Overdistention of the neural tube causes congenital heart disease.

Congenital heart disease consists of cardiac anomalies that originated before or during the truncus arteriosus stage. The central nervous system, serving all organs, is the first to develop. It is the only organ possessing a third circulation. Immediately after the neural tube closes at the fourth week, its lining of immature ependymal cells secretes a proteinaceous neural tube fluid (NTF) at a pressure higher than the amniotic pressure. The resulting distention helps to shape not only the embryonic brain and spinal cord but also the bordering mesodermal cells that later will form vertebrae. The choroid plexus does not begin to secrete true cerebrospinal fluid until two weeks later. Should hypersecretion occur during this critical two week interval, the neural tube will overdistend and allow NTF to infiltrate into mesoderm (Fig. 1). Here, this fluid with its extraneous protein, may damage cells that are destined to form the anlagen of mesodermal organs such as the heart. It may also damage the primitive gut resulting in pulmonary, gastrointestinal and genitourinary anomalies. The most convincing evidence that the neural tube had been overdistended is the combination of anterior and posterior spina bifida that constitutes bilateral hemivertebrae. Vertebral anomalies are present in congenital heart disease though scarcely recognizable on the chest film of the newborn.