Brain malformations

Septo-optic dysplasia (de Morsier syndrome)

Septo-optic dysplasia (De Morsier syndrome) is a developmental defect of the forebrain that develops toward the end of the first month of gestation and involves hypoplasia of the optic nerve, absence of the septum between the anterior parts of the two lateral ventricles, and deficiency of pituitary hormones. Although the causes may be multiple, abnormalities in one specific gene (HESX1) have been found in some patients with septo-optic dysplasia.

Symptoms may include decreased visual acuity in one or both eyes, nystagmus, strabismus, and endocrine dysfunction (including growth hormone deficiency, hypothyroidism, adrenal insufficiency, diabetes insipidus, and hypogonadism). Seizures may develop. Although some children have normal intelligence, others have learning disabilities, mental retardation, cerebral palsy, or other developmental delays. Diagnosis is based on MRI. All children diagnosed with the disorder should be evaluated for endocrine dysfunction and developmental disorders. Treatment is supportive.

Anencephaly

Anencephaly is the absence of the cerebral hemispheres. The missing brain is sometimes replaced by malformed cystic nerve tissue, which may be exposed or covered by skin. Parts of the brainstem or spinal cord may be missing or malformed. The baby is stillborn or dies within days or weeks. Treatment is supportive.

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Encephalocele

An encephalocele is a protrusion of nerve tissue and meninges through a defect in the skull. The defect is caused by incomplete closure of the cranial vault (cranium bifidum). Encephaloceles usually occur in the midline and the protrusion occurs anywhere from the back of the head to the nasal openings, but may be asymmetrical in the frontal and parietal regions. A small protrusion may resemble a cephalohematoma, but an X-ray will show a defect in the skull at its base. Hydrocephalus is often seen with encephalocele. About 50% of children have other congenital anomalies.

The prognosis, which depends on the location and size of the herniation, is usually good. In most cases, encephaloceles can be successfully operated on. Even if large, the herniation usually contains predominantly ectopic neural tissue, which can be removed without deteriorating functional capabilities. If encephaloceles are associated with other severe developmental anomalies, the decision to perform surgery may be more difficult.

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Malformed cerebral hemispheres

The cerebral hemispheres may be large, small, or asymmetrical; the convolutions may be absent, unusually large, or numerous and small; microscopic examination of the apparently normal brain may reveal disorganization of the normal arrangement of neurons. Microcephaly, moderate to severe motor and mental retardation, and epilepsy are common with these defects. Treatment is supportive, including anticonvulsants as needed to control seizures.

Holoprosencephaly

Holoprosencephaly occurs when the embryonic prosencephalon (forebrain) fails to segment and diverge. The forebrain, skull, and face are abnormally formed. This malformation can be caused by defects in the sonic hedgehog gene. If severe, the fetus may die before birth. Treatment is supportive.

Lissencephaly

Lissencephaly consists of an abnormally thickened cortex, decreased or absent differentiation into layers, and diffuse heterotopia of neurons. It is caused by a defect in neuronal migration, the process by which immature neurons connect with radial glia and move from their origin near the ventricles to the surface of the brain. Several defects in individual genes can cause this malformation (eg, LIS1). Children with this malformation have mental retardation, muscle spasms, and seizures. Treatment is supportive, but many children die before age 2.

Polymicrogyria

Polymicrogyria, in which the convolutions are small and numerous, is thought to result from brain damage between the 17th and 26th weeks of gestation. Mental retardation and seizures may occur. Treatment is supportive.

Porencephaly

Porencephaly is a cyst or cavity in a cerebral hemisphere that communicates with a ventricle. It may develop prenatally or postnatally. The defect may be caused by a developmental defect, an inflammatory process, or a vascular complication such as intraventricular hemorrhage with extension into the parenchyma. Neurological examination findings are usually abnormal. The diagnosis is confirmed by CT, MRI, or ultrasound of the brain. Rarely, porencephaly causes progressive hydrocephalus. The prognosis is variable; a small number of patients develop only minimal neurological signs and have normal intelligence. Treatment is supportive.

Hydranencephaly

Hydranencephaly is an extreme form of porencephaly, in which the cerebral hemispheres are almost completely absent. Usually, the cerebellum and brainstem are normally formed, the basal ganglia are intact. The meninges, bones and skin over the cranial vault are normal. Hydranencephaly is often diagnosed prenatally by ultrasound. The results of the neurological examination, as a rule, differ from normal, the child develops with disorders. Externally, the head may look normal, but when transilluminated, light shines through completely. CT or ultrasound confirms the diagnosis. Treatment is supportive, with shunting in case of excessive growth of the head size.

Schizencephaly

Schizencephaly, which can be classified as a form of porencephaly, results from the formation of abnormal convolutions or clefts in the cerebral hemispheres. Unlike porencephaly, which is thought to result from brain damage, schizencephaly is thought to be a defect in neuronal migration and thus a true malformation. Treatment is supportive.