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Congenital Cystic Adenomatoid Malformation / CCAM (recently termed Congenital Pulmonary Airway Malformation / CPAM) of the lung is a relatively rare abnormality that appears on an ultrasound as a solid or cystic mass (tumor) of pulmonary tissue that has an abundance of bronchial structures (breathing channels).
The cause of Congenital Cystic Adenomatoid Malformation (CCAM / CPAM) is unknown.
One theory holds that it is the result of bronchial structures failing to mature properly at approximately the fifth or sixth week of gestation, about the time the lungs begin to form.
Another theory holds that CCAM / CPAM is due to an abnormal growth pattern of lung tissue due to bronchial obstruction.
There is no known genetic cause for CCAM / CPAM, and no cases of recurrence in a sibling or offspring have been reported.
Although Congenital Cystic Adenomatoid Malformation (CCAM / CPAM) is increasingly being diagnosed in utero, the true incidence of this lesion is not known.
A CCAM / CPAM lesion is slightly more common in males than females.
Several classification systems have been used to describe the sonographic appearance of these malformations. Among the most commonly used is an adaptation of Stocker’s histologic classification.
Congenital Cystic Adenomatoid Malformation (CCAM / CPAM) can be detected by a detailed ultrasound using color flow Doppler and by ultrafast fetal MRI to confirm the diagnosis and document size and location of the Congenital Cystic Adenomatoid Malformation.
A fetal echocardiogram can rule out any associated structural heart abnormalities and assess the effect of the Congenital Cystic Adenomatoid Malformation on the heart.
The best prognostic indicator we have is the CVR measurement. The CAM volume is a calculate volume based on ultrasound measurements obtained in three dimensions of the mass at presentation. The volume is then divided by the head circumference so the CAM volume is corrected for gestational age. We are also evaluating the usefulness of fetal lung volumes by MRI testing as a second predictor of prognosis.
If the CVR is < 1. 6, this is a Congenital Cystic Adenomatoid Malformation with a favorable prognosis. The risk of developing hydrops is less than two percent in these cases. The only exceptions are malformations with a "dominant cyst." Dominant cysts are those that comprise greater than one-third of the entire volume of the Congenital Cystic Adenomatoid Malformation. These lesions can enlarge acutely, do not follow a predictable pattern of growth and must be followed closely.
Those congenital cystic adenomatoid malformation with a CVR > 1. 6 are at high risk for the development of hydrops and fetal demise, which occurs in up to 80 percent of cases in this category. Such malformations should be followed with twice-weekly ultrasound scans so that fetal surgery can be undertaken at the earliest signs of hydrops.
All congenital cystic adenomatoid malformation should be followed weekly for measurement of CAM volume and CVR until the growth of CCAM reaches a plateau. The natural history of CCAM is near exponential growth, from 20 weeks gestation until the plateau is reached.
The average gestational age at which the growth plateau is reached is 26 weeks. A fetus does not typically get into trouble from hydrops once the plateau has been reached. From that point on, there is usually a slow decrease in the size of the Congenital Cystic Adenomatoid Malformation, as the baby grows around it.
Congenital Cystic Adenomatoid Malformation should be followed at least weekly with ultrasound scans for measurement of CAM volume. The CAM volume has been shown to be predictive of outcome in fetuses with these malformations.
At least weekly ultrasound scans also are recommended to detect signs of hydrops (in utero heart failure) caused by the Congenital Cystic Adenomatoid Malformation. The development of hydrops in a fetus with a Congenital Cystic Adenomatoid Malformation is usually an indication for fetal surgery.
Another sign of hydrops is placental swelling. If placental swelling develops as a result of the Congenital Cystic Adenomatoid Malformation, the mother is at risk to develop the "mirror syndrome, " an unusual condition in which the mother's health "mirrors" that of the sick fetus by developing swelling and high blood pressure.
This condition calls for immediate delivery of the fetus because "mirror syndrome" is potentially life threatening for the mother.
In contrast, low-risk Congenital Cystic Adenomatoid Malformation with CVRs < 1. 6 who reach a growth plateau can often be delivered without risk of respiratory compromise following delivery.
All high-risk fetuses with CVRs > 1. 6 should be delivered at a tertiary-care hospital, preferably with Extracorporeal Membrane Oxygenation / ECMO (heart / lung machine) capability, and where a skilled surgical staff is on hand for resuscitation of the newborn and emergency removal of the mass.
The hospital should also have an intensive care nursery and staff trained to care for a newborn with potentially severe pulmonary hypoplasia. In rare cases, the size of the Congenital Cystic Adenomatoid Malformation may preclude ventilation after the baby is born or support by ECMO because of shift of the mediastinum.
In these cases, an EXIT (ex utero intrapartum treatment) procedure may be performed to resect the Congenital Cystic Adenomatoid Malformation while on placental support. Another consideration is multicystic Congenital Cystic Adenomatoid Malformation, which may acutely enlarge after delivery due to "air trapping," necessitating an emergency thoracotomy for CCAM removal.
The indications for fetal intervention depend on the type of lesion, whether solid or cystic, and the development of hydrops. In malformations with a dominant cyst, the development of hydrops indicates the need for a thoracentesis or thoracoamniotic shunt to decompress the fluid within the cysts. Thoracentesis alone, however, cannot provide the continuous decompression that thoracoamniotic shunting can. In the rare instances of Congenital Cystic Adenomatoid Malformation (CCAM / CPAM) with a single or a couple of large cysts responsible for hydrops, thoracoamniotic shunting is the treatment of choice.
The first uses of thoracoamniotic shunting in fetuses with CCAM / CPAM were reported in 1987 by Nicolaides and associates and separately by Clark. Percutaneous placement of a thoracoamniotic shunt in a fetus of 20 weeks' gestation decompressed a large type I Congenital Cystic Adenomatoid Malformation, according to Clark, and resolved both the mediastinal shift and hydrops. The infant was successfully delivered at 37 weeks of gestation and then underwent uneventful resection of the CCAM / CPAM. Six subsequent cases of thoracoamniotic shunting in CCAM / CPAM have been reported by Adzick and coworkers, with a good outcome in five of the six fetuses treated, although the survivors had respiratory insufficiency and some have required ECMO or high-frequency ventilation.
A more recent study by Wilson et al found that shunting of macrocystic (type I) CCAM / CPAM resulted in a 51 percent reduction in the CAM volume and resolved the hydrops over seven to ten days. Successful shunting prolonged pregnancy into the third trimester and seven of the ten fetuses treated with thoracoamniotic shunting survived. The authors concluded that a thoracoamniotic shunt should be considered as a treatment option for fetuses with macrocystic (type I) CCAM / CPAM with hydrops or a high risk of developing pulmonary hypoplasia (underdeveloped lungs), and failure of less invasive needle aspiration treatment of the macrocyst fluid (thoracentesis) to prevent rapid reaccumulation of the fluid after one to two aspirations.
Another recent study by Vu et al sought to improve the ability to identify fetuses at especially high risk of developing hydrops because of large CCAM / CPAM. The study focused on large malformations because large size had already been associated with increased risk for developing hydrops. A combination of three features that could be seen by sonogram was associated with hydrops with a large chest mass. These features were: mass-thorax ratio (MTR) of at least 0.56; the predominance of cystic lesions, and inversion or depression of the diaphragm.
With regard to in utero prognosis, poor outcomes are more common in the type III CCAM / CPAM. These microcystic lesions become enlarged, resulting in hydrops and intrauterine fetal demise. In these later cases open fetal surgery and resection are indicated.
High risk CCAM / CPAMs (with a CVP of ≥1.6 or hydrops) should be treated with maternal steroids. We have found that in up to 50 percent of patients, the CCAM / CPAM will stop growing. This allows the baby to grow out of hydrops and for the lungs to develop.
In the case of solid lesions, the development of hydrops manifests by ascites, pleural or pericardial effusions, skin or scalp edema or placentomegaly.
In some cases, maternal steroids appear to arrest the growth of these lesions. This is sometimes a useful temporizing measure. In patients with large, solid CCAM / CPAM with associated hydrops, open fetal surgery is indicated. Without intervention, CCAM / CPAM associated with hydrops is almost always fatal.
In experience with 26 cases of open fetal surgery with hydropic CCAM / CPAM, the survival has been 61 percent. The outcomes for fetal surgery for CCAM / CPAM have been improved by careful observation and by intervention at the earliest signs of hydrops.
In addition, the use of intraoperative echocardiographic fetal monitoring and thoracoabdominal surgical exposure have helped improve outcomes in this surgery. The survival in these cases has increased to 78 percent. Perhaps the best way to improve outcomes in high risk CCAM / CPAM is through close surveillance to identify early signs of hydrops. Too often, patients are referred late in their course presenting with advanced hydrops.
Cases in which CCAM / CPAM are large but have not resulted in hydrops may require resection during an EXIT procedure.
In some cases, the CCAM / CPAM is so sufficiently large that the mediastinum is shifted and the lung compressed. Under these conditions, the lungs may not be able to be ventilated. Removing the CCAM / CPAM during an EXIT procedure allows the lungs to function.
Newborns with CCAM / CPAM should be evaluated in the nursery to confirm the prenatal diagnosis and to exclude other health conditions.
A chest CT scan will confirm the diagnosis and define the anatomy. Complete resection of the CCAM / CPAM is the preferred treatment. The reasons for recommending resection for CCAM / CPAM, which are otherwise asymptomatic, are infection and neoplastic transformation.
All malformations have a connection with the tracheobronchial tree, which may predispose to bacterial contamination. Malformations can undergo malignant transformation. The youngest case reported was a patient only 13 months of age.
While some recommend observation for asymptomatic CCAM / CPAM, we routinely recommend they be resected. These malformations remain a health concern for as long as they are present.
Unfortunately, we do not know how to identify which malformations will become infected or develop a tumor before the problem actually occurs.
The long-term outcome of infants with CCAM / CPAM following resection is excellent. However, if the mass is not fully removed, the child can be at risk for complications, such as air trapped in the residual CCAM / CPAM, which causes gradual enlargement over time, infection and other problems.
Once the mass is removed, the remaining lung tissue will undergo compensatory lung growth to make up for the lung tissue lost to resection. These children live life without any apparent limitations on their activities and with no increased risk of respiratory infections.
Children who survived open fetal surgery for CCAM / CPAM associated with hydrops are still doing well from one to eight years after their procedure.
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