A termination of pregnancy was performed and a stillborn male fetus weighing 950g and 36 cm long was delivered. Apart from the distended fetal abdomen, no other external malformations were noticed.
On pathology examination, a huge mass of liver-like appearance was found inside the thoracic cavity. Fetal lungs were reduced to a small part of hypoplastic lung tissue in the upper portion of the right hemithorax. The heart was markedly displaced to the right, closely apposed to the thoracic wall, but was otherwise normal. The diaphragm was present and intact, as well as the abdominal organs, but pushed caudally by the space-occupying lesion in the thorax.
According to the histopathologic examination, the tumor"s tissue was composed of rare bronchiole-like structures and huge masses of cuboidal epithelium surrounding small, irregular areas. Differentiation of epithelial and mesenchymal structures was minimal. Following the classification of cystic adenomatoid malformation proposed by Stocker et al1, the diagnosis of congenital cystic adenomatoid malformation of the lung, type III was confirmed.
Discussion
Prevalence
Cystic adenomatoid malformation is a rare malformation with no preference for location or sex. About 200 cases have been reported in the literature to date2. It is usually unilateral, but a few cases of bilateral involvement have already been reported3.
Pathology
The tumor appears as a mass of variable size that deforms the lung. It is a hamartoma of the lung resulting from cessation of bronchiolar maturation with overgrowth of mesenchymal elements4.
According to Stocker et al, cystic adenomatoid malformation can be classified into three subtypes based upon clinical, gross pathologic and histologic features1,5: Type I has large cysts and contains relatively well differentiated bronchial components. Type II has multiple small cysts of less than 1 cm in diameter, which histologically resemble dilated terminal bronchioles. Associated anomalies are frequently presented in this type of cystic adenomatoid malformation. Type III is a non-cystic lesion, and it typically creates a large solid mass affecting an entire lobe or lobes. Histologically, some small cystic areas measuring 2-5 mm resembling bronchiole can be seen. This type of lesion is less common but almost invariably fatal.
Pathology
Cystic adenomatoid malformation probably results from arrested cellular development in the early gestation1,5. Arterial and venous connections are typically normal. Polypoid proliferation without alveolar differentiation and absence of bronchial cartilage are characteristic features of this lesion. Very often, the tumor is large enough to cause a shift of the mediastinal structures and to compress the remnants of the lungs.
Diagnosis
Cystic adenomatoid malformation has been identified prenatally as early as 18 weeks of gestation6. The diagnosis of the disease relies on the visualization of a nonpulsatile intrathoracic lung tumor that can be solid (Type III) or cystic (Type I, II). Most reported cases describe type I cystic adenomatoid malformation which produces multiple large cysts and an easily recognizable mass without discernible individual cysts. A significant shift in the mediastinum usually occurs and is detected by the displacement of fetal heart. Polyhydramnios and/or hydrops are frequently present, in most cases associated with type III lesion7.
Associated anomalies
Associated anomalies are frequently present in type II cystic adenomatoid malformation, and may dominate the clinical picture postnatally. Apart from polyhydramnios, mediastinal shift and hydrops, associated anomalies include other malformations of the pulmonary system, renal anomalies (like renal agenesis or dysplasia) and gastrointestinal abnormalities (like congenital diaphragmatic hernia, bowel atresia)1,5 heart anomalies (tetralogy Fallot, truncus arteriosus) and skeletal malformations (sirenomelia, deformity of clavicle and spine) have also been reported1,8. Polyhydramnios is frequently present in the antenatally detected cases5. In the absence of fetal hydrops, it is probably related to esophageal compression. Pulmonary hypoplasia is a result of compression on the normal lung parenchyma.
Differential diagnosis
Differential diagnosis includes other intrathoracic lesions. Type I and II cystic adenomatoid malformation should be distinguished from a bronchogenic cyst which is usually small, solitary and near the midline. The echogenic mass in type III cystic adenomatoid malformation may resemble pulmonary sequestration or intrathoracic bowel. Pulmonary sequestration is not likely to cause polyhydramnios or hydrops and has a pyramidal shape. Peristalsis of the bowel in the thoracic cavity is helpful in distinguishing diaphragmatic hernia. Mediastinal tumors can also be suspected, but their incidence is extremely rare.
Prognosis
The prognosis for in utero detected cases depends on the variety of cystic adenomatoid malformation and presence of pulmonary hypoplasia and associated anomalies. In the absence of pulmonary hypoplasia and associated anomalies, the prognosis for a type I cystic adenomatoid malformation is excellent after surgical treatment9. In type II lesion, poor survival rate is usually due to the associated structural or chromosomal anomalies. The worst prognosis is seen in type III lesions, based upon fetal hydrops and/or pulmonary hypoplasia. However, in cases without hydrops, survival after surgical resection is reported10.
References
1. Stocker JT, Madewell JE, Drake RM: Congenital cystic adenomatoid malformation of the lung. Classification and morphologic spectrum. Hum Pathol 8:155-171,1977.
2. Romero R, Pilu G, Jeanty P, et al: Prenatal diagnosis of congenital anomalies. Norwalk: Appleton & Lange,1988.
3. Oestoer AG Forture DW: Congenital cystic adenomatoid malformation of the lung. Am J Clin Pathol 70:595,1978.
4. Nyberg DA, Mahony BS, Pretorius DH: Diagnostic ultrasound of fetal anomalies. Text and atlas. Year book Medical Publishers Inc, Chicago,1990.
5. Miller RK, Sieber WK, Yunis EJ: congenital cystic adenomatoid malformation of the lung: a report of 17 cases and review of the literature. Pathol Annu I, 387-407,1980.
6. Marcos SF, Lobb MO: The antenatal diagnosis by ultrasonography of type III congenital adenomatoid malformation of teh lung. Br J Obstet Gynecol 93:1002,1986.
7. Adzick NS, Harrison MR, Glick PL, et al: Fetal cystic adenomatiod malformation. Prenatal diagnosis and natural history. J Pediatr Surg 20:483-488,1985.
8. Mayden K, Tortora M, Chervenak FA, et al: The antenatal sonographic detection of lung masses. Am J Obstet Gynecol 148:349,1984.
9. Frenckner B, Freyschuss U: Pulmonary function after lobectomy for congenital lobar emphysema and congenital cystic adenomatoid malformation: A follow up study. Scand J Thorac Cardiovasc Surg 16:293,1982.
10. Vergnes P, et al: Malformations pulmonaires de diagnostic antenatal. Chir Pediatr 30:185,1989.