▶ AP chest radiograph of the newborn (left) shows an endotracheal tube and hyperexpanded but dense right middle lobe (arrowhead).
▶ Chest radiograph obtained 2 days later (right) shows increased expansion of the right middle lobe (arrowheads), which is now hyperlucent and extends across the midline. Atelectasis of the left lung and right upper and lower lobes (arrows) is now observed.
CLH may be mistaken for pneumothorax, but the configuration of an expanded lobe, lack of collapsed lung at the hilum, and lung markings distinguish CLH. Another consideration in the neonate is large cyst congenital pulmonary airway malformation.
▶ Congenital lobar hyperinflation, except for the rare polyalveolar variant, is not a specific malformation, but the result of bronchial narrowing. This narrowing may be due to an intrinsic abnormality such as bronchostenosis or may be due to extrinsic compression, for example by a crossing vessel. The latter likely explains the association with congenital heart disease.
▶ The abnormality usually affects one of the upper lobes or the right middle lobe.
▶ Airways are slightly larger in inhalation, due to the negative pressure in the chest. Due to the narrowing of the bronchus in CLH, air is able to enter the lobe in inhalation but not to leave in exhalation, leading to progressive over-expansion of the lobe. The narrowed bronchus also causes delay in the clearance of lung fluid postnatally, so the lobe is initially opaque but becomes progressively more lucent.
▶ On CT, the over-expanded, radiolucent lobe is seen to contain attenuated vessels at the periphery of alveoli and no soft-tissue components. CT is helpful to evaluate for an extrinsic cause such as mediastinal mass.
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