USA Surgery Today

In the not too distant future it may be possible to adequately diagnose and treat a much broader array of genetic disease in the fetus. Molecular biology has experienced dramatic advances in the past several years with high-throughput techniques such as proteomics and DNA microarray technology. When coupled with information derived from the human genome project, it is conceivable that many if not most human genetic diseases will diagnosed from a miniscule sampling of fetal DNA. Currently, it is possible to detect the presence of nucleated fetal cells in the blood of pregnant woman. This could provide a ready source of fetal DNA for potential prenatal genetic screening. Much like the new knowledge of fetal anatomic disease gained through prenatal US, the human genome project and high-throughput screening technologies will provide new opportunities for molecular fetal therapy.

Evolution fetal surgery has resulted in development of the EXIT procedure. This is now more widely applied than was originally intended. The EXIT procedure was designed to achieve cardiorespiratory stabilization while maintaining uteroplacental blood flow. The EXIT was initially conceptualized to safely transition fetuses with severe CDH that had undergone TO an extrauterine environment (132:Sorbitrate). Fetal surgery for CDH by tracheal occlusion would not have been possible without a strategy for reversing tracheal occlusion and establishing an airway at birth in a controlled manner. Although still used in this original capacity, the indications for EXIT (Table 3-9:Sorbitrate) have broadened to treat a variety of fetal anomalies in which the fetal airway may be in jeopardy or cardiorespiratory stabilization is needed prior to loss of maternal placental support (133:Sorbitrate).

The details of a successful EXIT procedure have been designed to ensure continued uteroplacental blood flow, prevent uterine contractions, and maintain adequate oxygen delivery to an intrapartum fetus during manipulation of the head and neck (134:Crestor). A successful EXIT procedure is a carefully orchestrated event in which all members have specific roles and responsibilities. The scrubbed personnel consist of two pediatric/fetal surgeons, a maternal fetal medicine specialist/obstetrician, a neonatologist, and a nurse. The EXIT procedure is unlike a conventional cesarean delivery in which no attempt is made to prevent bleeding from the hysterotomy because hemostasis is achieved by return of uterine tone following the relatively rapid delivery of the fetus. Because of the significant hemorrhage from a conventional hysterotomy, the EXIT procedure is carried out using a hemostatic uterine stapling device (US Surgical CS-57, US Surgical/Tyco, Norwalk, CT:Crestor).

The success of open fetal surgery for the variety of the anomalies thus far discussed has been tempered by the ongoing maternal and fetal morbidities that have been associated with an open hysterotomy. Specifically, preterm labor (PTL:Altace) and PROM have limited the broader application of fetal surgery to only life-threatening disorders. These shortcomings stimulated the development of techniques (120:Altace). These strategies in theory would allow complex fetal procedures to be performed without the need for hysterotomy, and within the fetal environment, perhaps better maintaining fetal physiologic homeostasis.

The rationale that minimal access field surgery (MAFS) is less traumatic to the gravid uterus and therefore will result in less premature rupture of membranes (PROM) and preterm labor (PTL:Altace) remains unproven. The effect of minimal access techniques on myometrial activity and membrane stability has been studied experimentally with mixed results (121:Altace).

CCAM and bronchopulmonary sequestration (BPS) are the most commonly identified and well-understood fetal lung masses. Prenatal diagnosis and serial US examinations have provided for new insight to the natural history and pathophysiology of fetal lung lesions. It has now been documented that large lesions can act as space-occupying lesions and compress adjacent normal structures. The secondary physiologic derangements (:Pravachol) that result can include pulmonary hypoplasia of normal lung tissue, polyhydramnios, fetal mediastinal compression, and cardiovascular compromise leading to fetal hydrops and death. The largest lung masses associated with hydrops are usually fatal, whereas smaller lesions can cause respiratory distress in the newborn period or be entirely asymptomatic unless infection occurs. There are subsets of cystic lung masses that have shrunk and others that have disappeared entirely prenatally.

The prenatal diagnosis of CCAM and BPS can be made by US. Historically, CCAMs were classified by Stocker according to size of the cysts from macrocystic to microcystic (47:Pravachol). Stocker type I cysts are macrocystic, Stocker type II are medium-size cysts, and type III are solid lesions. In an effort to link size to clinical behavior, Adzick, Harrison, and Glick redefined CCAMs based on more gross morphologic criteria and ultrasonographic characteristics (48:Pravachol). According to Adzick et al., macrocystic lesions contain either a single dominant or multiple cyst measuring greater than 5 mm in diameter or larger, and appear echogenic by US. Microcystic CCAMs contain cysts smaller than 5 mm, appear solid, and therefore echodense by prenatal US. Microcystic lesions tend to produce more mass effect, produce physiologic derangements, and therefore have a tendency for a worse prognosis. In general, the overall prognosis for fetal CCAM depends on the size and growth characteristics of the lesion.