brain’s ventricle. This region is especially at risk in very premature infants because its blood supply is still developing. When oxygen levels drop, this white matter can break down, which is also known as periventricular leukomalacia. Over time, damaged areas might develop chalky yellow plaques and dystrophic calcifications. In more severe cases, the injury can extend beyond the white matter and affect the cortical and subcortical gray matter, forming cystic lesions across the cerebral hemispheres. This severe form of injury is known as multicystic encephalopathy.

Next up is kernicterus, which is a serious neonatal brain injury caused by extremely high levels of unconjugated bilirubin. This type of bilirubin is lipid-soluble, meaning it can cross the blood-brain barrier and accumulate in areas like the basal ganglia, causing neurotoxicity.