A congenital cystic adenomatoid malformation (CCAM) is a benign lung lesion appearing as a cyst or lump in the chest that can vary in size. It is the most common type of fetal lung lesion. A large cyst is called a macrocystic lesion, and small cyst is called microcystic.
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Early diagnosis and close monitoring are extremely important because CCAM may have serious implications for the health of the mother. If the fetus develops hydrops, or massive fluid retention, the mother may "mirror" the sick fetus, becoming ill with signs of preeclampsia. Fetal surgery does not cure the preeclamptic state, and mothers must be carefully monitored for signs and symptoms of the maternal mirror syndrome.
CCAM is diagnosed prenatally when an ultrasound shows a cystic or solid lung tumor. Type I and II CCAMs appear as cystic, fluid-filled masses while Type III appears as a solid mass.
CCAM can be confused with a bronchopulmonary sequestration (BPS), which may also present as a solid mass. However, a bronchopulmonary sequestration always has a systemic arterial blood supply from the aorta while a Type III congenital cystic adenomatoid malformation does not.
Large left-sided CCAM in fetal chest. © CHOP/CFDT
Therefore, a color flow Doppler ultrasound showing a systemic arterial blood supply to the mass confirms the diagnosis of bronchopulmonary sequestration. Recently, we have described a hybrid lesion, which consists of both CCAM and BPS lesions.
Prenatal diagnosis provides insight into the in utero evolution of fetal lung lesions such as CCAM, BPS and congenital lobar emphysema. Serial sonographic study of fetuses with lung lesions has helped clinicians to define the natural history of these lesions, determine the pathophysiologic features that affect clinical outcome and formulate management plans that are based on prognosis.
Families who come to Children’s Hospital of Philadelphia's Center for Fetal Diagnosis and Treatment for an evaluation of a fetal mass undergo a Level II ultrasound using power Doppler and three-dimensional (3-D) reconstruction.
This level II ultrasound shows a macrocystic CPAM. © CHOP/CFDT
These techniques also enable us to differentiate between CCAM and BPS. A new technique using ultrafast MRI is performed to document lung volume, which helps to confirm the diagnosis. A fetal echocardiogram rules out any structural heart abnormalities. The family then meets with the pediatric surgeon to discuss options. If hydrops is not present, close surveillance will be provided to the family with a telephone call and follow-up letter to the referring physician.
CCAM volume ratio (CVR)
Recently, we have measured fetal CCAM volume by sonographic measurement using the formula for a prolate ellipse (length X height X width X 0.52). A CCAM volume ratio (CVR) is obtained by dividing the CCAM volume by head circumference to correct for fetal size. A CVR > 1.6 is predictive of increased risk of hydrops with 80 percent of these congenital cystic adenomatoid malformation fetuses developing hydrops.
The CVR may be useful in selecting fetuses at risk for hydrops. These babies will require close ultrasound observation and possible fetal intervention. Thirty serial CVR measurements have shown that CCAM growth usually reaches a plateau by 28 weeks gestation. For fetuses at less than 28 weeks, the recommendation is twice weekly ultrasound surveillance if the CVR > 1.6 and initial weekly surveillance for fetuses with smaller CVR values.
If hydrops is present, our team will sit down with your family to explain fetal surgery in detail. Patient education materials are provided and families have the opportunity to tour the Newborn/Infant Intensive Care Unit (N/IICU).
Families may choose to terminate the pregnancy, let nature take its course or undergo fetal surgery. However, fetal surgery is only an option once hydrops develops.
In our experience with several hundred fetal lung lesions, CCAM and BPS are not associated with an increased incidence of chromosomal anomalies. Therefore, amniocentesis and chorionic villus sampling (CVS) are not necessary prerequisites for fetal surgery.
If hydrops does not develop, appropriate delivery plans will be made, depending upon the size of the lesion. For example, if a CCAM lesions shrinks in size, which occurs in approximately 10 to 20 percent of cases, delivery at a local hospital is certainly possible. Approximately two-thirds of bronchopulmonary sequestration lesions will shrink before birth, and some of these will not require post-natal resection.
If the lesion remains moderate to large, we recommend delivery at a center that can provide extracorporeal membrane oxygenation (ECMO), and because the newborn may require emergent removal of the tumor or mass, the availability of a pediatric surgeon is crucial.
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For small lesions, we recommend follow-up at a few weeks of age when a cine or spiral chest CT can be performed followed by elective resection of the mass. Regardless of size, the mass should be removed due to risks of infection and malignant degeneration.
The finding that fetuses with hydrops are at very high risk for fetal or neonatal demise led to the performance of either fetal surgical resection of the massively enlarged pulmonary lobe (fetal lobectomy) for cystic/solid lesions or thoracoamniotic shunting for lesions with a dominant cyst. Lesions with associated hydrops that are diagnosed late in gestation may benefit from resection using an ex utero intrapartum therapy (EXIT) approach. The fetus with a lung mass but without hydrops has an excellent chance for survival with maternal transport, planned delivery, neonatal evaluation and surgery.
After a fetal or neonatal lobectomy. © CHOP/CFDT
Neonates with respiratory compromise due to a cystic lung lesion require prompt surgical resection, usually by lobectomy. In the most severe cases, ventilatory support with high-frequency ventilation or ECMO may be required. In asymptomatic neonates with a cystic lung lesion, we believe that elective resection is warranted due to the risks of infection and occult malignant transformation.
Malignancies consist mainly of pulmonary blastoma and rhabdomyosarcoma in infants and young children, and bronchioloalveolar carcinoma in older children and adults. After confirmation of CCAM location by postnatal chest CT scan with intravenous contrast, we recommend elective resection at 1 month of age or older. Our experienced pediatric surgeons can safely perform a thoracotomy and lobectomy in infants with minimal risk of morbidity, and thoracoscopic resection has been performed. Early resection also maximizes compensatory lung growth; long-term follow up has shown normal pulmonary function.
In 1998, we reported a series of more than 175 prenatally diagnosed cases from Children's Hospital of Philadelphia and found the prognosis depends on the size of the lung mass and secondary physiologic derangement. These findings have been confirmed in several hundred fetal lung lesion cases referred to us since 1998. A large mass causes mediastinal shift, hypoplasia of normal lung tissue, polyhydramnios and cardiovascular compromise leading to fetal hydrops and death.
Huge fetal lung lesions have reproducible pathophysiologic effects on the developing fetus. Esophageal compression by the thoracic mass causes interference with fetal swallowing of amniotic fluid and results in polyhydramnios. Polyhydramnios is a common obstetrical indication for ultrasonography; therefore, a prenatal diagnostic marker exists for many large fetal lung tumors. Support for this concept comes from the absence of fluid in the fetal stomach in some of these cases and the alleviation of polyhydramnios after effective fetal treatment.
Hydrops is secondary to vena caval obstruction and cardiac compression from large tumors causing an extreme mediastinal shift. Like CCAMs, a fetal bronchopulmonary sequestration can also cause fetal hydrops, either from the mass effect or from a tension hydrothorax that results from fluid or lymph secretion from the bronchopulmonary sequestration. Hydrops is a harbinger of fetal or neonatal demise. It manifests as fetal ascites, pleural and pericardial effusions, and skin and scalp edema. Although there is some association of both polyhydramnios and hydrops with fetal lung lesions, experience indicates that either can occur independently of the other. Smaller thoracic lesions can cause respiratory distress in the newborn period, and the smallest masses may be asymptomatic until later in childhood when infection, pneumothorax or malignant degeneration may occur.
Large fetal lung tumors may regress in size on serial prenatal sonography, illustrating that improvement can occur during fetal life. In particular, many cases of non-cystic BPS dramatically decrease in size before birth and may not need treatment after birth. However, fetal lung lesions that seem to disappear on prenatal ultrasound and are not seen on neonatal chest radiograph still require evaluation by chest CT scan, which will frequently detect a lesion.
Updated: June 2011