Introduction

Congenital pulmonary airway malformation is a rare developmental dysplastic lesion of the lung [1] [2]. It is also known as congenital adenomatoid malformation. It has been found that it occurs due to arrested development of the foetal bronchial tree during the 6th and 7th week of foetal development [3] [4].

It is believed that congenital pulmonary airway malformation is a part of the spectrum of bronchopulmonary foregut malformation [5]. About ~25% of a congenital lung lesion is CPAM [6] [7]. It has an incidence of about 1:1500-4000 of total live births [8].

It is usually diagnosed antenatally by routine ultrasound examination. The lesion is usually unilateral and involves a single lobe [9] [10]. It appears as an intra-thoracic cystic or solid-appearing echogenic lesion on ultrasound [11]. Differential diagnosis like broncho-pulmonary sequestration, and congenital diaphragmatic hernia can be excluded by doing B mode & doppler USG [12].

Depending on the size of the cysts we can also detect the type of CPAM [13] [14]. The mortality rate of CPAM is low and has a favourable prognosis: hence with proper care & counselling pregnancy can be continued with postnatal follow-up [15]. Here, we are presenting 4 cases of ante-natally detected CPAM with their sonographic appearance and post-natal follow-up.

Case 01

A 21-year-old female patient, primigravida attended our department at 23 weeks 4 days of gestational age for a routine anomaly scan. The ultrasound examination revealed a small cystic lesion (1.2x 0.9 cm) in the left lung without significant mass effect or vascularity on colour Doppler study.

The lesion was seen above the diaphragm and separated from the fundic bubble. The lesion is classified as type 2 according to Stoker’s classification. Amniotic fluid volume was normal. No other abnormality was noted.

The patient was counselled and the pregnancy was continued. At term, LUCS was performed: baby cried immediately after birth and the birth weight was 2950 grams.

Case 02

28 years female primigravida came to our department at 34 weeks of gestational age for a routine ultrasound. The ultrasound examination showed increased echogenicity in unilateral lung parenchyma with ipsilateral hyperechogenic lung also appearing larger than normal, predominantly in the left hemi thorax. No significant blood supply was seen.

Figure 4: Ante-natal USG showing increased echogenicity of unilateral lung parenchyma

Figure 5: USG also demonstrates the mass effect of the echogenic enlarged lung on the heart which is pushed to the right side

Case 04

32-year-old 2nd gravida attended our department at 19 weeks of gestational age for routine examination. A routine ultrasound revealed a few cystic lesions with more than 2cm lesion in the left lung. No significant mass effect or internal vascularity was seen. Diagnosis of type 1 CPAM was made. On serial follow-up, these cystic lesions gradually became smaller in size.

The baby was born by normal vaginal delivery and cried immediately after birth. The post-natal period was uneventful. Chest X-ray was done after a few months and showed near homogeneous opacity in the left upper region in the paramedical location. As the child did not develop any symptoms of chest infection or respiratory distress, no further investigations were done.

Discussion

Congenital pulmonary airway malformations were first identified in 1949 by Ch’in and Tang as distinct and rare lesions that occurred in stillborn or premature newborns with anasarca. These are the most common congenital lung malformations with an estimated incidence of about 1:1500-4000 live births constituting about ~ 25% of congenital lung lesions.

It is a benign nonhereditary congenital lung lesion which can present as a cystic or solid mass. The pathophysiology of CPAM development is controversial. Some author believes it is due to the arrested development of the localized portion of the bronchial tree during the 6^th and 7^th weeks of foetal development. Others believe these lesions are hamartomata lesions of the bronchial tree. TTF1 play an important role in the development of CPAMS. Disruption of TTF-1 either by mutation or deletion can lead to the development of CPAMs. CPAMs are usually diagnosed antenatally by routine ultrasound and present as cystic [9] or solid-appearing lesions.

Lesions can remain stable in size, enlarge in size or be associated with polyhydramnios or foetal hydrops fetalis, which carries a poor prognosis. On some occasions, they present with respiratory distress or recurrent chest infection. Ultrasound is the imaging modality of choice for diagnosis, and determination of size. Echogenicity, vascularity, and any other associated abnormality.

To our knowledge, CPAM carries a favourable prognosis with a low mortality rate. Many of the lesions gradually reduce in size with no definite symptoms in the post-natal period. Type 1 CPAM is associated with neoplastic transformation. Bronchoalveolar cell carcinoma is the most common form of malignancy associated with CPAM in adults. The vast majority of authors recommend surgical excision of the mass for definite lesions.

Conclusion

Congenital pulmonary airway malformation is a rare disease. Ultrasound is the imaging modality of choice for ante-natal detection of the lesion. USG also plays a major role in characterising the type of lesion along with differentiating it from others. As it carries a favourable prognosis pregnancy can be continued in the absence of other major congenital abnormalities. The post-natal period can be asymptomatic or the child may be presented with recurrent chest infection or respiratory distress, hence further investigation and management depend upon the clinical scenario.

References