Approach Considerations
Therapy for fetal congenital pulmonary airway malformation (CPAM) depends on the size of the lesion, its physiologic consequences, and its cystic features. [4] The presence of fetal abnormalities in addition to CPAM has traditionally been a contraindication for intervention, but this may be changing, now that therapy has become less invasive. [3]
Until the mid-2000s, the only options for treatment of microcystic lesions resulting in hydrops were (1) fetal resection if hydrops developed prior to 32 weeks’ gestation and (2) ex-utero intrapartum treatment (EXIT)–to–neonatal resection if hydrops developed after 32 weeks. [6] This paradigm changed after the serendipitous discovery that short courses of maternal steroids seemed to be much more effective than surgery in reversing hydrops. [3, 44, 45]
Macrocystic lesions that cause hydrops can be treated with catheter-based drainage techniques of the dominant cyst. Simple aspiration of the cyst is usually a temporizing measure but can slow down disease progression and help determine if thoracoamniotic shunting will be effective. [27] In lesions without a significant solid component, placement of a thoracoamniotic shunt can effectively decrease the CPAM volume ratio (CVR) and reverse hydrops. [6]
Fetal Resection
An extended Pfannenstiel or lower midline incision is made across the maternal abdomen. The uterus is exposed, and a hysterotomy is made with the aid of intraoperative ultrasonography (US) to delineate fetal and placental position.
Two large absorbable monofilament sutures are placed parallel to the putative hysterotomy. The uterus is then incised, and a cutting stapler that utilizes Lactomer absorbable staples (US Surgical Corporation, Norwalk, CT) is inserted into the uterine cavity and fired. This forms a hemostatic hysterotomy and fixes the amniotic membranes to the myometrium. A fetal cocktail of analgesics and paralytics is then administered intramuscularly (IM).
The fetal thorax is exposed through the hysterotomy, and a thoracotomy is made in the fifth intercostal space. Once the fetal chest is opened, the lesion is usually obvious and will actually deliver itself into the operative field because of increased intrathoracic pressure.
The lesion is then dissected away from normal lung and isolated on its vascular and airway pedicles. These pedicles are ligated and the lesion is removed (see the image below).
The fetal thorax is closed, and the fetus is replaced into the uterus along with warm antibiotic containing lactated Ringer solution. The hysterotomy and the Pfannenstiel incision are then closed in the standard fashion.
Tocolysis with intravenous (IV) magnesium is initiated as soon as maternal anesthesia is withdrawn. [9]
EXIT Procedure
If an EXIT procedure is being done on a nonemergency basis, an amniocentesis can be performed to determine lung maturity, and steroids can be administered, as necessary.
The fetus is accessed via maternal laparotomy and hysterotomy. Specially designed hemostatic staplers are used to avoid uterine bleeding. The head, neck and thorax of the fetus are then delivered, and the fetus is intubated (see the image below). The umbilical cord is kept warm and moist, and the uterine cavity is continuously irrigated with warm saline. The CPAM is then resected by a pediatric surgeon through a thoracotomy.
Once the chest is closed, the umbilical cord is clamped and cut, and the neonate is resuscitated by the neonatologist. [4, 40]
Complications
Catheter-based therapies
Maternal and fetal trauma due to trocar and shunt placement are rare but have been reported [46] ; these include both vascular and structural injuries. In addition, shunts can migrate into a nontherapeutic location, neccesitating another intervention; this tends to happen more often with the smaller and flimsier Harrison shunt than with the Rocket shunt. Shunt insertion can also cause premature rupture of membranes, preterm labor, and chorioamnionitis.
Fetal resection
Possible complications during and after fetal CPAM resection are significant for both the mother and fetus. Maternal complications include bleeding, infection and wound issues. Uterine rupture is a risk after the hysterotomy and necessitates cesarean delivery for the fetus with CPAM and for any subsequent pregnancies. For the fetus, the physiologic stress of the operation is significant, and perioperative fetal demise is not infrequent. Subsequent chest wall deformity is also possible.
EXIT procedure
Blood loss and wound infections are the most common maternal complications with the EXIT procedure. [40] Long-term maternal fertility does not appear to be affected.
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Sonographic images of fetal congenital pulmonary airway malformation. (A) Microcystic congenital pulmonary airway malformation, with ultrasound showing a solid echogenic mass. (B) Macrocystic congenital pulmonary airway malformation, with one or more cysts >5 mm.
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Diagram of cystic lung mass compressing the lung and displacing the mediastinum. Illustration by Colin Fahrion, University of California-San Francisco.
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Congenital pulmonary airway malformation resection.
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Ex-utero intrapartum treatment (EXIT) procedure.
