Developmental disorders

II./4.1.: Epidemiology

Most developmental anomalies of the lumbosacral region is caused by abnormal closure of the neural tube. These are called neural tube defects.

These abnormalities have either obvious visible local signs at birth, are discovered at a routine ultrasound examination during pregnancy or they may stay hidden causing symptoms with different severity during lifetime (Occult dysraphism).

Two major types of the obvious forms are meningocele and myelomeningocele. The former type is the protrusion of the dura mater and accompanying arachnoid membrane through a defect in the spinal canal due to dysfunctional closure of the neural tube. In myelomeningocele cases the dura and arachnoid membrane, the spinal cord and variably other neural elements are exposed on the infant’s back. The term spina bifida encloses all subtypes of neural tube defects, including the most common type, the occult dysraphism. The incidence of this abnormality is 1-2 in 1000 live births but it shows great geographic and ethnic variability.

Good example for this is that the incidence in the UK is 0.7-2/1000 live births, while in Ireland it’s 5/1000. In the last two decades the incidence of neural tube defects has rapidly reduced. This phenomenon is usually attributed to improving nourishment of pregnant women and wide spread use of perinatal folic acid replacement. A Hungarian study showed that 93% of primary neural tube defects could be avoided by 0.8 mg daily dose of folic acid.