Congenital pulmonary airway malformation, previously named congenital cystic adenomatoid malformation (CCAM) consists of an intrapulmonary mass of disorganized pulmonary tissue that may or may not be accompanied by macroscopic cysts (Stocker 2002). When present, the cysts communicate with the airways and their vascular supply comes from pulmonary circulation. However, there are numerous examples of CPAM fed by systemic blood vessels and in these cases it is extremely difficult to differentiate CPAM from pulmonary sequestration, as they correspond to overlapping malformations (Winters et al. 1997). From the radiological viewpoint the differentiation between CPAM with systemic supply and pulmonary sequestration is impossible. These malformations correspond to the same clinical and radiological entity, although they have a different anatomo-pathological expression.

Ch’in and Tang applied the name “congenital cystic adenomatoid malformation” to a congenital cystic pulmonary anomaly for the first time in 1949. The essential discovery is an adenomatoid proliferation of the terminal bronchioles that produces cysts of varying sizes coated with bronchial epithelium. There is considerably controversy over classification and nomenclature. CPAM has recently been recommended as a preferred term to congenital cystic adenomatoid malformation because not all the lesions are cystic and only type III is adenomatoid. In 1977 Stocker et al. divided CCAM into three groups, depending on whether the cysts were larger than 2 cm (type I), smaller than 2 cm (type II), or the malformation was solid without cysts (type III). (Stocker et al. 1977). An expanded classification (types 0–4) has been proposed representing malformations of larger through smaller airways. In an attempt to maintain a similar ordering of the three types published in 1977, type I, II, and III become type 1, 2, and 3 and the “distal acinar” lesion added is type 4, presenting features of a large cyst generally located at the periphery of the lung. Type 0 is characterized by its involvement of all lobes of the lung and its incompatibility with life (Table 1). A number of reports have been suggesting a relationship between CPAM and pleuropulmonary blastoma (PPB) and it is unclear at this time. Anyway, although Stocker feels based in his experience that they are separate lesions, other authors (MacSweeney et al. 2003) consider that both lesions show histologic overlap.

CPAM can be associated with other congenital malformations such as pulmonary sequestration, tracheal bronchus, tracheal atresia, tracheal diverticulum (Restrepo et al. 2004), and bronchogenic cyst. CPAM can also be associated with congenital BA in the same lobe (Cachia and Sobonya 1981) or can involve more than one lobe or be bilateral. In our experience it occurs with more frequency in lower lobes. CPAM can cause severe respiratory distress in the neonatal period. Beyond this time it is usually discovered when it becomes infected or as an incidental radiological finding (Pulpeiro et al. 1987).

The malformation can escape detection on plain films. Although, these days, however, CPAM is increasingly being diagnosed on antenatal (US) examinations, where it is seen as an echogenic mass, which may or may not contain cysts. Antenatal MR imaging may help to evaluate any associated pulmonary hypoplasia and predict the prognosis. The lesions may disappear completely, may remain unchanged or increase in size and be associated with the development of polyhydramnios or fetal nonimmune hydrops fetalis (Fig. 8) (Paterson 2005).

The appearance of CPAM on radiographs and CT depends on the relative presence of cystic and solid components and whether there is superimposed infection. On plain films, type I presents as one or more dominant cysts with adjacent smaller cysts and solid tissue elements. Type II displays smaller, more evenly sized and spaced cysts. Type III, which is very rare, appears as a solid mass. Large masses produce significant mediastinal displacement. Air-fluid levels are often seen, mainly, but not always, associated with infection. On chest CT, CPAM is seen as multiple thin- or thick-walled, air- or fluid-filled cysts of variable size, expanding the affected lung. Air-fluid levels are often present (Rosado-de-Christenson and Stocker 1991). CPAM may mimic cystic pleuropulmonary blastoma. PPB is probably the same tumor that several authors have reported as mesenchymal sarcoma or rhabdomyosarcoma arising in congenital lung cysts (Ueda et al. 1977). It has also been stated that PPB can arise from preexisting cystic lung disease, but is reasonable to assume that the cystic changes are a component of the PPB, itself (Murphy et al. 1992). As the initial manifestation, pneumothorax is more frequently seen in PPB than in CPAM (Fig. 9) (Senac et al. 1991). However, pneumothorax can be found associated with both entities and the available information does not support the use of this finding as a differentiating diagnostic criteria (Lejeune et al. 1999).

Cases of CPAM/pulmonary sequestration that dramatically decreased in size or disappear completely during pregnancy and infancy have been reported (Fig. 10). However, the clinical management of an asymptomatic child with a congenital mass of the lung remains controversial. Some authors advocate close clinical observation and radiological surveillance (MacGillivray et al. 1993), whereas others, considering the possibility that cystic pulmonary lesions may be infected (Garcia-Peña et al. 2013), or may be harbor or develop PPB, favor elective surgical resection (Samuel and Burge 1999).

Pulmonary sequestration consists of a mass of pulmonary tissue disconnected from the bronchial tree that receives its blood supply from the systemic circulation (Heitzman 1984). Pulmonary sequestration is divided into two groups: intralobar sequestration, in which the tissue is surrounded by normal lung and found in the interior of the visceral pleura, and extralobar sequestration, in which the tissue is disconnected from the bronchial tree and has its own pleural coating. In 1946 Pryce identified intralobar sequestration as a clinical-pathological entity. He was the first to apply the term “sequestration” and further classified the lesion as intralobar or extralobar on the basis of the morphologic patterns of the malformation. There are also mixed cases with characteristics of both intralobar and extralobar sequestration.

Pulmonary sequestration is an uncommon anomaly; the intralobar form is more frequent than the extralobar. Intralobar sequestration constitutes 75 % of all pulmonary sequestrations and is located in the left lower lobe in 60 % of the cases. Only 2 % occur in the upper lobes and 0.25 % in the middle lobe. The affected lung can maintain the normal lung architecture, behave like a mass, or present as internal cysts. Vascularization in the majority of cases is through the thoracic aorta (Savic et al. 1979), or less commonly, through systemic vessels originating from the abdominal aorta or one of its branches (Pedersen et al. 1988). The systemic supply can be formed by multiple, small-caliber blood vessels or by a single vessel, which are histologically similar to the pulmonary artery. This favors the early appearance of atherosclerosis (Ikezoe et al. 1990). Intralobar sequestration does not receive blood from the pulmonary arteries and it drains through pulmonary veins. In exceptional cases it communicates with the digestive tract (bronchopulmonary foregut malformation) (Hruban et al. 1989). It can be bilateral, or associated with other congenital malformations.

Since Pryce’s description of pulmonary sequestration, there has been considerable controversy about its origin. Some authors contend that intralobar sequestration is, in fact, acquired (Gebauer and Mason 1959; Holder and Langston 1986), resulting from endobronchial obstruction leading to chronic pulmonary infection and hypertrophy of the systemic arteries in and around the area of the pulmonary ligament. This explains why, in the past, when infections were poorly controlled, intralobar sequestration was overdiagnosed. However, congenital intralobar sequestration does occur, since this anomaly has been recognized on prenatal US and has been detected in newborns (West et al. 1989; Laurin and Hägertrand 1999) (Fig. 11).

Intralobar sequestration is usually discovered because the patient has developed a pulmonary infection, although some patients are asymptomatic when the lesion is found. In a small number of cases intralobar sequestration debuts as a pulmonary hemorrhage (Fig. 12), pleural effusion (Kim et al. 1997; Lucaya et al. 1984), or pleural bleeding secondary to infarction of the sequestrated lung (Zumbro et al. 1974). On plain films, intralobar sequestration appears as a homogenous opacity mostly in the lower lobes. This opacity can simulate a mass with a well-defined border, or show internal air–fluid levels and a poorly defined border. In rare cases calcifications are present within the sequestration or in the systemic blood vessel. An unusual presentation of intralobar sequestration is localized emphysema without an associated opacity or mass (Ko et al. 2000).

Extralobar sequestration is usually located between the lower lobe and the diaphragm, more frequently at the left thoracic base, in 77 % of cases (Savic et al. 1979). To a much lesser degree it has also been found in the mediastinum, pericardium (Stocker and Kagan-Hallet 1979), diaphragm, or retroperitoneum (Baker et al. 1982). Vascular supply occurs through a systemic artery and venous drainage through the azygos or portal system (Rees 1981), although nearly 25 % are completely or partially drained by pulmonary veins. Extralobar sequestration is associated with other congenital malformations in 65 % of cases, such as diaphragmatic hernia, bronchogenic cyst, BA, scimitar syndrome, pericardial defect and as previously stated, CCAM (Savic et al. 1979), and these are much more frequent than those associated with the intralobar form. Both types of sequestration occasionally can connect with the digestive tract (bronchopulmonary foregut malformation) (Hruban et al. 1989). The presence of air bronchograms within a mass thought to be ELS should suggest the diagnosis of bronchopulmonary foregut malformation. Communication between the tracheobronchial tree and the GI should be examined by upper GI series or MDCT. Extralobar sequestration is usually detected fortuitously and can also be associated with pleural effusion. It may be seen as a homogeneous mass or a small bump on the posterior hemidiaphragm that may be subtle and occasionally inapparent on the chest radiograph.

Ultrasound, CT, and MRI are useful in the study of sequestrations (Fig. 13). Multidetector CT angiography is considered the imaging technique of choice for preoperative evaluation of pulmonary sequestration. MDCT with supplementary multiplanar and 3D images has the advantage of being able to show the pulmonary parenchyma abnormality, as well as the arterial and venous angioarchitecture of the sequestration (Lee et al. 2004, 2011a). CT has some advantages over MR angiography for evaluating pulmonary sequestrations in children. CT scan times are significantly shorter, and resolution of small vessels and lung parenchyma is better. CT in a single phase of contrast injection is adequate for evaluation of both the arterial and the venous anatomy, using low dose to minimize radiation (Abbey et al. 2009; Lee et al. 2011b). Intralobar sequestration typically manifests as a homogeneous or inhomogeneous solid mass, with or without definable cystic changes. It can also appear as an aggregate of multiple small cystic lesions with air or fluid content (Fig. 14), a well-defined cystic mass, or a large cavitary lesion with air–fluid level. The lesion may enhance with contrast material (Frazier et al. 1997; Rosado-De-Christenson et al. 1993). An appearance simulating emphysema, possibly resulting from collateral ventilation and air-trapping, can sometimes be seen in sequestration. Expiratory CT scans are helpful for delineating the extent of the malformation (Fig. 15) (Stern et al. 2000; Lucaya et al. 2000). Extralobar sequestration is seen on chest CT as a homogeneous, well-delimited mass, sometimes with internal cystic areas (Rosado-De-Christenson et al. 1993).

MR imaging is a safe and noninvasive imaging method, which may be useful in some specific cases of pulmonary sequestration (Naidich et al. 1988; Yu et al. 2010). In MR, this anomaly is seen as a well-defined, irregular, or branch-like mass. MR can also reveal the presence of cystic areas, as well as the variable solid, fluid, hemorrhagic, and mucus-containing components. However, MR imaging cannot delineate focal thin-walled cysts or the emphysematous changes of sequestration as clearly as CT. The size, origin, and course of the aberrant systemic artery and the venous drainage can be demonstrated by MR imaging. Breath-hold (if possible) or nonbreath-hold three-dimensional contrast-enhanced MR angiography offer excellent display of the aberrant vessel without flow artifacts (Ko et al. 2000). The advantage of MRI over CT is the absence of radiation. However, long scan times, sedation requirements, and suboptimal evaluation of lung parenchyma are the disadvantages of this method.