Congenital pulmonary airway malformation

A congenital pulmonary airways malformation (CPAM) is a multi-cysticmulticystic mass of segmental lung tissue with abnormal bronchial proliferation ². CPAMs are considered part of the spectrum of bronchopulmonary foregut malformations and until recently were described as a congenital cystic adenomatoid malformation (CCAM).

Epidemiology

They account for approximately 25~25% of congenital lung lesions. The estimated incidence is approximately 1:1500-4000 live births and there is a male predominance.

Clinical presentation

The diagnosis is usually either made on antenatal ultrasound, or in the neonatal period on investigation of progressive respiratory distress ^3-4. If large, they may cause pulmonary hypoplasia, with resultant poor prognosis. 

In cases where the abnormality is small, the diagnosis may not be made for many years or even until adulthood. When it does become apparent it is usually as a result of recurrent chest infection ^3-4. 

PathophysiologyPathology

The condition results from failure of normal broncho-alveolarbronchoalveolar development with hamartomatous proliferation of terminal respiratory units in a gland-like pattern (adenomatoid) without proper alveolar formation.

Histologically, they are characterised by adenomatoid proliferation of bronchiole-like structures and macro- or microcysts lined by columnar or cuboidal epithelium and absence of cartilage and bronchial glands. 

These lesions have intracystic communications and, unlike bronchogenic cysts, can also have a connection to the tracheobronchial tree.

Sub types

At least four sub typessubtypes are currently classified, mainly according to cyst size.

• type I
  • most common: 70% of cases ³
  • large cysts
  • one or more dominant cysts: 2-10 cm in size
  • may be surrounded by smaller cysts
• type II
  • 15-20% of cases ³
  • cysts are less than 2 cm in diameter
  • associated with other abnormalities
    • renal agenesis or dysgenesis
    • pulmonary sequestration
    • congenital cardiac anomalies
• type III
  • ~10% of cases
  • microcysts: < 5;5 mm in diameter
  • typically involves an entire lobe
  • has a poorer prognosis
• type IV
  • unlined cyst
  • typically affects a single lobe

Location

Lesions are usually unilateral and involve a single lobe. Although there isn't ais no well documented-documented lobar predilection, they appear less frequently in the right middle lobe ³. 

Associations

• hybrid lesion: e.g. CPAM + pulmonary sequestration 
• renal agenesis ⁷

Radiographic features

The appearance of CPAMs will vary depending on the type. 

Antenatal ultrasound 

These lesions appearCPAM appears as an isolated cystic or solid intrathoracic mass. A solid thoracic mass is usually indicative of a type III CPAM and is typically hyperechoic. There can be mass effect where the heart may appear displaced to the opposite side. Hydrops fetalis or polyhydramnios may develop ³ and may be detected on ultrasound as ancillary sonographic features³. Alternatively, the lesion may remain stable in size, or even regress ⁵.

Plain filmConventional radiography

Chest radiographs in type I and II CPAM'sCPAMs may demonstrate a multicystic (air-filled) lesion. Large lesions may cause mass effect with resultant, mediastinal mediastinal shift, and depression, and even inversion of the diaphragm. In the early neonatal period the cysts may be completely or partially fluid filled-filled, in which case the lesion may appear solid or with air fluid-fluid levels. Lesions may change in size on interval imaging (expand from collateral ventilation via pores of Kohn). Type III lesions appear solid.  

CT

CT has a number of roles in the management of CPAMs. FirstlyFirst, it more accurately delineates the location and extent of the lesion. Secondly, and most important in surgical candidates, CT angiography is able to identify systemic arterial supply if present.

Appearances once more reflectAppearance reflects the underlying type where, and a type III lesion can appear as a consolidative areaconsolidation. 

Complications

Potential post natalpostnatal complications include:

• recurrent pneumothorax
• haemopneumothorax
• pyopneumothorax
• possible incidence of certain malignancies, which include including ³:
  • bronchoalveolar carcinoma
  • bronchogenic carcinoma
  • pleuropulmonary blastoma
  • rhabdomyosarcoma

Potenetial in utero complications include

• development of hydrops fetalis may rarely resultdevelop when there is severe compression of the fetal heart or great vessels
• a significant compression of the normal fetal lung can also rarely cause pulmonary hypoplasia

Treatment and prognosis

There can be wide spectrum in prognosis.

Surgery (elective lobectomy) is the treatment of choice in symptomatic patients, both in those presenting early with respiratory compromise and in those presenting later with recurrent infections ³. Type I lesions generally have the best prognosis.

In the setting of a small stable asymptomatic lesion, surgical excision is more controversial. Advocates for excision quote the reported risk of developing malignancies within the lesion (see above). An alternative approach is to watch and wait.  ThereThere are reports of spontaneous regression, particularly in those serially followed up on antenatal ultrasound ^7,10.

Differential diagnosis

General imaging differential considerations include

• bronchogenic cyst 
• pulmonary sequestration (blood supply from arterial system)
• congenital diaphragmatic herniation
• congenital lobar emphysema
• localised congenital cystic bronchiectasis

For type I lesions on CT also consider

• cicatrization collapse with scarring and traction bronchiectasis