CDH is a congenital anomaly that affects the development of the diaphragm and allows for intra-abdominal organs to move into the thoracic cavity. It results in lung hypoplasia from lung compression and mechanical complications from mediastinal and cardiac deviation.

CDH can be classified based on location: posterolateral Bochdalek hernia (70–75 %), anterior Morgagni hernia (23–28 %), and central defects (2–7 %) [10]. Most CDHs occur on the left side (85–90 %), some on the right (10–15 %), and only rarely bilaterally (2 %) [11].

CDH can also be differentiated as isolated or complex. CDH is often isolated. However, in 23–43 % of cases, an associated anomaly can be present [12], most likely a cardiac defect (20 %) [11, 13, 14]. When multiple abnormalities are present, genetic anomalies should be considered with a higher mortality [14]. More than 50 genetic causes have been described and can vary from chromosomal abnormalities such as trisomy 18, microdeletions, or microduplications to syndromes with unknown genetic mutations (Fryns syndrome).

US findings seen in patients with CDH include presence of stomach bubble, gallbladder or bowel within the thoracic cavity, deviation of the heart and mediastinum, herniated liver, abnormal position of the umbilical and hepatic veins, pleural effusion, and polyhydramnios [11, 13, 15]. MRI is an adjuvant study helping to confirm the diagnosis, aiding in the search for additional abnormalities, and providing additional data such as lung volumes that may help predict outcome.

MRI better demonstrates the position of the liver and the amount of herniation due to superior differentiation of the hepatic lobe (bright on T1) from the compressed lung or a solid type of CPAM [16–18]. MRI can also help by providing better evaluation of the bowel with bright T1 signal of meconium and allowing visualization of the normal ipsilateral and contralateral lung [19] which is useful in the assessment of pulmonary hypoplasia [7] (Fig. 9.3). Suggestion of a hernia sac by a rounded appearance of the most superior aspect of the hernia has been associated with a better prognosis [7, 16] (Fig. 9.4).

Different volumetric measurements can be obtained with MRI and used as indicators of outcome. MR measurements allow assessment of both lungs and can be more reliably obtained than US [17]. MRI measurements include total lung volume, observed to expected total lung volume (o/e TLV), percent predicted lung volume (PPLV), fetal lung volume to fetal body volume ratio (FLV/FBV), percent liver herniation (%LH), and herniated liver to fetal thoracic volume ratio (LiTR).

MRI can measure the diameter of the aorta and pulmonary arteries used to obtain the modified McGoon index as a prognostic indicator of pulmonary hypertension [19].

Imaging with diffusion-weighted sequences to assess growth and maturity has been attempted though no correlation has been seen with lung volume or fetal survival [20].

Prognosis varies depending on the side of the herniation, the position of the liver, associated abnormalities, and age at diagnosis [12].

The presence of herniated liver decreases survival from 74 to 45 % [21], and the presence of associated anomalies also decreases the survival [12]. The severity of lung hypoplasia and resulting lung hypertension are major determinants in the mortality and morbidity of the patients [22–24], and a larger herniation diagnosed earlier results in worse pulmonary hypoplasia with a resulting higher mortality.

Bilateral hernias are usually fatal. Familial and syndromic hernias usually have a worse prognosis compared to isolated hernias [25].

Different ultrasound and MRI measurements have been used to estimate the severity of lung hypoplasia and probable outcome of the fetus:

In a study by Ruano et al., the best combination of measurements to assess mortality is o/e TLV and %LH [24].

Ultrasound methods exist to predict pulmonary hypertension. By MRI, the modified McGoon index can be obtained by adding the right pulmonary artery diameter plus left pulmonary artery diameter and dividing the sum by the diameter of the descending aorta measured at the level of the diaphragm [19].

Complete anatomical examination should be performed to assess for presence of associated anomalies (25–75 %) [35]. Echocardiography is indicated as congenital cardiac defects occur in 10–35 % of cases and decrease survival from 73 to 67 % if it is a minor defect or 36 % if major complex cardiac defect [25].

A prenatal karyotype with microarray is indicated to assess for chromosomal anomalies, present in 10–20 % of cases [14, 35].

Follow-up ultrasound examinations should be performed to assess fetal well-being, lung volume, and changes in mediastinal shift that could result in hemodynamic changes [36]. Third trimester follow-up MRI can be performed to assess lung volume near time of maximal intrauterine growth and plan delivery; this late MRI can also be used for postnatal surgical planning decreasing the need for postnatal cross-sectional imaging [19].

Different fetal surgical techniques have been attempted, such as in utero repair and fetal tracheal occlusion via open surgery or endoscopy, with clip or balloon occlusion. EXIT to ECMO is also offered in some centers but has not demonstrated significant survival benefits [21]. New nonsurgical prenatal options are being evaluated, including pharmacologic treatments and stem-cell-based strategies, and could be promising in treating pulmonary hypertension and hypoplasia [23].

CPAM is a congenital anomaly of the lung resulting in a cystic, hamartomatous mass of lung tissue that communicates with the bronchial tree through an abnormal communication and has normal pulmonary blood supply and venous drainage into the normal pulmonary veins [37].

CPAM has been classically classified based on pathology by Stocker et al. into type I (large cysts, more than 2 cm), type II (multiple small cysts), and type III (microcystic). Adler et al. described a simplified classification based on gross appearance, and its use is recommended in fetal medicine:

It usually affects one lung (95 %) but can be seen bilaterally, and both lungs can be affected. It is usually unilobar (85–95 %) and usually occurs in the lower lobes [38].

MRI findings are characteristic of fluid-filled structures, demonstrating bright T2 signal. A solid appearing lesion or a multicystic mass lesion with small or large cysts surrounded by abnormal hyperintense parenchyma is appreciated in the thoracic cavity, depending on the type of CPAM (Fig. 9.5). The lesion exerts mass effect on the heart and other mediastinal structures causing heart rotation and shift to the contralateral side with different degrees of compression of venous structures and results in impaired venous return (Fig. 9.6). As a complication from mass effect and compression, pleural effusion, pericardial effusion, skin thickening, and/or ascites can develop (Fig. 9.7). Dilatation of the proximal esophagus can also be seen due to esophageal compression. As the fetus grows, the lesion becomes less conspicuous by ultrasound and can be better seen by MRI [3].

MRI allows evaluation of the residual normal lung and can sometimes be beneficial differentiating CPAM from other lung anomalies and identifying associated congenital anomalies [4, 39–41]. It can also help in differentiating between complete resolution and the presence of residual lesions, important for postnatal follow-up planning [7].

Prognostic indicators include the size of the lesion, amount of mediastinal shift, and presence of polyhydramnios and/ or hydrops. Macrocystic lesions usually have a favorable prognosis, since most cases have a slow growth. When large, either macro- or microcystic, lesions can cause mediastinal shift and result in hemodynamical changes including polyhydramnios and nonimmune hydrops, which may require in utero intervention.

The CPAM volume ratio (CVR) [42], a measurement described by ultrasound, should be measured to assess prognosis and risk of hydrops. It is obtained by calculating the volume of the lung mass (height × anteroposterior diameter × transverse diameter × 0.52) and dividing it by the head circumference. A CVR <1.6 indicates a 14 % risk of developing hydrops for macrocystic lesions and 3 % for microcystic lesions. If CVR is >1.6, the risk increased to 75 % [42] (Fig. 9.8).

CPAM typically demonstrates an increase in size between 20 and 26 weeks of gestation and then plateaus [43]. It can later decrease in size [43] or seem to disappear due to similar signal intensity compared to normal lung parenchyma [44]. A residual mass can be seen in postnatal images in 40 % of cases when resolution by prenatal images was suspected.

Differential diagnosis includes BPS, CLO, bronchogenic cyst, CDH, laryngeal or tracheal occlusion, neurenteric/enteric cysts, and mediastinal teratomas.

Associated abnormalities and chromosomal abnormalities are seen in 8–20 % of patients, so a thorough examination should be performed [7, 45, 46].

BPS is a congenital anomaly of the lung characterized by a mass of nonfunctional lung tissue, usually affecting the lower lobes, without communication with the bronchial tree. Arterial supply to the mass is systemic and usually originates from the aorta, either lower thoracic or upper abdominal aorta. Other origins such as from the gastric artery and splenic artery can also occur [47].

BPS can be classified based on anatomical characteristics either intralobar (75 %) or extralobar (25 %) [48]. An intralobar lesion shares the visceral pleura of the rest of the normal lung, and venous blood drains into the pulmonary venous system; extralobar sequestration has its own visceral pleura, drains into the systemic veins, and is most commonly diagnosed in the prenatal or perinatal period [37, 48].

Based on location, the majority of BPS are supradiaphragmatic (85 %), and the remaining cases are either diaphragmatic or infradiaphragmatic (10 %) [37, 49]. Description of the location is important in order to provide a better differential diagnosis and follow-up evaluation; subdiaphragmatic lesions must be differentiated from neuroblastomas and adrenal hemorrhage [37, 48].

When a BPS coexists with a CPAM, it is called a hybrid lesion, and they can have both systemic and pulmonary arterial feeders (Fig. 9.9). 25–50 % of extralobar sequestrations are hybrid lesions [36].

MRI demonstrates a well-defined, wedged-shaped lung mass that is hyperintense on T2-weighted sequences. A low-signal linear structure representing the lung mass feeder can sometimes be seen by MRI but is usually better seen by ultrasound, by power and color Doppler (Fig. 9.10). MRI is beneficial in the delineation and better localization of the mass. MRI also allows for better evaluation of the contralateral lung and in the assessment of associated congenital anomalies.

Follow-up MRI may demonstrate a smaller lesion with hypointense T2 signal compared to the lung if the lesion either decompressed into the lung, outgrew the systemic circulation, or had a vascular/lymphatic obstruction due to torsion [50].

Prognosis depends on the size of the lesion and presence of hydrops. When the mass is large, it can cause mass effect on the mediastinal structures. If significant compression is exerted on the heart and venous structures, hydrops can occur; if the esophagus is compressed, polyhydramnios can be seen [41, 50, 51]. Most have a good prognosis since the majority decreases in size in utero (75 %), and hydrops is rarely seen [4, 41, 48, 50]. If hydrops develops as a complication, the survival decreases to 20–30 % [50].

Serial follow-up examinations should be performed. The majority (75 %) of prenatally diagnosed BPS decreases in size and becomes harder to see by ultrasound, but an increase in size can also be seen. Follow-up examinations are performed with ultrasound for reevaluation of the lesion, change in size, variation in mediastinal compression, and presence of hydrops. Closer follow-up is recommended for larger lesions given with higher risk for hydrops. Late MRI can be performed to better delineate the feeding vessels, with a better correlation with postnatal imaging [52]. In some institutions, postnatal imaging is not performed if prenatal MRI properly depicts the feeding vessel for surgical planning.

Thorough examination of the entire fetus should be performed looking for associated congenital anomalies, especially in the presence of a suspected extralobar type. Fetal karyotype should be recommended if fetal intervention could be considered in the future management.

Fetal intervention is indicated in the presence of hydrops earlier in pregnancy and significantly increases survival [51, 53]. If hydrops develops after weeks 32–34, early delivery and postnatal management is an option [41].

Different fetal interventional techniques have been performed, including thoracentesis as a temporizing option, thoracoamniotic shunt, percutaneous laser ablation, and in utero open resection; for delivery, ex utero intrapartum therapy can be offered if needed [41, 53–62].

CLO is a rare entity characterized by overinflation of the lung. It is usually unilateral and usually affects one lobe; involvement of more pulmonary lobes [63] and bilateral lesions has been described.

In neonates who present with respiratory distress, the left upper lobe is most commonly affected followed by right middle and right upper lobes; in prenatal cases, a predisposition for lower lobe involvement and a high association with bronchial atresia have been seen [37]. It is also known as congenital lobar emphysema, though no damage to the alveolar wall is appreciated [37].

CLO can be idiopathic in about 50 % of cases [63]. The remaining 50 % can be extrinsic or intrinsic in origin. Intrinsic factors include cartilaginous deficiency, bronchial stenosis/atresia, or mucus plugs. Extrinsic causes include extrinsic compression from an extrabronchial mass or vascular structure such as dilated pulmonary arteries in tetralogy of Fallot with the absent pulmonary valve (Fig. 9.11).

CLO is characterized as an area of increased T2 signal with a lobar distribution; it is usually more homogeneous than CPAM and less hyperintense when compared to BPS [48]. Lung structure appears intact with stretched hilar vessels [64].

When the overinflated lung is large, mediastinal shift and adjacent normal lung compression can occur [65], and herniation of the overinflated lung can be seen to the contralateral side [66].

Echocardiogram should be performed to exclude congenital heart disease. 14 % of patients have an associated cardiac anomaly, most likely a large left to right shunt with pulmonary hypertension [65].

Prenatal outcome varies from spontaneous resolution to progression with increase in size and increased intrathoracic pressure resulting in impaired fetal circulation and swallowing with hydrops and polyhydramnios. Occasionally, resolution is suspected prenatally, but a persistent, nonvisualized mass could result in neonatal respiratory insufficiency due to presence of overinflation and valve mechanism [63].

The main indicator of prenatal outcome is the presence of hydrops, and follow-up examinations should be performed to assess changes and presence of hydrops.

The presence of pleural fluid is considered abnormal in the fetus. It can be seen in isolation or in association with a lesion, such as CPAM, BPS, lymphangiectasia, cardiac anomalies, infections including TORCH, and chromosomal abnormalities like Turner syndrome and trisomy 21.

Hydrothorax can be primary or secondary. Primary hydrothorax is rare and affects males more frequently. It results from an anomaly in the development of the lymphatic system resulting in chylous leak into the pleural space and can be unilateral or bilateral [67, 68]. Primary effusions are characterized by having high pressures, resolving rapidly after thoracentesis and developing hydrops restricted to the upper fetal body [68]. Secondary hydrothorax is seen in hydrops-related pathologies or pulmonary masses that can cause mass effect and compression.

When a hydrothorax is present, MRI demonstrates an area of bright T2 signal surrounding the lung parenchyma. It can be small or large and unilateral or bilateral and can remain stable, resolve, or progress to hydrops. Depending on the size, mediastinal shift and lung compression can occur (Fig. 9.12). MRI may help identify associated abnormalities not seen by ultrasound, like an inconspicuous CPAM or BPS.

Depending in the content of the pleural fluid (lipid, protein, or blood products), different signal intensities might be seen with MRI in both T1- and T2-weighted images that may help establish the etiological diagnosis [7].