Encephalocele is a rare birth defect where a sac-like protrusion, often containing brain tissue and its protective coverings, extends through an opening in the skull. This condition is a congenital anomaly and a form of neural tube defect (NTD) that affects the developing central nervous system. It forms very early in pregnancy and poses significant risks to the newborn.
Defining Encephalocele and How It Forms
Encephalocele formation begins during the first month of pregnancy, specifically between the third and fourth weeks of gestation. During this time, the neural tube, the precursor to the baby’s brain and spinal cord, is forming. This tube must fold and close completely to fully enclose the developing nervous system.
Encephalocele occurs when the upper portion of the neural tube fails to close as expected. This closure failure prevents the overlying skull bones from forming correctly, leaving a defect or gap in the cranium. Through this bony opening, the membranes covering the brain, known as the meninges, and often a portion of the brain itself are pushed outward, creating a noticeable sac. The contents of this protruding sac—cerebrospinal fluid (CSF), meninges, or brain tissue—dictate the severity of the condition.
Recognizing the Different Types
Encephaloceles are classified primarily by their anatomical location, which influences potential neurological outcomes. Classification involves the back, front, or top of the head. Occipital encephaloceles, which form at the back of the skull, are the most frequently observed type in North America and Western Europe.
The next major category is the frontal encephalocele, also called sincipital or frontoethmoidal, which occurs around the forehead, nose, and eye area. A frontal encephalocele may not be obvious at birth, sometimes presenting as a lump near the bridge of the nose or between the eyes. Parietal encephaloceles are less common and are found near the top of the head.
The size of the defect and the amount of brain tissue within the sac determine the severity and long-term outlook. Encephaloceles located at the front of the head are generally associated with a better prognosis than those at the back, which are linked to severe nervous system problems. If the sac contains only CSF and meninges, it is termed a meningocele, which is less severe than a meningoencephalocele that includes brain tissue.
Identifying Causes and Risk Factors
The development of an encephalocele is considered to be multifactorial, arising from a complex interaction between genetic and environmental influences. While the exact mechanisms are not fully understood, a significant factor involves maternal nutritional status during the earliest stages of pregnancy. A deficiency in folic acid, a B vitamin, is a well-established risk factor for neural tube defects generally.
Adequate folate stores are necessary for the proper closure of the neural tube. Although the link between folic acid and encephalocele is not as definitively established as it is for other NTDs, it is considered a contributing factor. Genetic predisposition also plays a role, as the condition sometimes runs in families or is associated with specific genetic syndromes.
Other maternal health conditions and exposures during the first trimester can increase the risk of encephalocele. These include pre-existing diabetes that is not well-managed before and during early pregnancy. Exposure to certain prescription medications, such as some antiseizure drugs, has also been implicated. Maternal fever or overheating, potentially from hot tub or sauna use in early pregnancy, has been identified as an environmental factor that may interfere with neural tube development.
Diagnosis and Treatment Pathways
Encephalocele can often be identified before birth during routine prenatal ultrasound examinations. If the initial ultrasound suggests a defect, additional imaging tests are performed to gain a clearer picture. Prenatal magnetic resonance imaging (MRI) is commonly used to visualize brain structures and determine the exact contents of the protruding sac.
The diagnosis is confirmed immediately after birth by a physical examination of the visible protrusion. Postnatal imaging, particularly MRI, is then performed to precisely define the size of the skull defect and the extent of any associated brain abnormalities. This detailed information is crucial for planning the necessary medical intervention.
The standard treatment for an encephalocele is surgical repair, which is usually performed shortly after birth or within the first few months. The primary goals of the neurosurgical procedure are to carefully place any viable brain tissue back into the skull cavity and to remove any non-functional tissue. Surgeons must then achieve a watertight closure of the membranes covering the brain and repair the bony defect in the skull to prevent infection and protect the brain.
Long-term management is necessary due to potential associated neurological effects, such as seizures or the buildup of fluid in the brain (hydrocephalus). Many children require ongoing care from a multidisciplinary team of specialists. This approach includes physical, occupational, and speech therapy to address developmental delays and maximize the child’s physical and cognitive potential.