The face and forebrain (or prosencephalon) of an embryo normally begin to develop in the 5th and 6th weeks of pregnancy. If the forebrain fails to divide into normal right and left hemispheres, deformities in the face and brain, or holoprosencephaly, results.
Types of Holoprosencephaly
The most serious form is alobar holoprosencephaly, in which the hemispheres completely fail to separate. It is characterized by severe facial and brain abnormalities so profound that they often cause intrauterine death. In semilobar holoprosencephaly the brain's hemispheres develop only a slight separation. Lobar holoprosencephaly is marked by substantial, but still incomplete, separation of the hemispheres.
Causes of Holoprosencephaly
The cause of most cases of holoprosencephaly is unknown. Nearly half of all cases are linked to chromosomal factors, such as Patau's syndrome (trisomy 13) and Edwards' syndrome (trisomy 18). There appears to be an increased risk for holoprosencephaly in infants of diabetic mothers, but the significance of this is not well understood.
Signs and Symptoms of Holoprosencephaly
The most severe forms of holoprosencephaly produce seizures and mental retardation. Typical facial defects involve the eyes, nose, and upper lip. In some cases, the nose may be missing entirely or may develop above the eye in the form of a proboscis, a tubular appendage. Other facial anomalies include:
- ethmocephaly (rare): absent nose; a proboscis separates narrow-set, sometimes abnormally small, eyes
- cebocephaly: small, flattened nose with a single nostril beneath incomplete or underdeveloped narrow-set eyes
- premaxillary agenesis median (cleft lip)
- cyclopia: single eye located in the area normally occupied by the root of the nose
Treatment for Holoprosencephaly
Treatment is largely symptomatic.
Prognosis for Infants with Holoprosencephaly
Infants born with most forms of holoprosencephaly face a poor prognosis. Few who survive achieve significant mental development.
Iniencephaly is marked by extreme backward bending (retroflexion) of the head and severe spinal defects. Iniencephalic infants are short, with disproportionately large heads.
Signs and Symptoms of Iniencephaly
Usually, the neck is absent, with the skin of the face connected directly to the skin of the chest and the scalp connected to the skin of the back. Other anomalies also may be present, such as anencephaly, cephalocele (part of the cranial contents protrude from the skull), hydrocephalus, cyclopia, absent lower jaw bone, cleft lip/palate, cardiovascular disorders, diaphragmatic hernia, and gastrointestinal abnormalities.
Diagnosis of Iniencephaly
The condition is readily diagnosed at birth by the prominence of its symptoms.
Prognosis for Infants with Iniencephaly
Newborns with iniencephaly seldom live more than a few hours. The mother is at risk during pregnancy and the birthing process because the distorted fetal body can cause her serious injury.
Lissencephaly means smooth brain. It is a rare disorder marked outwardly by abnormal smallness of the head (microcephaly) and inwardly by the lack of normal folds and grooves in the surface of the brain.
Cause of Lissencephaly
Lissencephaly results when nerve cells in the fetal neural tube fail to move to the proper location (called defective neuronal migration) as the fetus's central nervous system develops. This may be caused by intrauterine or fetal viral infections during the 1st trimester, insufficient blood supply to the brain early in pregnancy, or a genetic disorder.
Signs and Symptoms of Lissencephaly
Babies born with lissencephaly may present with an unusual facial appearance, difficulty swallowing, severe psychomotor retardation, muscle spasms, seizures, and/or deformities of the hands, fingers, or toes.
Diagnosis of Lissencephaly
The condition is diagnosed at or soon after birth. Doctors usually confirm the diagnosis with ultrasound, computed tomography (CT scan) or magnetic resonance imaging (MRI scan).
Treatment for Lissencephaly
Treatment for lissencephaly is symptomatic, depending on the nature and severity of the brain malformations. Supportive care and nursing may be needed. Medication may be prescribed to control seizures, and a shunt may be required to control hydrocephalus. When swallowing is a problem, a gastrostomy tube may be necessary.
Prognosis for Infants with Lissencephaly
Prognosis depends on the degree of brain malformation. While some have nearly normal development and intelligence, most show no significant development beyond that of a normal child who is 3 to 5 months old. Many lissencephalic children die of respiratory problems before age 2.