Address correspondence to Asim Kurjak, MD, PhD, Ultrasonic Institute University of Zagreb, "Sv. Duh" Hospital, Sv. Duh 64, 41000 Zagreb, Croatia. Ph: 38-41-579-251 Fax: 38-41-579-248.

Synonyms: Cystic adenomatoid malformation of the lung, adenomatoid hamartoma, pulmonary adenoma.

Definition: Hamartoma of the lung.

Prevalence: About 20 reported cases of type III reported to date.

Etiology: Arrested cellular development at an early stage.

Pathogenesis: Cessation of bronchiolar maturation with overgrowth of mesenchymal elements.

Associated anomalies: Polyhydramnios, hydrops, mediastinal shift, anomalies of the pulmonary system, renal, gastrointestinal, skeletal and cardiac anomalies.

Prognosis: Depending on the type of lesion.

Recurrence risk: Not increased.

Management: Pregnancy termination before viability, conservative management after.

MESH Cystic adenomatoid malformation of lung BDE 2501 ICD9 748.4 CDC 748.413^* (also 748.580)

Introduction

Disordered development of fetal lungs frequently results in postnatal respiratory distress or neonatal death. Intrathoracic space-occupying lesions profoundly affect the prenatal development of the lungs. Although congenital cystic malformation of the lung is rare, it can be suspected on ultrasound examination. We present a case of prenatally suspected type III lesion (according to Stocker"s classification) of cystic adenomatoid malformation with bilateral involvement of fetal lungs.

Case report

A 24-year-old white woman, G₂P₂, with one healthy, female child was referred for ultrasound examination. Her pregnancy was uncomplicated, apart from periodic weakness and anemia throughout the pregnancy. A single fetus was observed at 26 weeks (BPD and femur length measurements).

Almost the whole thoracic cavity was filled with a solid, echogenic mass (fig, 1).

The heart was shifted to the right side, closely apposed to the thoracic cavity wall (fig. 2). The mass was extending towards the abdomen, pushing the diaphragm caudally (fig. 2). Inside the mass, blood-flow velocity waveform analysis revealed arterial flow with a resistance index of 0.77. Polyhydramnios was also present. A cordocentesis was performed for genetic evaluation, which demonstrated a normal male karyotype. A poor prognosis was presumed due to the lung hypoplasia.

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 features^1,5: 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 gestation^1,5. 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 reported^1,8. 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.