Prerequisites for fetal neurosurgery: management of central nervous system anomalies toward the 21st century.

With the dramatic technical advances in neuroimaging, it has become possible to diagnose central nervous system (CNS) anomalies in the fetus in utero with more precise morphological analysis. A new technique, high-resolution magnetic resonance (MR) imaging using heavily T2-weighted fast spin echo sequences, has been reported to solve motion artifact of the fetus. However, it has also been recognized that the morphological fetal CNS findings detected in early development are not always the final features: occasionally they may not be determined in diagnosis and may change developmentally or chronologically during the fetal life in utero. Certain factors of the fetal chronology of CNS anomalies can cause irreversible changes during fetal life. These include: (1) significant delay in the neuronal maturation process in fetal hydrocephalus developed in clinicoembryological stage II in the Perspective Classification of Congenital Hydrocephalus (PCCH), (2) secondary neural injury in the intactly developing spinal cord above the neural placode in fetus with spina bifida aperta (myeloschisis), (3) histological "evolution" of tumors or dysgenetic CNS, and (4) deformity of the normally developed intracranial or intraspinal CNS structures. Considering the current status of fetal surgery in general and technical advances promising improved outcomes, fetal neurosurgery can also be applied in the above-mentioned progressive pathology or pathophysiology in the fetal CNS. However, since the failure of the first trial of fetal neurosurgery in the 1980s, the prerequisites have still not been clarified. In order to use advanced neurosurgery techniques in the management of fetal CNS anomalies, these prerequisites have to be established.