It is not pneumothorax: Multicystic lung lesion in a six-year-old child

Abstract

Congenital cystic adenomatoid malformation (CCAM) – recently reported as congenital pulmonary airway malformation – is a rare abnormality of lung development. We present a case of a six-year-old child having a cystic lung lesion that proved to be CCAM after surgical resection. The child is performing well on follow-up.

Introduction

Congenital cystic adenomatoid malformation (CCAM) is a rare developmental anomaly of the lung tissue ¹ which was first described as a distinct entity by Ch’in and Tang in 1949, ² having also been recently referred to as congenital pulmonary airway malformation. ³ It arises from excessive disorganized proliferation of tubular bronchial structures excluding the alveoli which are believed to represent focal pulmonary dysplasia. ⁴ In this anomaly, an entire lobe of the lung is replaced by a non-working cystic mass of abnormal lung tissue whose blood supply is derived from the normal lung circulation. ⁵ Although the cause is unknown, ¹ they are considered to be bronchopulmonary foregut malformations, probably caused by an arrest in lung development between the fourth and seventh week of fetal life. ⁶ CCAM can affect any lobe of the lungs and commonly presents in the neonatal period; up to 90% are diagnosed within the first two years of life. ⁷

Case report

A six-year-old male child presented to the emergency department with respiratory distress and history of chronic cough. The child had a history of recurrent episodes of respiratory infections in the past that were treated with antibiotics and bronchodilators and considered virus-induced wheezing for a prolonged period. None of his family members had a similar condition. On examination, the child was afebrile and of average body build. Respiratory system examination revealed decreased movements on the right side of the chest wall with diminished breath sounds over the right lung base with no adventitial sounds. Other systems examination revealed no abnormality. His birth and postnatal period were free from respiratory symptoms and no other congenital anomalies.

Imaging findings

Initial chest radiography showed radiolucent right hemithorax with mediastinal shift (Figure 1). The initial diagnosis was pneumothorax, but the absence of pleural line or collapsed lung was confusing, so chest computed tomography (CT) was ordered. CT of the chest revealed a hyperinflated right lung with a multicystic mass in the right lower lobe containing multiple air-filled thin-walled cysts varying in size from a few millimeters up to 10 cm (Figure 2). All laboratory data were normal.

Figure 1.

Chest radiograph shows radiolucent right hemithorax.

Figure 2.

Unenhanced chest CT scan shows multiple small, thin-walled cysts with air trapping in the right hemithorax.

Management

The patient was managed conservatively until stabilization of general condition. Surgical management was recommended due to recurrent lower respiratory tract infections and respiratory distress resulting from cyst enlargement; a lobectomy was thus performed.

Pathological evaluation

Gross pathologic findings showed a multilocular cystic lesion that measured 12.5 cm × 9.5 cm × 1 cm with a smooth outer surface. The cut surface had a fine spongy appearance with multiloculated thin-walled cystic spaces of varying sizes ranging from 0.5 to 10 cm. The maximum wall thickness measured 0.5 cm and was filled with frothy red fluid.

Microscopic examination revealed lung tissue showing an area transformed into cystic spaces of variable size; the wall thickness exceeding 100 µm partially lined by columnar epithelium (Figure 3(a)) with occasional papillary excrescences (Figure 3(b)). There were also other larger cysts with wall thickness of less than 100 µm lined by low cubical and flat epithelial cells. These findings were considered diagnostic for CCAM. Subtyping was controversial, with histological features overlapping between Stocker Types 1 (with columnar and papillary lining foci and thick walls) and 4 (with larger, thinner-walled cysts with flat linings).

Figure 3.

(a) Histology slide shows multiple cystic spaces with intervening normal to enlarged airspaces (hematoxylin-eosin stain); (b) Histology slide shows the cysts have an attenuated respiratory epithelial lining (hematoxylin-eosin stain).

The postoperative condition of the patient was uneventful, and he was discharged within 10 days. The patient has been followed-up since then, and at present is doing well without any respiratory symptoms and all clinical parameters are normal. The rest of the right lung was inflated and well developed.

Discussion

Congenital cystic lesions of the lung are rare; the most common malformation of the lower respiratory tract being CCAM. ⁸ We highlight a male child with a cystic lung lesion, presenting with acute respiratory distress due to the expansion of cysts seen as hypertranslucency of the right side, which may be misdiagnosed as pneumothorax. The patient also had a history of recurrent lower respiratory infection that was indicative of CCAM. The presentation of CCAM is variable and may be totally asymptomatic. ⁹ However, the most common mode of presentation is acute respiratory distress with secondary air trapping leading to cyst expansion and compression of surrounding structures. ¹⁰ In most published reports, the CCAM present in childhood ¹¹ usually presents with respiratory distress in neonates, although this may also be manifested in older children and in adults. ¹² Though some studies state that CCAM is more common in males, it has no racial or sexual predilection. CCAM is usually isolated, but in about 10% of cases there are associated anomalies; hence, early detection of this entity is crucial because its prognosis often depends on the severity of the associated anomaly. ¹³ Our patient was thoroughly investigated for other congenital anomalies and was found to be free from them. The CCAM was limited to the lower lobe in our patient. Carias and Orillaza ¹³ found that CCAM is limited to a single lobe in 95% of cases and is bilateral in less than 2% of cases. Solitary lesions usually involve a lower lobe. ¹²

CCAMs were originally categorized into three subtypes by Stocker et al., ¹⁴ with the classification subsequently expanded to include five subtypes (0–4) depending on the proportion of cysts and adenomatous tissue and the dominant cell types. ¹⁵ All types are intrinsically the same lesion, which differ in the radiological presentation. ¹ The newer classification system involving types 0 and 4 has not been widely applied because type 0 is hard to differentiate from bronchogenic cysts and similarities between type 4 and cystic pleuropulmonary blastoma may result in misdiagnosis. ¹⁶

Type 0 CCAM is very rare as it has severe and lethal presentation; it arises from the trachea or bronchus. The cysts are small. ¹⁷ Type 1 CCAM is the most common form, and accounts for 50% to 70% of cases. It arises from the distal bronchus or proximal bronchiole, usually with a small number of large (3 to 10 cm) echolucent cysts. ¹⁷ A single dominant cyst may also be seen. Cyst walls are thin and are lined by ciliated pseudostratified epithelium, with possible papillary excrescences and mucinous-type epithelium. Cartilage may be found in the walls of the cysts. ⁸ Type 2 CCAMs represent 15% to 30% of cases and arise from terminal bronchioles. They are composed of smaller (0.5 to 2 cm) cysts, as well as solid areas that may be difficult to distinguish from surrounding tissue. These are lined by ciliated cuboidal or columnar epithelium, and elements of bronchioles or alveoli may be seen. The incidence of associated anomalies is high (up to 60% involving most organ systems), and prognosis depends on these findings. ¹⁷ Type 3 CCAM accounts for 5% to 10% of cases. This form of CCAM is composed of very small cysts, with the mass appearing to be solid and highly echogenic on ultrasound. These masses may be large and may distort the thoracic contents, with prognosis depending on the degree to which they do so. Type 3 CCAMs are thought to arise from the acinar-like tissue. The tissue is acinar and shows adenomatoid elements consistent with distal airway. ⁸ Type 4 CCAM accounts for 5% to 15% of cases. These CCAMs contain large cysts up to 10 cm and have been associated with malignancy, specifically pleuropulmonary blastoma. They are alveolar in origin. ¹⁸

Following this classification, our patient demonstrated mixed pattern of type 1 and 4 CCAM with predominant type 1 CCAM, being composed of large cysts larger then 3 cm in diameter and lined by bronchial epithelium. These are usually present in the first days of life but may be passed unnoticed until later in life. ¹⁹ Giubergia et al. reported eight cases of mixed types 1 and 2 CCAM and one case of mixed types 1 and 4 CCAM in the same lobe among 172 pediatric cases. ²⁰ This mixed-type CCAM was seen in our patient.

The rarity of this lesion and its commonly associated complications mandates a high index of clinical suspicion for early diagnosis. It is important to consider diagnosis in cases of recurrent respiratory tract infections or pneumothorax. Early diagnosis prevents complications of cyst expansion, air leak or pulmonary hypoplasia. ²¹ CT of the chest is diagnostic but pathological examination is important for definitive diagnosis. Asymptomatic patients can be observed with serial imaging. ²² Lobectomy is the treatment of choice. ¹²

Conclusion

The clinical and radiologic features of cystic lung lesions are variable. Although rare, CCAM should be considered in the differential diagnosis of cystic lung lesions in childhood. CT chest and pathological examinations are required to make a definite diagnosis. Lobectomy is the treatment of choice to avoid complications.