The CPAM, previously known as congenital adenomatoid malformation, is the most common congenital lung malformation. It is a lesion characterized by abnormal branching of immature bronchioles that may communicate with the tracheobronchial tree. The CPAM usually has arterial blood supply originating from the normal pulmonary circulation and venous drainage into normal pulmonary veins. However in hybrid lesions, a systemic blood supply may be evidenced. These lesions are often diagnosed on prenatal US or MR imaging (Daltro et al. 2004; Bulas and Egloff 2011). Fetal MR imaging is helpful in its ability to distinguish CPAM from other entities such as CDH, BPS, bronchogenic cyst, neurenteric/enteric cyst, laryngeal or tracheal atresia, and mediastinal cystic teratomas.

For clinical management, the classification into micro- or macrocystic appearance has been used. Adzick el al. (1985) suggested classifying CPAMs into two types: macrocystic (>5 mm) and microcystic (<5 mm). However, the original classification of Stocker et al. (1977) remains more commonly used. These authors divided the lesions into three types: type I, macrocystic (>2 cm); type II, multiple small cysts; and type III, solid form (microscopic cysts). A newer classification proposed by Stocker (2002, 2009) considered also the pathologic analysis to the categorization, with the lesions that have been classified according to cyst size and histologic similarity to segments of the developing bronchial tree and airspaces. Five types were proposed by these authors: type 0 a tracheal or bronchial origin and is pathologically defined as acinar dysgenesis or dysplasia; type 1 is defined as large cystic lesions (2–10 cm) with a bronchial or bronchiolar origin; type 2 represents the small cystic lesions (0.5–2 cm) with a bronchiolar origin; type 3 has a bronchiolar–alveolar duct origin (adenomatoid type) with microscopic cysts; and type 4 with distal acinar origin and usually localized to one lobe and demonstrated large cysts with mediastinal shift. Given the controversial and occasionally confusing terminology and the paucity of literature correlating pathology, it is best to carefully describe the anatomy of the malformation and associated changes related to large lesions to guide any surgery or management (Epelman et al. 2010). Depending on the type of the CPAM, the US and MR imaging may vary. The cystic components will present as an anechoic mass by US and will be bright on T2-weighted MR images (Figs. 2 and 3). On the other hand, solid components of CPAM will present as a homogeneous echogenic mass by US and hyperintense lesions on T2-weighted MR images.

The natural history and prognosis of CPAM are variable. Maximum growth of a CPAM lesion typically occurs between 20 and 26 weeks of gestation. In the late second trimester, the mass often decreases in size (Bulas and Egloff 2011). The prognosis associated with this lesion is dependent on the size, rather than the histologic type of the lesion. Larger lesions are associated with higher frequency of mediastinal shift, pulmonary hypoplasia, vascular compromise, hydrops, and also hydramnios (Hubbard et al. 1999; Witlox et al. 2011; Schrey et al. 2012; Biyyam et al. 2010).

Bronchopulmonary sequestration is a mass of pulmonary tissue that does not communicate with the central airway through a normal bronchial connection, and that receives its blood supply through an anomalous systemic artery, resulting in a nonfunctioning lung tissue. The arterial supply may arise from the descending thoracic or abdominal aorta, or from one of its branches (Daltro et al. 2010). Bronchopulmonary sequestration may be extralobar or intralobar, although most often the BPS present as hybrid lesions with components of both sequestration and CPAM. The hybrid cases are described as a cystic lesion with a feeding systemic vessel (Fig. 4). The extralobar form is most commonly diagnosed in the prenatal and neonatal periods, whereas the intralobar form, although nowadays could be seen in the prenatal period, is more commonly seen in childhood. Some of the BPS lesions may regress in utero (Daltro et al. 2004; Epelman et al. 2010).

Prenatal US demonstrates bronchopulmonary sequestration as a homogeneously hyperechogenic mass in the lower lobes of the lung. On MR imaging, sequestered lung tissue has markedly high signal on T2- and low signal on T1-weighted images. The characterization of the anomalous vessels is possible by US but very difficult by MR imaging (Fig. 5).

The differential diagnosis of pulmonary sequestration may include neuroblastoma and adrenal hemorrhage to the infradiaphragmatic lesions. Pulmonary sequestration is more commonly seen as a solid lesion located on the left side, and can be seen with US during the second trimester. On the other hand, neuroblastoma usually contains cystic areas, which occurs more frequently on the right side and is more commonly diagnosed in the third trimester (Kays et al. 2006; Biyyam et al. 2010).

The bronchogenic cyst is the most common cystic lesion of the mediastinum. It is classified as an anomaly of the ventral bud of the primitive gut that occurs between the 26th and 40th days of embryonic development. The walls of bronchogenic cysts are thin, covered by respiratory epithelium and contain mucinous material. Most of the cysts are seen in the mediastinum or near the carina (Fig. 6). Less commonly, the cysts may occur within the lung parenchyma, pleura, or diaphragm. When the cysts are seen in the lung parenchyma, they are usually located in the inferior lobes. Bronchogenic cysts are sometimes found in association with other congenital pulmonary malformations such as sequestration or lobar overinflation (Daltro et al. 2004; Stocker 2009).

The neurenteric cyst is the main lesion included in the differential diagnosis of bronchogenic cysts. The walls of neurenteric cysts have nervous and gastrointestinal elements, with intestinal epithelium that may be ciliated. They are usually seen in the posterior mediastinum, and may communicate with the esophagus, stomach, or duodenum. Neuroenteric cysts are frequently associated with anomalies of vertebral segmentation, and they can be asymptomatic at birth or present minimal respiratory distress (Fig. 7) (Newman 2006).

Pulmonary arteriovenous malformations (PAVMs) result from an abnormal communication between the pulmonary arteries and veins. Most of the lesions are congenital in origin and the female: male ratio is around 2:1. Infants and children with PAVMs may be asymptomatic; however, if the lesions are large enough to cause a significant right-to-left shunt, the patient may present with cyanosis or heart failure. Between 50 and 70 % of PAVMs occur in the lower lobes and about 2/3 of the patients have multiple lesions (Hansell et al. 2005) (Fig. 8).

Congenital pulmonary lymphangiectasia is a generalized dilation of otherwise histopathologically normal lymphatic vessels. The condition may occur primarily, or secondary to severe pulmonary venous obstruction in cases of total anomalous pulmonary venous return or hypoplastic left heart syndrome. Congenital pulmonary lymphangiectasia is frequently associated with genetic diseases, including Noonan, Turner, Ehlers-Danlos, and Down syndromes (Faul et al. 2000) (Fig. 9).