Among the most important lessons learned in invasive fetal therapy were the necessity to understand the natural history of the untreated condition and the ability to identify fetuses most likely to benefit from treatment.
Based on the observation that postnatal shunting for hydrocephalus is beneficial, Birnholz and Frigoletto reported using serial percutaneous cephalocentesis to treat hydrocephalus in utero.
The results of their efforts were disappointing because the fetus had unrecognized intracranial abnormalities and Becker type muscular dystrophy. Shortly thereafter, ventriculoamniotic shunts were developed to provide consistent ventricular decompression.
Although these procedures enjoyed a brief period of enthusiasm, results proved to be poor, often related to undetected central nervous system and non-central nervous-system anomalies, and the shunts failed to provide consistent ventricular decompression because of obstruction or migration.A
The fetus that is likely to benefit from ventriculoamniotic shunting is one with isolated progressive ventriculomegaly. However, the incidence of associated central nervous system anomalies in reported series has varied from 70% to 84%, with many of these defects being undetected prenatally.
Previous studies list the incidence of isolated progressive ventriculomegaly from 0% to 56%, with most reports listing the incidence as only between 4% and 14%. Even with improved diagnostic capabilities, identifying appropriate candidates for fetal surgery and intervention may be difficult.
If ventriculoamniotic shunting is to be reinstated, selection criteria must first be defined. These criteria would include:
- Fetuses with isolated progressive ventriculomegaly
- Accurate exclusion of other central nervous system and extra-central-nervous-system anomalies
- Development of a valved shunt less likely to clog, become dislodged, or cause ventriculitis than previous versions.
In fact, a completely internalized ventriculoperitoneal shunt may have advantages over percutaneous shunting because of because of the limitations associated with percutaneous shunting.
With the increased accuracy of ultra-fast fetal MRI for diagnosing central nervous system abnormalities, the ability to identify isolated rapidly progressive hydrocephalus is better now than ever before. It is not clear, however, that ventricular decompression, even in these highly selected fetuses, will improve the postnatal outcome in these cases.