A 38-year-old man with lung cysts.

A 38-year-old man gave history of cough with expectoration and dyspnea since childhood. He had 2-3 exacerbations a year. He denied history of wheezing or hemoptysis. He had no history of exanthematous fever or pneumonia in childhood. There was no relevant occupational history or systemic complaint. He was an ex-smoker, having quit smoking 10 years ago; he had a smoking index of 7.5 pack years. He was married, with three children. His maternal aunt was diagnosed to have bronchial asthma. The physical examination was normal.

The chest radiograph and high-resolution computed tomography (HRCT) of thorax are shown in Figures 1 and Figures 2a and b, respectively. Hemogram and biochemical investigations were normal. Spirometry showed forced vital capacity (FVC): 2.23 L (55% of predicted), forced expiratory volume in one second (FEV1): 1.94 L (56% of predicted), and FEV1/FVC: 87%; there was improvement in FEV1of 200 mL following inhalation of 200 μg of salbutamol.

Figure 1

Chest radiograph (posteroanterior view)

Figure 2a

High-resolution computed tomography of thorax (transverse section)

Figure 2b

High-resolution computed tomography of thorax (sagittal section)

Questions

What do the chest radiograph and HRCT show?

What are the possible differential diagnoses on HRCT thorax? What is the most likely diagnosis if the history and HRCT thorax are correlated?

Which one of the two is the correct terminology: ‘congenital pulmonary airway malformation’ or ‘congenital cystic adenoid malformation’? What is the new classification of this condition?

Answers

The chest radiograph shows multiple ill-defined air lucent opacities in the left upper lobe. On HRCT of the thorax, however, the air lucent opacities appear to be due to multiple confluent cysts of 2-5 cm size each.

The various causes of cystic lesions on imaging are given in Table 1.[1-3] Amongst the congenital malformations, congenital lobar emphysema (CLE) is unlikely because it usually presents before 6 months of age. Also, in CLE, HRCT thorax will show hyperinflated lungs. Bronchogenic cysts are usually single and are seen in the middle third of the lung. The possibility of intralobar sequestration can be considered as the lesions are cystic; however, sequestration is usually seen in the medial aspect of a posterior lung base and hence is unlikely in this case. Congenital pulmonary airway malformation (CPAM) appears to be the most plausible amongst the congenital etiologies. Acquired causes like infection and cysts with interstitial lung disease are unlikely because the cysts are thin walled and the remaining lung parenchyma is normal. The cysts are too large and are located in the upper lobe and hence bronchiectasis is also improbable. A cystic neoplasm is the other possible differential diagnosis. Thus, amongst the congenital malformations and acquired causes of cysts, CPAM and cystic neoplasm are the most likely diagnoses.The patient was subjected to left upper lobectomy. The resected specimen confirmed the presence of multiple large intercommunicating cysts filled with gelatinous mucoid material [Figure 3]. The histopathology showed the cysts to be lined by pseudostratified ciliated columnar epithelium [Figure 4], with underlying fibromuscular bands; the appearance was suggestive of type 1 CPAM.

Table 1

Causes of cystic lung

Figure 3

Specimen of resected lung showing multiple intercommunicating cysts

Figure 4

High-resolution photomicrograph of resected lung

CPAM was earlier known as congenital cystic adenomatoid malformation.[4] Recently, it has been renamed as CPAM because not all the lesions are cystic or adenomatoid.[5] On the basis of the apparent site of origin, five types [Figure 5] have been described in the new classification[6] [Table 2]: Type 0 - alveolar dysplasia or dysgenesis involving the proximal tracheobronchial tree; type 1 - proximal acinus (bronchial/bronchiolar); type 2 -midacinus (bronchiolar); type 3 - bronchiolar/alveolar duct; and type 4 - alveolar saccular/distal acinar.

Figure 5

Types of congenital pulmonary airway malformation

Table 2

Types of congenital pulmonary airway malformation

Discussion

CPAM is a rare hamartomatous developmental anomaly that results from unsystematic spread of tubular bronchioles and enlarged alveolar tissue.[5] It was first described by Chin and Tang in 1949. It is seen in about 1 in 25000-35000 live births.[4] CPAM type 0 is incompatible with life and hence always presents before or immediately after birth. The other types are diagnosed during the neonatal period, when respiratory distress can be caused by inflation of the cysts with spontaneous respiration, or during childhood or adulthood, when the condition causes repeated respiratory tract infection, pneumothoraces, or hemoptysis.[7] CPAM type 1 may sometimes remain asymptomatic.[7] There is no sex predilection or chromosomal anomaly observed with CPAM. Radiologically, type 1 and type 4 have large cysts that may be up to 10 cm in size and type 2 and type 3 have small cysts that are <2 cm in size.[89] Histopathology is essential to confirm the diagnosis and ascertain the type of CPAM.

CPAM may be associated with congenital anomalies such as congenital heart disease (e.g., left heart hypoplasia); pulmonary malformations (e.g., sequestration, pulmonary hypoplasia); skeletal anomalies (e.g., pectus excavatum, genu varum, scoliosis); and renal anomalies (e.g., renal agenesis).[10] Some of these anomalies are common with specific types of CPAM [Table 2]. If CPAM is diagnosed during the early neonatal period, conservative management is recommended, as postnatal regression of the lesion may occur. Surgical intervention remains the gold standard for CPAM diagnosed at later ages because remissions are infrequent and because of the risk of repeated infections and malignant transformation.[11]