Congenital pulmonary airway malformation
Updates to Article Attributes
A congenital pulmonary airways malformation (CPAM) is a multi-cystic 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% 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.
Pathophysiology
The condition results from failure of normal broncho-alveolar 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 types 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
-
type III
- ~10% of cases
- microcysts: < 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 a well 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 appear 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 features. Alternatively the lesion may remain stable in size, or even regress 5.
Plain film
Chest radiographs in type I and II CPAM's may demonstrate a multicystic (air-filled) lesion. Large lesions may cause mass effect with resultant, mediastinal shift, and depression and even inversion of the diaphragm. In the early neonatal period the cysts may be completely or partially fluid filled, in which case the lesion may appear solid or with air 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. Firstly 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 reflect the underlying type where a type III lesion can appear as a consolidative area.
Complications
Potential post natal complications include
- recurrent pneumothorax
- haemopneumothorax
- pyopneumothorax
- possible incidence of certain malignancies, which include including 3:
Potenetial in utero complications include
- development of hydrops fetalis may rarely result 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. There 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
- 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
-<li><a href="/articles/bronchogenic-carcinoma">bronchogenic carcinoma</a></li>- +<li><a href="/articles/lung-cancer-3">bronchogenic carcinoma</a></li>
-<li><a href="/articles/congenital_diaphragmatic_hernia">congenital diaphragmatic herniation</a></li>-<li><a href="/articles/congenital-lobar-emphysema">congenital lobar emphysema</a></li>- +<li><a href="/articles/congenital-diaphragmatic-hernia-1">congenital diaphragmatic herniation</a></li>
- +<li><a href="/articles/congenital-lobar-overinflation">congenital lobar emphysema</a></li>
Image 1 X-ray ( create )
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