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Congenital Cystic Adenomatoid Malformation of the Lung (CCAM)


Type 2 CCAM

Type 3 CCAM (Mediast. Shift)

CCAM (Eversion of Diaphragm)

Type 1 CCAM

Percut. Drainiage of CCAM Cyst

Type 2 CCAM

Findings:

This transverse scan through the fetal thorax demonstrates an echogenic mass which displaces the heart across the mediastinum to the right side. This mass is homogenous and solid except for a single small cyst. The mass has the appearance most of a Type III CCAM although a single small cyst would make it a Type II lesion. There is no evidence of hydrops fetalis, polyhydramnios or other congenital anomalies. Likewise, doppler interrogation of the mass, heart, aorta and inferior vena cava demonstrated no evidence of feeding or draining systemic vessels.

Discussion:

Congenital cystic adenomatoid malformation of the lung (CCAM) is a rare pulmonary developmental abnormality which was first described and separated from other cystic lung masses in 1949 by Ch'in and Tang. Since then numerous reports of this abnormality have appeared in the pathologic, pediatric and imaging literature. The lesion has been described pathologically as an overgrowth and increase in the number of terminal respiratory structures without alveolar differentiation, resulting in epithelium-lined cysts of various sizes. This lesion has been divided pathologically by Madewell and Stocker into three distinct types: Type I which has single or multiple large cysts (> 2 cm. [usually 3 - 7 cm]) lined with pseudostratified columnar epithelium, Type II, in which there are multiple small cysts (< 1.5 cm) lined by cuboidal to columnar epithelium and Type III consisting of a mass of cuboidal-lined ciliated epithelium of alveolar like stuctures without macroscopic cysts. For several years the prognosis of CCAM was felt to be related to the type of lesion. In fact, it is now clear that the size and mass effect are of more importance than the specific type.

A number of anomalies have been described as being associated with CCAM: these include bilateral renal agenesis, renal dysplasia, cardiac abnormalities including tetralogy of Fallot, truncus arteriosus and ventricular septal defect, hydrocephalus, jejunal atresia, diaphragmatic hernia, enteric cyst, tracheoesophageal fistula, sirenomelia and vertebral and clavicular abnormalites.

Polyhydramnios is frequently associated with CCAM. It is thought to be due to: impairment of fetal swallowing by compression of the esophagus, loss of protein into the amniotic fluid, secretion or induction of secretion of ADH or to decreased amniotic fluid absorption by the abnormal and compressed lung. Hydrops can develop and is likely due to obstruction of venous return by the expanding mass which also may compress the heart and impair venous return and cardiac output.

Lesions have most often been unilateral, although numerous bilateral CCAMs have been reported. Perhaps the most interesting feature of this entity is its changing appearance throughout gestation. Large masses with significant compressive effect and even hydrops have been described that have regressed throughout gestation. In utero therapies have been sucessful at either draining large macrocysts repeatedly or in utero surgical excision of the affected CCAM. The theory is to prevent hydrops from worsening or to prevent the development of pulmonary hypoplasia. As this lesion has been shown to regress in many cases on its own; intervention should likely be delayed until the earliest sign of hydropic decompensation. A recent analysis of a large number of prenatally diagnosed fetuses with CCAM was reported by Dommergues et al This study had several interesting observations and conclusions. First, depsite experienced examiners, 4 cases were misclassified as CCAM when they were in fact, pulmonary sequestrations. Their course was similar to that of ipsilateral CCAM's. Second, it is clear that the pathological Stocker classification has no utility in the prognosis or management of these patients, as lesions of all types were seen in the complicated and uncomplicated categories.Third, while therapy was sucessful in four patients, it failed in five patients. I believe a large part of the failure is due to the fact that while the lesions may appear to be dominated by large cysts that solid tissue, typical of Type III disease, truly predominates. This is usually more evident once cysts are drained. Thus in these select cases with large lesions that ultimately result in hydrops, in utero surgical removal is likely to be the best form of management.

In the newborn, patients with CCAM may present with severe dyspnea or mild cyanosis or recurrent respiratory infections if the lesion is small. The dyspnea is likely caused by air-trapping by progressive expansion of the cysts. In cases in which the CCAM is small, the lesion may not be well seen with conventional chest radiography and computed tomography may be necessary.

Differential Diagnosis:

The differential diagnosis will depend upon the character of the lesion. Herniation of a dilated stomach or gallbladder into the thorax in a congenital diaphragmatic hernia (CDH) may simulate a Type I or II CCAM. Likewise pleural effusions or a bronchial cyst may simulate a CCAM. Perhaps the most common solid appearing lesion that may simulate a CCAM is a pulmonary sequestration. Two features which may help differentiate these lesions are the systemic supply of pulmonary sequestrations and the small cysts seen in CCAM's. These two lesions may occur together. Larygneal-tracheal atresia may be associated with solid masses within the thorax. The major differentiating feature is their bilateral appearance and dilated fluid filled obstructed bronchi in this lesion. Bilateral CCAMs, though less common, have been reported. Other similarly appearing solid intrathoracic lesions include mediastinal teratoma and rhadomyomas.

References:

Rempen A, Feige A and Wunsch P. Prenatal diagnosis of bilateral cystic adenomatoid malformation of the lung. J Clin Ultrasound 15:3-8, 1987

Saltzman DH, Adzick S and Benacerraf BR. Fetal cystic adenomatoid malformation of the lung: Apparent improvement in utero Obstet Gynecol 71:1000, 1988

Hulnick DH, Naidich DP, McCauley DI, Feiner HD et al. Late presentation of congenital cystic adenomatoid malformation of the lung Radiology 151:569-573, 1984

Maashiach R, Hod M, Friedman S, Schoenfeld A et al. Antenatal ultrasound diagnosis of congenital cystic adenomatoid malformation of the lung: Spontaneous resolution in utero J Clin Ultrasound 21: 453-457, 1993

Joffe GM, Izquierdo LA, Del Valle GO, Key C et al. Congenital lobar adenomatosis, type I The Fetus I:3, 1-8, 1991

Dommergues M, Louis-Sylvestre C, Mandelbrot L, Aubry MC, et al. Congenital Adenomatoid Malformation of the Lung: When is Active Fetal Therapy Indicated? Am J Obstet Gynecol 177:953-958, 1997

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California