Pediatric Chest: A Review of the Must-know Diagnoses

Shreya Sood, MD; Julia Rissmiller, MD; Anastasia Hryhorczuk, MD

Disclosures

Appl Radiol. 2018;47(4):4-14. 

In This Article

Congenital Parenchymal Lesions

While congenital lung lesions may not be routinely encountered in daily imaging, they are common considerations in diagnostic pediatric radiology. Early recognition is crucial to prevent misdiagnosis and mismanagement.

Congenital thoracic lesions are thought to originate from disturbances during the embryogenesis of lung and airway development. The imaging appearances of these lesions often demonstrates significant overlap. In fact, even on histopathologic analysis, these lesions may share similar characteristics, as some are truly hybrid entities. In current radiologic and pathologic analyses, congenital lung lesions are regarded as a continuous spectrum of developmental abnormalities, from cystic airway lesions to mixed cystic airway/vascular lesions to purely vascular lesions.

As our understanding evolves, so do the nomenclature and classification of these entities. Under this umbrella, the most commonly described congenital chest lesions are congenital pulmonary airway malformations (CPAM), bronchopulmonary sequestrations (BPS), bronchogenic cysts, and congenital lobar overinflation (CLO). Among these, CPAM and BPS most commonly present as hybrid lesions. These lesions are now routinely detected on fetal ultrasounds and are often identified prior to birth. While the appearance of congenial lung masses on fetal imaging is beyond the scope of this paper, most of these entities present as hyperechoic, space occupying masses, which shift the mediastinal contents away from the involved hemithorax on fetal sonography.

Congenital Pulmonary Airway Malformations

Formerly termed congenital cystic adenomatoid malformation, this lesion is now more aptly called congenital pulmonary airway malformation (CPAM) to encompass the gamut of histological appearances. CPAM is the most commonly encountered congenital cystic lesion,[1] thought to result from abnormal branching of immature bronchioles during lung development. The incidence is likely underestimated at 1 in 25,000 to 1 in 35,000 live births.[2]

CPAMs are hamartomatous anomalies that communicate with the tracheobronchial tree.[3] Histologically, these lesions look like terminal bronchioles lined with respiratory epithelium, lacking cartilage or bronchial glands.[1] The exact insult causing this abnormality and the precise timing of its development are unknown; it may form anywhere between 5–22 weeks gestation. Pure, non-hybrid, CPAMs have normal arterial and venous connections to the pulmonary circulation. Hybrid CPAMs that occur concomitantly with abnormal vascular connections feeding or draining the lung lesions may occur alongside additional abnormalities, including congenital heart disease and neural tube defects. Not surprisingly, patients with these additional associations have a higher incidence of stillborn birth.[4]

CPAMs may contain larger cysts greater than 2 cm, smaller cysts between 0.5 and 2 cm, or microcysts, which may create the appearance of a solid mass on imaging. The vast majority of these lesions are solitary, with a lower lobe predilection.[5] When bilateral CPAMs are present, there is a higher risk of congenital high airway obstruction syndrome (CHAOS).[5] CPAMs often present with respiratory symptoms including tachypnea, retractions, and cyanosis within first month of life.[4,5,6] Fewer than 10% present after one year of age.[5] Later presentations include recurrent or persistent pneumonia (most common), lung abscess, pneumothorax, reactive airway disease or, rarely, malignant transformation. Some CPAMs may regress, especially the microcystic type.[2]

On radiographs, CPAMs are hyperlucent and multicystic, with occasional solid components. Large lesions may cause lung hyperexpansion with mediastinal shift or flattening of the hemidiaphragm (Figure 1). Air-fluid levels may be seen secondary to residual fluid in the initial postnatal period. In older patients, air-fluid levels typically reflect the sequelae of resolving infection. When older patients present with infected CPAMs, it is important to differentiate these lesions from necrotizing pneumonia, with findings including hyperexpanded lungs and a lack of air bronchograms favoring an infected CPAM. Computed tomography angiography (CTA) is essential in distinguishing these lesions from other congenital lung lesions, as the presence of a systemic feeding vessel may herald a hybrid lesion or sequestration. This vessel must be recognized prior to surgical intervention.

Figure 1.

4-month-old male infant with respiratory distress. (A) AP supine chest x-ray demonstrates hyperexpanded right hemothorax with underlying cystic, lucent lesions causing flattening of the right hemidiaphragm and leftward mediastinal shift. There is mild compressive atelectasis of the left lung. Axial (B) and coronal (C) CT images in lung window demonstrating a large multicystic lesion in right lower lobe with one large cyst and several smaller cysts occupying right hemithorax. There is mass effect on the mediastinum and left lung alongside left lower lobe subsegmental atelectasis. Findings are compatible with congenital pulmonary airway malformation (CPAM).

Treatment of CPAMs involves surgical resection, either via lobectomy or segmental resection, if multiple lesions are present.[2] Early surgery prevents infection and reduces the rarer risk of malignancy, which has been identified as early as 13 months of age.[7] Associated malignancies include embryonal rhabdomyosarcoma, pleuropulmonary blastoma and bronchoalveolar carcinoma.[8–10]

Bronchopulmonary Sequestrations

Bronchopulmonary sequestrations (BPS) are composed of nonfunctioning pulmonary tissue that lacks communication with the tracheobronchial tree, possibly originating from a supernumerary lung bud.[5] These lesions characteristically have a systemic arterial supply arising from vessels including the thoracoabdominal aorta, splanchnic vessels, or rarely, coronary arteries (Figure 2). Sequestrations may be asymptomatic or present with respiratory distress, infection, feeding difficulties or even, rarely, congestive heart failure.[11]

Figure 2.

1-year-old female with abnormal chest radiograph. Contrast-enhanced CT (CECT) of the chest in soft-tissue mediastinal windows demonstrates a soft-tissue lesion in left lower lobe (*) supplied by an anomalous feeding vessel (arrowhead) arising from the celiac axis (long arrow), compatible with bronchopulmonary sequestration (BPS).

There are two commonly described subtypes of BPS: extralobar and intralobar (Table 1). Extralobar sequestrations are discrete and invested in their own separate pleura. They are typically located in the left lower chest, but can be also be within or below diaphragm. Typically, these lesions demonstrate systemic venous drainage to the superior vena cava or azygos veins. In some case, extralobar sequestrations may be associated with other congenital abnormalities, including congenital diaphragmatic hernias and CPAMs.[5] Intralobar sequestrations are closely associated with adjacent lung, demonstrate pulmonary venous drainage, and are generally isolated without other associations. This subtype presents in later childhood.

Sequestrations may sometimes be visible in neonatal period via ultrasound, as well-defined, homogeneous, isoechoic masses. Color Doppler may demonstrate the pathognomonic systemic blood supply. Presence of concurrent cysts may suggest a hybrid lesion. The two subtypes of sequestration cannot be reliably distinguished on imaging unless a pleural effusion surrounds the extralobar sequestration or if the sequestration occurs in upper abdomen and is, by definition, extralobar. An upper abdominal extralobar sequestration must be distinguished from a suprarenal neuroblastoma, which lacks systemic arterial supply and demonstrates metaiodobenzylguanidine (MIBG) uptake on nuclear scintigraphy.

On CT scans, sequestrations may be homogeneous or heterogeneous masses, sometimes with cystic changes. Characteristically, these are solid lesions surrounded by peripheral emphysematous changes. MRI/MRA chest may also be performed to assess these lesions. However, CT is generally preferred due to better resolution of lung parenchymal findings.

Some sequestrations regress postnatally, but symptomatic infants are managed surgically.[2] Asymptomatic lesions are should be adequately characterized by cross-sectional imaging to define the feeding vessel then electively resected in order to minimize risk of infection or hemorrhage.

Congenital Lobar Overinflation

Congenital lobar overinflation (CLO) was previously termed "congenital lobar emphysema"—a misnomer, since these lesions lack the destruction of alveolar walls that typically denotes 'emphysema'. Typically, CLO affects a single lobe of the lung, although multiple lobes or segments within a lobe may be affected. In decreasing frequency, the most commonly affected lobes are: left upper, right middle and right upper lobes.[12] CLO arises due to narrowing of the airway lumen, followed by subsequent obstruction from various etiologies such as endobronchial lesions (e.g. mucosal webs), extrinsic compression from vascular anomalies or congenital deficiency of bronchial cartilage and ensuing bronchomalacia.[13] The obstructed region becomes hyperinflated from collateral drift through check-valve mechanism at the level of the bronchus, with a greater amount of air entering on inspiration than exiting on expiration. CLO is sometimes associated with congenital heart disease, namely, patent ductus arteriosus (PDA) and ventricular septal defect (VSD).[12]

Diagnosis is made via radiography and computed tomography (CT). CLOs tend to be symptomatic lesions, presenting with respiratory distress in early life. At birth, these lesions may be may be fluid-filled and radiopaque. As fluid is reabsorbed, lesions may first demonstrate interstitial reticulation and, finally, become hyperlucent once significant air trapping occurs. There may be associated mass effect with contralateral atelectasis, flattening of hemidiaphgram and increased rib spacing in affected lobe (Figure 3). Vessels will be attenuated, and CLO must be differentiated from pneumothoraces which demonstrate a pleural line and lack bronchovascular markings. Most lesions are treated via lobectomy to allow normal lung development and symptomatic relief.[14]

Figure 3.

Infant female with respiratory distress. (A) Chest x-ray performed at 1 month-20 days of age demonstrates hyper-expanded right middle lung (arrow) with associated widening of the intercostal rib spaces. There is associated mild shift of the heart towards the left hemithorax. (B) This chest CECT was performed at 6 months of age. Axial slice in lung windows demonstrates a hyperaerated right middle lobe with mild compressive atelectasis of right lower lobe and atelectasis in left lower lobe. Findings are compatible with congenital lobar overinflation (CLO).

Bronchial Atresia

Unlike the previously described thoracic abnormalities, bronchial atresia is rarely detected prenatally. Most often, these are discovered due to recurrent symptoms or identified incidentally. Bronchial atresia occurs due to obliteration of a focal segment of bronchus, with normal development of the more distal lung.[15] Most commonly, this affects bronchial structures at the level of the segmental/subsegmental bronchus.[15] If bronchial atresia occurs centrally, at the level of the mainstem bronchus, it is usually lethal in utero or the immediate postnatal period.

Peripheral bronchial atresias present in older children due to recurrent infections. Radiographs may demonstrate an overinflated portion of lung. A bronchocele may be identified distal to the atretic bronchus, appearing as a fluid-filled, tubular, branching structure, finding which is considered pathognomonic for bronchial atresias. Symptomatic atresias that serve as a nidus for recurrent infections are surgically removed. Incidental, asymptomatic atresias may not require intervention.

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