What are Encephaloceles?
Encephaloceles are neural tube defects (NTDs) characterized by sac-like protrusions from a bony defect in the skull cavity. These protrusions are filled with the membranes that surround the brain cavity and, sometimes, brain matter as well. These bony defects are caused by failure of the embryonic neural tube to close properly somewhere between days 24-28 of gestation. The result is a bony defect that allows for development of brain matter, cerebrospinal fluid, and meninges outside of the skull.
The size of the bony defect can vary from a few millimeters to much larger - and the sac can be small or larger than the skull of the fetus. The mass within the sac can be cystic, or it can contain bits of brain tissue.
Encephaloceles most commonly occur at the base of the skull and can also occur between the forehead and nose or at the midline of the upper part of the skull. Encephaloceles are often accompanied by other craniofacial abnormalities and brain malformations.
The prognosis, symptoms, and severity all depend upon the type of brain tissue involved, the location of the encephalocele, and the accompanying brain malformations.
What Causes Encephaloceles?
Like so many other birth defects, the precise cause for encephaloceles is unknown. It's likely that encephaloceles are caused by a combination of a genetic predisposition, maternal nutrition, and exposure to toxins in early fetal life.
Research has shown that encephaloceles may be caused by damage from teratogens, trypan blue, and arsenic. It appears that neural tube defects are associated with a lack of maternal folic acid, which is why women of childbearing ages are recommended to take 400 micrograms of folic acid every day.
What Are The Types of Encephaloceles?
Encephaloceles are often classified into the following categories, based on where they occur and what they involve:
Nasofrontal Encephalocele - present in the nose and forehead.
Nasoethmoidal Encephalocele - present in the nose and ethmoid sinus.
Naso-Orbital Encephalocele - present in the nose and eye.
Meningeocele - bulging sac contains only cerebrospinal fluid and overlying membraine (meniniges)
Encephalomeningocele - brain tissue is also involved in the herniated sac.
Symptoms of Encephaloceles May Include:
Encephaloceles are often accompanied by craniofacial abnormalities and/or other brain malformations.
- Microcephaly- an abnormally small head
- Ataxia - uncoordinated movements of the muscles
- Hydrocephalus - abnormally high levels of cerebrospinal fluid in the brain
- Spastic quadriplegia - paralysis of the arms and legs
- Vision problems
- Mental and growth retardation
Common Conditions Associated With Encephalocele:
Up to 40% of encephaloceles are associated chromosomal abnormalities.
Conditions associated with encephaloceles are:
Dandy-Walker Malformation - enlargement of the fourth ventricle with a cyst that extends to the brain's posterior fossa.
Chiari Malformation - cerebellum of the brain extends into the spinal canal, blocking flow of cerebral spinal fluid, which leads to neurological symptoms.
Meckel Syndrome - term used when an occipital encephalocele is associated with microcephaly, cleft lip and palate, polycyctic kidneys, polydactyly, and ambiguous genitals.
Diagnosis of Encephalocele:
Most encephaloceles are diagnosed on routine ultrasounds. The alpha-fetoprotein (AFP) levels measured in a Quad Screen aren't elevated as the defect is covered by skin. The prenatal ultrasonographic diagnosis of an encephalocele is based on the demonstration of a cranial defect with varying degrees of brain herniation. During the first trimester, ultrasonographic appearance of an encephalocele varies.
The classic ultrasonographic appearance is that of a mass in the midline of the skull, with most cases occurring in the occipital and (less commonly) frontal regions.
If an encephalocele is not diagnosed until birth, the deformity is generally noticeable at birth. In rare instances, an encephalocele - generally a smaller encephalocele in the nasal or forehead region - will remain undiagnosed and undetected for many years.
How Does An Encephalocele Affect A Pregnancy?
After an encephalocele is suspected via prenatal ultrasound, a more thorough ultrasound will be performed by a perinatologist. Accurate diagnosis of the defect is vital to provide an appropriate diagnosis and appropriate genetic counseling. Occasionally, an MRI may be used to get a more accurate picture of the defect and associated anomalies.
As encephaloceles are often associated with chromosomal abnormalities, an amniocentesis may be performed to diagnose any chromosomal anomalies. If the encephalocele is noted to be a part of a syndrome, this may not be necessary. A genetic consultation, however, is suggested for any family whose baby has an encephalocele.
After a more accurate diagnosis of the encephalocele and any associated problems has been achieved, the probable outcome will be discussed with the family. If the prognosis is poor and the pregnancy will be continued rather than terminated, the baby will be offered palliative care after birth.
If the encephalocele is large, the baby's head may not properly fit through the birth canal, so a cesearian birth (c-section) may be performed.
Treatment for Encephaloceles:
Surgery is necessary to place the sac and tissues back into the skull and close the opening. Often, an implant is used to repair the bony defect so that the tissues do not reherniate. Multi-stage corrective surgery may be necessary, depending upon the location of the encephalocele and structures involved.
Generally, a baby is given at least a few days to adjust to life outside the womb before surgery is performed. Most surgery is done between birth and four months of age. The timing of the surgery depends upon the size, location, assorted other anomalies, as well as whether or not the sac is covered with skin. If the surgical correction isn't urgent, the baby will be evaluated for any other problems pre-surgery.
Babies who have an encephalocele with hydrocephalus may have a shunt placed during surgery to drain off any excess cerebrospinal fluid.
If the encephalocele is too large, or other anomalies are too great, palliative care may be offered to the parents.
What is Palliative Care?
Palliative care is supportive care - food, comfort, and oxygen as needed. Surgery is not performed, and the baby does not receive any life-support. Many of these babies go home on hospice care.
What Happens After Surgery For The Encephalocele?
After surgery, the recovery will vary with the age of the baby, the extent of the repair, and time spent in surgery. Most babies need some help with breathing and may be given supplemental oxygen or an endotracheal tube (a tube passed between the two vocal cords into the trachea) attached to a ventilator.
Babies will come out of surgery with IV lines. These may be placed in the umbilical cord, the scalp, arms, hands, or feet.
Some babies will require TPN - total parenteral nutrition - if the baby is not able to eat.
Common Complications with Encephalocele:
Meningititis is a post-operative concern, so antibiotics will be administered before and after surgery.
Hydrocephalus and shunting is often necessary to prevent build-up of cerebrospinal fluid.
Blindness may occur in babies who survive encephaloceles as the vision center is located in the back of the brain.
Hidden encephaloceles in the front of the skull (Occulta encephaloceles) may cause problems later in life if brain tissue herniates through the bony defect.
Prognosis for Babies With Encephalocele:
Encephaloceles affect about 375 babies yearly in the United States - 20% of babies who have encephaloceles are stillborn. Babies with an encephalocele stand a one in five chance at survival. 21% of babies with an encephalocele survive birth. Of those that are born alive, only half survive.
Location of the encephalocele plays a major factor in prognosis of the birth deffect. Frontal encephaloceles have a 100% survival rate, whereas encephaloceles located on the back of the head are associated with a 55% survival rate.
Additional Encephalocele Resources:
National Institute of Neurological Disorders: A fact sheet for encephaloceles. Information is shallow, but comprehensive
National List of Ongoing Clinical Trials for Encephaloceles - an excellent list of current clinical trials for parents of children with encephaloceles.