Congenital lung malformations (CLMs) encompass various developmental anomalies affecting the lungs, airways, and vasculature [23]. Clinical presentations range from asymptomatic cases to severe respiratory distress or recurrent infections [23]. Improved prenatal imaging techniques (not discussed herein due to limited relevance to general radiologists), namely obstetric ultrasonography (US) and fetal MRI, contribute to the growing prenatal diagnosis of CLM [23, 24]. CR is often the initial screening modality for postnatal CLM detection, despite its relatively low sensitivity [23, 25]. Suspicion arises when persistent opacities or lucencies are observed within the same lobe in children with recurrent infections [25]. In most instances, further characterisation and surgical planning necessitate additional cross-sectional imaging, typically contrast-enhanced CT (CECT) or contrast-enhanced MRI (CEMRI) [23, 26,27,28,29].

Congenital pulmonary airway malformation (CPAM) is the most common type of CLM, with an estimated incidence of 1 per 8300 live births [23]. CPAM arises from abnormal bronchoalveolar tree development due to hamartomatous proliferation [23]. Histopathologically, CPAM is classified into five types according to the Stocker classification with the most common including: Type 1 (cysts > 2 cm) representing 50–70% of cases, Type 2 (cysts < 2 cm) accounting for 15–30% of cases, and Type 3 (microcystic < 5 mm) representing 5–10% of cases [23]. The latter can also present as a solid mass, often resulting in mediastinal shift, which complicates differentiation from pleuropulmonary blastoma (PPB), a malignant tumour associated with CPAM [23]. PPB is classified into three types: Type 1 (cystic), Type 2 (mixed cystic and solid), and Type 3 (completely solid) [23]. Differentiating Type 1 PPB from CPAM Type 4, which exhibits large cysts typically greater than 10 cm, is particularly challenging [23]. Currently, testing for somatic mutations in DICER1 is used to assess potential malignancy predisposition, with DICER1 heterozygous germline mutations present in up to 66% of PPB [23]. Additionally, CPAM is associated with other tumours, such as adenocarcinomas and squamous cell carcinoma, both linked to mucinous cell degeneration and KRAS gene mutations, one of the most frequently mutated genes in lung cancer [23].

Imaging plays a crucial role in both diagnosis and presurgical assessment of CPAM [23, 25,26,27,28,29]. On CR, CPAM may appear as a focal opacity with fluid-filled cysts (Fig. 5A) [25]. Resorption of amniotic fluid alters radiographic appearances, resulting in lucent air-filled masses with or without compression of surrounding lung parenchyma and mediastinum [25]. CECT at 2 months of age is the gold standard for defining CPAM size, location, and vascular supply, aiding thoracic surgeons in surgical planning (Fig. 5B) [23, 26]. Dedicated radiology reports are available to summarise crucial CPAM features [30]. MRI for assessment of CPAM characteristics carries the advantages of evaluating vascular supply without contrast use and enabling long-term follow-up of asymptomatic children without radiation exposure [27,28,29]. Treatment strategies for CPAM vary among paediatric surgeons, with some advocating for early surgery in the first year of life to promote compensatory lung parenchymal growth and prevent complications from recurrent infections [23]. Those in favour of early surgery also consider the unclear risk of malignant transformation in CPAM [23]. Alternatively, a watch-and-wait strategy with long-term follow-up in asymptomatic cases may be preferred, as invasive surgery and general anaesthesia may have negative effects on long-term neurodevelopment and some potentially serious or even life-threatening complications [23]. Timing of resection is still debated; some surgeons prefer earlier surgery, by 4 months of age and some as late as 1 year of age, although delayed resection has not shown improved outcomes [23].

Mixed lesion comprising congenital pulmonary airway malformation (CPAM) type 2 and Intralobar sequestration (ILS) in a 1-week-old girl. A Antero-posterior (AP) chest radiograph revealing a poorly defined lesion in the right lung base (thin arrow in A). B CT, coronal plane, lung window, highlighting multiple cysts smaller than 2 cm associated with the CPAM type 2 component (thick arrow). C CECT, mediastinal window displaying a soft tissue-enhancing lung lesion in the right lower lobe (arrowhead), supplied by the descending aorta and draining through the pulmonary vein (not shown)

Bronchopulmonary sequestration (BPS) is the second most common CLM, with an estimated incidence of 1 to 10 in 35,000 live births [23]. It presents as a dysplastic segment or lung lobe, not linked to the tracheobronchial system, with a blood supply from a systemic artery instead of the pulmonary artery and draining via the pulmonary or systemic veins [23]. BPS is categorised into intra- (ILS, 75% cases) and extra-lobar (ELS, 25% cases) based on arterial and venous supply and the presence of separate visceral pleura [23]. ILS appears within the visceral pleura and is supplied by one or multiple aberrant arteries originating from the descending thoracic aorta, typically branching to the lower lobe (the most common location) [23]. The venous drainage of ILS is often to the left atrium through the pulmonary veins. Conversely, ELS is covered by a distinct pleura and receives its arterial supply from the thoraco-abdominal aorta, including visceral abdominal arteries (i.e., coeliac artery) [23]. ELS venous drainage occurs through the portal vein or the systemic azygos or hemiazygos veins into the inferior vena cava and then to the right atrium. ELS is usually located in the thoracic cavity but can also develop below the diaphragm in the abdomen (subdiaphragmatic ELS) [23]. ELS often presents early in life with symptoms like respiratory distress, cyanosis, and recurrent infections, while ILS typically manifests later with recurrent infections in the same pulmonary lobe [23].

Imaging is pivotal for diagnosis and surgical planning, particularly when echocardiography indicates significant shunting with the risk of congestive heart failure [23, 26]. CR reveals nonspecific findings, including focal opacity, primarily in the lower lobes, in patients with recurrent infections [25]. Cystic lesions may be visible in cases of combined BPS and CPAM, termed “mixed/hybrid lesions” (Fig. 5C) [23, 26]. CECT determines arterial and venous supplies, location, size, and potential coexistence of CPAM [23, 26]. CEMRI as an alternative is more challenging due to anaesthesia requirement and longer scan duration, and is performed only in specialised centres [27,28,29].

Congenital lobar overinflation (CLO) involves focal or segmental lung overinflation without wall destruction, often due to bronchial obstruction (ball-valve mechanism) [23, 31]. Bronchial obstruction may be caused by intrinsic factors, such as the absence of bronchial cartilage, bronchial stenosis, or bronchomalacia, or by extrinsic factors, such as a vascular ring. However, in 50% of patients, CLO is idiopathic, and a clear cause cannot be identified [23]. It most commonly affects the left upper lobe (40–45% cases), followed by the right middle (30% cases), right upper (20% cases), and lower lobes (5% cases). The historical prevalence of CLO was estimated to be approximately 1 in 20,000 to 30,000. This was during a time when first-generation CT scanners could not reliably differentiate between CLO and bronchial atresia. In recent studies, it has been shown that CLO can constitute up to 10% of CLM, with a higher incidence in males, demonstrating a male-to-female ratio of 3:1 [23, 31]. Children with CLO are typically symptomatic in the neonatal period and within the first year of life, presenting with progressive hyperinflation of the affected lobe [23]. This can lead to rapidly developing respiratory distress, often due to concurring mediastinal shift and compression of surrounding lung parenchyma (Fig. 6A–C). Diagnosis relies on imaging, which also guides surgery in symptomatic patients [23, 26, 31].

Comparison of congenital lobar overinflation (CLO) and bronchial atresia (BA) in children. A Chest radiograph, (B) coronal CT lung window image of a 3-year-old girl, and (C) a follow-up CT at 12 years. Notice the left upper lung lucency and asymmetric expansion compared to the right (arrow in A), corresponding to hyperinflated left upper lobe on the CT at the same age (arrowhead in B). By age 12, the patient presents with symptomatic progressive hyperinflation of the left upper lobe (thick arrow in C). D Post contrast CT, coronal plane, mediastinum window and (E) coronal plane, lung window and (F) coronal T2-weighted single-shot fast spin echo MRI in a 7-year-old boy with bronchial atresia in the apical segment of the left lower lobe. Observe the bronchocele with soft tissue density (arrow in D), hyperinflation of the apical segment of the lower lobe displaying lower density (arrowhead in E), and increased T2 signal on MRI indicating mucus within the bronchocele (thick arrow in F)

On CR, CLO typically presents as a large lucent lung segment or lobe causing compression and displacement of adjacent structures, namely the diaphragm or mediastinum (Fig. 6A–C) [25, 26]. Initial postnatal CR may show diffuse opacification with mass effect due to retained fluid, resolving in follow-up radiographs [25, 26]. CT reveals a low-attenuation region with hyperinflated lung parenchyma involving a segment or entire lobe (Fig. 6A–C) [23, 26]. MRI with conventional MR sequences to assess CLO is challenging because increased air content does not produce signal [27,28,29], and distinguishing CLO from CPAM on MRI can be difficult if cyst walls are not clearly visualised [27,28,29].

Bronchial atresia (BA) occurs due to focal obliteration of (sub-)segmental bronchi, leading to hyperinflation of the lung distal to the obstruction via collateral ventilation through the pores of Kohn and channels of Lambert [23, 26]. The Pores of Kohn typically become well developed by the age of 3 to 4 years, while the Channels of Lambert reach full development around 6 to 8 years of age. This developmental timeline helps explain why progressive hyperinflation of lung parenchyma surrounding the BA is more commonly observed in older children. BA carries an estimated prevalence of 1.2 cases per 100,000 live births. Despite presenting as an isolated abnormality on imaging, on pathology examination, it often coexists with other CLM, especially CPAM and BPS [23, 26, 32]. Most BA patients are asymptomatic, often diagnosed incidentally in adulthood, although recurrent infections may occur [23, 26].

Radiographically, BA presents with segmental hyperinflation like CLO, albeit usually to a lesser extent [25, 26] (Fig. 6D–F). Accumulation of mucus in the obstructed bronchus (bronchocele) may manifest as a tubular opacity (Fig. 6D–F) [25]. CT reveals segmental or lobar hyperinflated and low-attenuating lung parenchyma, with or without bronchocele (Fig. 6D–F) [26]. MRI, offering a clear depiction of the high T2 signal within the bronchocele, serves as an alternative to CT (Fig. 6D–F) in specialised centres [27]. Differential diagnosis includes CPAM, which has cystic components rather than overinflation, and CLO, which is typically larger in size and without a bronchocele [23, 26].

Congenital diaphragmatic hernias (CDH) result from defective diaphragm formation, causing abdominal structures to herniate into the chest, leading to parenchymal compression and lung hypoplasia [33]. CDH is mainly diagnosed prenatally, typically affecting the posterior hemidiaphragm (Bochdalek hernia), located predominantly on the left side (95% cases) [33]. Anterior hernias (Morgagni) are rarer (less than 5%), smaller than Bochdalek hernias, and usually not associated with lung hypoplasia [33]. Right-sided hernias exhibit more severe symptoms and poorer outcomes due to liver herniation [34]. Prenatal imaging plays an important role in CDH assessment and quantifies fetal lung volume for postnatal prognosis [24, 34].

Postnatal CR reveals intrathoracic air-filled bowel loops, mediastinal shift, and, in left-sided hernias, an abnormal feeding tube position when the stomach is herniated in the thorax [34]. Postnatal LUS assesses herniated contents presurgically and aids postoperative follow-up [34]. CT or MRI is usually not necessary for surgical planning. For CDH recurrence assessment, CR with two projections (AP or PA and lateral view) is recommended [34] (Fig. 7A). If CR findings are inconclusive, non-contrast T2-weighted MRI or CECT can confirm recurrence (Fig. 7D). CECT is instrumental in evaluating herniated organs and identifying potential complications, such as bowel loop incarceration, adhesions, and volvulus, which occur in approximately 20% of patients with recurrent CDH [34] (Fig. 7). In cases of recurrence, contrast is administered intravenously to assess wall enhancement in incarcerated bowel loops and exclude necrosis [