- Congenital cystic adenomatoid malformation is the most common congenital cystic lung malformation, but is overall quite uncommon.The antenatal ultrasound classification was proposed by Adzick et╯al:2
◗ type 1—macrocystic, with cysts >5mm, has a good prognosis; and
◗ type 2—microcystic, with cysts <5mm, has a solid appearance and has a
poor prognosis.
While antenatal ultrasound scanning is extremely sensitive, it has poor correlation with histology and it is difficult to estimate prognosis for antenatal counselling - DIFFERENTIAL DIAGNOSIS
The differential diagnoses include:
◗ congenital cystic lung malformations:
• pulmonary sequestration,
• hybrid lesions (elements of both CCAM and sequestration), - congenital lobar emphysema,
• bronchogenic cysts;
◗ congenital high airway obstruction syndrome;
◗ congenital diaphragmatic hernia;
◗ tumours:
• pleuropulmonary blastomas,
• bronchopulmonary alveolar carcinomas, and
• fetal lung interstitial tumours - ASSOCIATED ABNORMALITIES
Poor prognostic signs include bilateral cystic adenomatoid malformations, hydrops fetalis and hypoplastic lungs (lung-to-thorax ratio of <0.25). Polyhydramnios and mediastinal shift are not associated with a poor
prognosis. Cloutier et al4 reported that 18% of patients had associated anomalies such as renal agenesis, cardiac anomalies and pectus excavatum. With increased detection of even smaller lesions, this proportion may now be significantly decreased.
CONSEQUENCES
Respiratory insufficiency can occur if there is associated pulmonary hypoplasia or pleural effusions. Babies with congenital cystic adenomatoid malformations have an increased risk of pneumothorax. Part of the justification for the early resection of cystic adenomatoid malformations is that some may undergo malignant change. In infants and young children, pleuropulmonary blastomas occur and in older children and adults bronchopulmonary alveolar carcinomas dominate. Pleuropulmonary blastomas are difficult to differentiate clinically, radiographically and pathologically from type 4 cystic adenomatoid malformations. This adds further to the argument that all cystic pleuropulmonary blastomas progress from large cysts to more solid
tumours, the prognosis deteriorates.
Cystic adenomatoid malformations can become infected and present as lung abscesses, recurrent pneumonia or empyema. The most common presentation outside the neonatal period is infection.
MANAGEMENT—ANTENATAL
Regular antenatal ultrasound scans should be performed to monitor the size of the lesions and, if large, to monitor for hydrops fetalis. The natural course is for continued growth until 28 weeks and then regression with decreasing size.
Fetal echocardiography could be considered to look for cardiac abnormalities and cardiac function (hydrops fetalis). Magnetic resonance imaging (MRI) could be considered for further differentiation of the lesion.
Ten percent of cystic adenomatoid malformations need fetal intervention. Polyhydramnios may be improved by a simple amniotic fluid reduction or a thoraco-amniotic shunt. The development of hydrops fetalis
may signal the need to consider premature delivery at 30–32 weeks with postnatal resection of the adenomatoid lesion. Antenatal corticosteroids have been shown to resolve hydrops and improve both fetal and postnatal survival without decreasing the size of the lesion. - Larger lesions or lesions with other associated abnormalities should be delivered in a tertiary centre. Smaller lesions can be delivered in the referring centre. If the cystic adenomatoid malformation is uncomplicated,
there is no indication for delivery by caesarean section. Antenatal consultation with a paediatric surgeon should be considered, particularly if the lesion is large or does not regress.
MANAGEMENT—POSTNATAL
The immediate postnatal management depends on the degree of respiratory distress after birth. Respiratory compromise may require intubation and mechanical ventilation. Any respiratory compromise requires immediate referral to a paediatric surgeon for investigation and management. A chest X-ray (CXR) is the usual first-line investigation. . However, a normal chest X-ray is not evidence the lesion has resolved. Over half of those whose antenatal ultrasound and postnatal chest X-ray appeared to show resolution of the lesion had a cystic adenomatoid malformation detectable on computed tomography (CT) scan or required surgery.
If there is no respiratory compromise, the baby can be referred for outpatient follow-up. A CT scan of the chest would usually occur at one month of age. This confirms the diagnosis and delineates the vasculature for
surgery. - There is consensus that all symptomatic cystic adenomatoid malformations should be resected. The management of asymptomatic lesions remains controversial. Some continue to manage conservatively with
regular outpatient CT scans (which carries the unwanted effect of radiation exposure). Expectant management may be appropriate in those with small lesions (either <3cm or <25% of ipsilateral lung volume). Others would resect by 6–12 months of age because of the risk of infection and malignant
change as well as the chance of compensatory lung growth following resection. Resection when asymptomatic may result in fewer complications and shorter hospital stay
Dr. Jayaprakash
Superintendent, ICH.
Institute of Child Health.
Gov. Medical College Kottayam.
Kerala, India.