Paediatrics: Congenital abnormalities

Congenital abnormalities

There are many disorders that can affect the brain. The majority are classed as disorders of neuronal migration or cortical dysplasia and are thought to either be genetically programmed, due to gene mutation, or a disruption of foetal development due to a deleterious process between the 6th and 16th week of pregnancy, e.g. vascular or viral. They are nor-mally associated with developmental delay, may have a cerebral palsy, and can have very troublesome epilepsies.

Investigation

This is normally initiated after an abnormality is licked up on standard MRI scan of the head. Unless the disorder is likely to have been caused by a single process, e.g. mutation in the Lis1 gene causing the majority of children with isolated lissencephaly, then it is important to perform a full examination and look for other stigmata of a genetic or acquired disorder. For example, dysmorphic features, for the former, and stigmata of infec-tion for the latter.

Most children will benefit from exact radiological classification of the abnormality, and associated changes on examination/history, then tar-geted genetic investigation. If this fails, then karyotype and micro array analyses should be undertaken.

Lissencephaly ‘smooth brain’

There is absence of normal gyri on the cerebral cortex (Fig. 14.1). The children may have unusual facial appearance, difficulty swallowing, failure to thrive, seizures, and severe learning disability. Hands, fingers, or toes may be deformed. It may be associated with other diseases including, Miller-Dieker and Walker-Warburg syndromes. Where multiple genes are deleted, e.g. Miller-Dieker, then wider malformations are seen. In isolated lissencephaly, the majority will either have a change within the Lis1 gene, or it is completely lost (Miller-Dieker).

Pachygyria

Here, there is a paucity of gyri vs the absence in lissencephaly. Although milder, it is associated with a very similar range of complications and man-agement is similar.

Heterotopia

In these disorders there is abnormal positioning of the white/grey matter (Fig. 14.2). It is more commonly used to describe abnormal migration of grey matter. It can be a single area, multiple, nodular or a band. Milder than either of the above, many children will be normal, or present later in life with events such as new onset seizures.

Cortical dysplasias

These can occur as either a very small or large lesion. Either can be associ-ated with learning difficulties, and especially seizures. One in particular is very well recognized—perisylvian polymicrogyria—which is associated with very troublesome seizures and bulbar difficulties. There is a particular type of cerebral palsy which primarily affects the bulbar muscles (unlike diple-gias, hemiplegias and quadripleagias, where bulbar signs are normally much milder than those in the limbs. It is known as Worster-Drought syndrome.

Agenesis of the corpus callosum

Can occur as an isolated finding, or in more widespread disorders, e.g. Aicardi Syndrome. It is isolated, children may be almost normal, but as in other disorders there is a significant chance of learning difficulties, and especially seizures.