Sonographic guidance can be used to permit therapy with a shunt, radiofrequency ablation needle, or angioplasty catheter. With these procedures, desired instruments cross the maternal abdominal wall, uterine wall, and membranes to reach the amnionic cavity and fetus. Risks include maternal infection, preterm labor or prematurely ruptured membranes, and fetal injury or loss.
A shunt placed from the fetal pleural cavity into the amnionic cavity may be used to drain pleural luid (Fig. 16-7). A large efusion may cause a significant mediastinal shift, resulting in pulmonary hypoplasia or in heart failure and hydrops. he most common etiology of a primary efusion is chylothoraxcaused by lymphatic obstruction. Pleural efusions may also form secondary to congenital viral infection or aneuploidy, or they may be associated with a malformation such as pulmonary
FIGURE 16-7 Thoracoamnionic shunt placement. A. A large, right-sided fetal pleural effusion (asterisks) and ascites were identified at 18 weeks' gestation. The effusion was drained but rapidly reaccumulated. The xanthochromic fluid contained 95-percent lymphocytes, consistent with chylothorax. B. A double-pigtail shunt (arrow) was inserted under ultrasound gUidance. Following shunt placement, the efusion and ascites resolved.
FIGURE 16-8 Vesicoamnionic shunt placement. A. After amnioinfusion is performed, a trocar is inserted into the distended fetal bladder under sonographic guidance. The pigtail catheter is threaded into the trocar. B. The double-pigtail shunt has been deployed down the trocar, and the trocar has been removed. The distal end of the shunt is coiled within the fetal bladder, and the proximal end is draining into the amnionic cavity. (Reproduced with permission from Shamshirsaz AA, Ramin, SM, Belfort MA: Fetal therapy. In Yeomans ER, Hoffman BL, Gilstrap LC III, et al: Cunningham and Gilstrap's Operative Obstetrics, 3rd ed. New York, McGraw-Hili Education, 201o7.) sequestration. Yinon and associates (2010) reported aneuploidy cent of cases.
Typically, the efusion is first drained using a 22-gauge needle with sonographic guidance. Tests for aneuploidy and infection are performed, as well as a cell count. A pleural-fluid cell count with greater than 80-percent lymphocytes, in the absence of infection, is diagnostic of chylothorax. If the luid reaccumulates, a trocar and cannula may be inserted through the fetal chest wall, and a double-pigtail shunt may be placed to drain the efusion. If the efusion is right-sided, the shunt is placed in the lower third of the chest to permit maximum expansion of the lung. If left-sided, the shunt is placed along the upper axillary line to allow the heart to return to normal position (Mann, 2010). he overall survival rate is 70 percent, and that for hydropic fetuses approximates 50 percent (Mann, 2010; Yinon, 2010). Shunt displacement into the amnionic cavity is not uncommon. If the shunt remains in place, it must be clamped immediately upon delivery of the newborn to avoid pneumothorax.
Shunts can also drain a dominant cyst in fetuses with macrocystic congenital cystic adenomatoid maormation. However, cysts rarely are large enough to pose a risk for hydrops or pulmonary hypoplasia. Shunt placement may improve survival to 90 percent in the absence of hydrops and to more than 75 percent with hydrops (Liwinska, 2017).