Hydrocephalus is a condition characterized by an abnormal accumulation of cerebrospinal fluid (CSF) within the brain’s ventricles. This excess fluid leads to a widening of these cavities, placing pressure on the brain’s tissues. Ultrasound is a primary, non-invasive tool for detecting this condition during prenatal screenings by allowing for the identification of enlarged ventricles.
Identifying Hydrocephalus on an Ultrasound
An ultrasound identifies hydrocephalus by detecting enlarged ventricles, a condition known as ventriculomegaly. Sonographers measure the atrial diameter of the lateral ventricles, and a measurement greater than 10 millimeters is considered abnormal. The severity is categorized based on these measurements; a measurement between 10 and 15 millimeters is classified as mild to moderate, while an atrial diameter exceeding 15 millimeters indicates severe hydrocephalus.
Another visual cue is a “dangling choroid sign,” where the choroid plexus appears to float in the excess fluid. A separation of more than 3 millimeters between the choroid plexus and the ventricle wall can also indicate an issue. Detection can occur late in the first trimester, but the dilation of the ventricles becomes more clearly visible around 20 to 24 weeks of gestation.
Potential Causes and Associated Conditions
The presence of enlarged ventricles on an ultrasound prompts an investigation into the underlying cause. One major category is obstructive, or non-communicating, hydrocephalus, which occurs when a physical blockage prevents the normal flow of CSF. A common example is aqueductal stenosis, a narrowing of the channel that connects two of the brain’s ventricles.
Developmental issues within the fetus can also lead to hydrocephalus. Conditions such as neural tube defects, like spina bifida, are frequently associated with it. Other brain malformations, including Dandy-Walker malformation and Chiari malformations, are also contributing factors.
External factors, such as maternal infections like cytomegalovirus (CMV) and toxoplasmosis, are known to be associated with fetal hydrocephalus. Genetic components or chromosomal abnormalities can also be identified as the root of the condition.
Diagnostic Steps After an Ultrasound Finding
Following an initial ultrasound that suggests hydrocephalus, the next step is a referral to a specialist, such as a Maternal-Fetal Medicine (MFM) doctor. They will often recommend a more advanced, high-resolution ultrasound to get a clearer picture of the fetal brain and to look for any associated abnormalities.
A fetal MRI may be recommended to provide more detailed images of the brain tissue and the ventricular system. This can help identify the specific cause of the hydrocephalus, such as a blockage or other structural issues.
In addition to imaging, genetic counseling and testing may be offered. An amniocentesis can be performed to test for chromosomal abnormalities or genetic syndromes that may be the underlying cause. Ongoing monitoring with serial ultrasounds is standard to track the size of the ventricles and the progression of the condition.
Understanding Prognosis and Postnatal Management
The prognosis for a baby diagnosed with hydrocephalus is highly variable. The outcome depends on the underlying cause, the severity of the ventriculomegaly, and the presence of other associated abnormalities.
In cases of isolated and mild ventriculomegaly, the condition may resolve on its own before birth or result in normal neurological development. More severe cases, however, often require intervention after birth. Postnatal management begins with close monitoring of the infant’s head circumference, as a rapid increase in head size can indicate that pressure in the brain is increasing.
For infants who require treatment, the goal is to reduce the pressure inside the brain by draining the excess cerebrospinal fluid through a neurosurgical procedure. One common treatment is the placement of a shunt, a thin tube that drains the excess fluid from the brain to another part of the body, like the abdomen, where it can be absorbed. Another surgical option is an endoscopic third ventriculostomy (ETV), where a small hole is created in the floor of a ventricle to allow the trapped CSF to flow.