Imaging in Pulmonary Interstitial Emphysema 

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Pulmonary interstitial emphysema (PIE) is an iatrogenic pulmonary condition of the premature infant with immature lungs. PIE occurs almost exclusively in association with respiratory distress syndrome and mechanical ventilation. ^[1]  Independent risk factors for mechanical ventilation-caused pulmonary interstitial emphysema are higher oxygen during resuscitation and a higher need for surfactant and ventilatory pressures before diagnosis. ^[2]

The ventilatory pressure that is used to keep the alveolar ducts open also may cause the alveolar duct to rupture (usually at the junction of the bronchiole and alveolar duct); this in turn leads to the escape of air into the pulmonary interstitium, lymphatics, and venous circulation. ^{[3, 4, 5]}

PIE may be identified with a frontal chest radiograph. Disease progression is assessed with sequential studies. ^[6] In an ill infant, it may be difficult to differentiate PIE from lucent overdistention of the bronchioles, although overdistended distal airways tend to be round and of uniform diameter, whereas PIE tends to be ovoid in the direction of the bronchovascular bundles. In addition, the lesions of PIE tend to be of different sizes. It is also difficult to differentiate PIE from early bronchopulmonary dysplasia (BPD) with uneven patterns of aeration. Computed tomography (CT) scanning of the chest can be a helpful diagnostic tool if doubt about the diagnosis remains. The presence of subpleural PIE, in which there is an interstitial air collection in the subpleural region of the lungs excluding the bronchovascular bundle, on CT scan suggests single or multiple alveolar rupture(s) as an origin of pneumomediastinal air. ^[6]  A study by Donnelly et al found that 82% of patients with persistent pulmonary interstitial emphysema (14 of 17 patients) had characteristic CT findings (central lines and dots surrounded by radiolucency). ^[7]   

The development of PIE is demonstrated in the images below.

On radiography, PIE appears as linear, oval, and occasional spherical cystic air-containing spaces throughout the lung parenchyma. The interstitial changes are initially linear but may become more cystic as the air in the interstitium congregates locally. Subpleural cysts also develop and may rupture, producing a pneumothorax. The heart tends to get smaller as intrathoracic pressure increases; this results in diminished venous return into the chest. Overall lung volume is increased; however, the lungs are less compliant because they are splinted at a large volume by the air within the interstitium. Gas exchange is reduced by the increase in distance between the pulmonary vascular bed and the airspaces.

Linear gas collections in the periphery of the lung, in association with an increased demand for respiratory support, are diagnostic of PIE. Increasing lung volumes also strongly support a diagnosis of PIE. Early bronchopulmonary dysplasia (BPD) may present as focal areas of hyperaeration secondary to partial bronchial obstruction. The pattern closely resembles PIE, although the lucency is less linear in BPD. At histopathology, many lungs of infants with BPD demonstrate PIE that was not seen radiographically.

The images below demonstrate the radiographic characteristics of PIE.

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Nuñez-Ramiro A, Aguar M, Cernada M, Parra-Llorca A, Vento M. Oxygen needs during resuscitation and surfactant to achieve stabilisation were independent risks factors for pulmonary interstitial emphysema in preterm infants. Acta Paediatr. 2018 Jan. 107 (1):28-32. [Medline].

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Heneghan MA, Sosulski R, Alarcon MB. Early pulmonary interstitial emphysema in the newborn: a grave prognostic sign. Clin Pediatr (Phila). 1987 Jul. 26(7):361-5. [Medline].

Morisot C, Kacet N, Bouchez MC, Rouland V, Dubos JP, Gremillet C, et al. Risk factors for fatal pulmonary interstitial emphysema in neonates. Eur J Pediatr. 1990 Apr. 149(7):493-5. [Medline].

Yu VY, Wong PY, Bajuk B, Szymonowicz W. Pulmonary interstitial emphysema in infants less than 1000 g at birth. Aust Paediatr J. 1986 Aug. 22(3):189-92. [Medline].

Barcia SM, Kukreja J, Jones KD. Pulmonary interstitial emphysema in adults: a clinicopathologic study of 53 lung explants. Am J Surg Pathol. 2014 Mar. 38 (3):339-45. [Medline].

Kim HR, Yoo SM, Lee HY, Han JH, Frazier AA, White CS. Presence of subpleural pulmonary interstitial emphysema as an indication of single or multiple alveolar ruptures on CT in patients with spontaneous pneumomediastinum. Acta Radiol. 2016 Dec. 57 (12):1483-1489. [Medline].

Beverly P Wood, MD, MSEd, PhD Professor Emerita of Radiology and Pediatrics, Division of Medical Education, Keck School of Medicine, University of Southern California; Professor of Radiology, Loma Linda University School of Medicine

Beverly P Wood, MD, MSEd, PhD is a member of the following medical societies: American Academy of Pediatrics, Association of University Radiologists, American Association for Women Radiologists, American College of Radiology, American Institute of Ultrasound in Medicine, American Medical Association, American Roentgen Ray Society, Radiological Society of North America, Society for Pediatric Radiology

Disclosure: Nothing to disclose.

Bernard D Coombs, MB, ChB, PhD Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand

Disclosure: Nothing to disclose.

John Karani, MBBS, FRCR Clinical Director of Radiology and Consultant Radiologist, Department of Radiology, King’s College Hospital, UK

John Karani, MBBS, FRCR is a member of the following medical societies: British Institute of Radiology, Radiological Society of North America, Royal College of Radiologists, Cardiovascular and Interventional Radiological Society of Europe, European Society of Radiology, European Society of Gastrointestinal and Abdominal Radiology, British Society of Interventional Radiology

Disclosure: Nothing to disclose.

Imaging in Pulmonary Interstitial Emphysema 

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