You are in: eMedicine Specialties > Radiology > PEDIATRICS Pulmonary Interstitial EmphysemaArticle Last Updated: Jun 18, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 7
  Author: Beverly P Wood, MD, MS, PhD, Professor, Departments of Radiology and Pediatrics, Division of Medical Education, Keck School of Medicine, University of Southern California Beverly P Wood is a member of the following medical societies: American Academy of Pediatrics, American Association for Women Radiologists, American College of Radiology, American Institute of Ultrasound in Medicine, American Medical Association, American Roentgen Ray Society, Association of University Radiologists, Radiological Society of North America, and Society for Pediatric Radiology Editors: Robert J Starshak, MD, Medical Director, Assistant Clinical Professor, Department of Radiology, Medical College of Wisconsin, Falls Medical Group; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; John Karani, MBBS, FRCR, Consulting Staff, Department of Radiology, King's College Hospital, London Author and Editor Disclosure Synonyms and related keywords: acquired cystic lung disease of the premature infant, barotrauma of the premature lung interstitium, PIE INTRODUCTIONSection 2 of 7
  BackgroundPulmonary interstitial emphysema (PIE) is an iatrogenic pulmonary condition of the premature infant with immature lungs. PIE occurs almost exclusively in association with mechanical ventilation. The ventilatory pressure 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.1, 2 PathophysiologyImmature lungs are underdeveloped and lack adequate surfactant to keep the alveolar ducts and early alveoli open on inspiration and expiration. As a result of the decrease in surface area, the capacity to transfer gas is reduced; this, in conjunction with widespread atelectasis, leads to inadequate transfer of carbon dioxide and oxygen across the epithelial surfaces to the pulmonary microvascular system. Methods to improve oxygen saturation include administering high concentrations of oxygen and expanding and maintaining the expansion of gas-exchanging surfaces of the lung using high levels of inhaled oxygen and positive pressure ventilation. Excessive intra-airway pressure may cause gas to leak from the alveolar ducts (primordial acini) into the lung interstitium. Once in the interstitium, the gas is picked up in the rich lymphatic network of the neonate and is carried toward the pleural lymphatics and central bronchopleural lymphatics. PIE usually occurs early during ventilation; most infants with PIE present in the first 72 hours. PIE occurs less frequently now because immature babies are treated with exogenous surfactant; such treatment increases lung compliance (thus reducing the need for ventilatory pressure) and keeps the alveolar ducts open during both inspiration and expiration.3 It also assists in the recruitment of alveolar ducts to prevent areas of overinflation and underinflation. Currently, PIE is seen more often in infants with bronchopulmonary dysplasia (BPD) who receive long-term ventilator therapy with uneven aeration; in such patients, PIE results from air trapping and airspace rupture. FrequencyUnited StatesSeveral decades ago, PIE was a common occurrence in infants with severe respiratory distress on ventilators. Currently, it is an uncommon occurrence because of treatment with surfactant and gentle ventilation, as well as the availability of high-frequency oscillatory ventilation for infants who are difficult to maintain with conventional ventilation. Mortality/MorbidityIn the past, the mortality associated with PIE was high because the lungs became stiff and gas freely dissected into the interstitium, where oxygen absorption was poor. With rapid measures of prevention and alternative ventilatory improvement, approximately 25% of the infants survived, but all developed severe BPD.
SexPIE is seen with equal frequency in both sexes. AgePIE is seen in premature infants usually younger than 32 weeks' gestation and who weigh less than 1200 g. PIE occurs in the first 72 hours of life, although it may be observed as a complication of prolonged positive pressure ventilation in the older premature infant. AnatomyPIE may occur diffusely throughout the lung, or it may be unilateral or lobar in occurrence. When PIE is local, the surrounding lung is often compressed as the region with PIE enlarges. The lesion of PIE is mechanical distention (and overdistention) of the alveolar ducts (precursors to alveoli and acini), which causes the ducts to rupture; alternatively, rupture occurs at the relatively weak junction of the alveolar duct and its bronchiole. After rupture, the air leak persists with the pressure of ventilation and motion of respiration. Gas is free to dissect into the interstitium, where it may remain or be taken up by the pulmonary lymphatic system. Cysts and overdistention of the lung reflect the effect of gas within the interstitium. Clinical DetailsPIE develops in infants who have established pulmonary disease of prematurity with respiratory distress syndrome who are being treated with supplemental oxygen, endotracheal intubation, and positive pressure mechanical ventilation. Most premature infants at risk for respiratory distress syndrome are treated with endotracheal surfactant, which improves pulmonary expansion, lung compliance, and oxygen exchange. PIE often occurs rapidly, arising in one region of the lung and quickly involving multiple lobes with fixed hyperexpansion, causing the clinical condition to worsen. Oxygen saturation of the blood falls, and ventilatory requirements increase.4 Emergent management takes several forms: initiation of high-frequency oscillatory ventilation with the rapid exchange of low volumes of gas at low pressure and, if PIE is localized, selective intubation of the airway bypassing the bronchus to the involved lobe.5, 6 Preferred ExaminationClinical examination involves the evaluation of pH and arterial oxygen saturation in proportion to the fraction of inspired oxygen. PIE may be identified with a frontal chest radiograph. Disease progression is assessed with sequential studies.8 Limitations of TechniquesIn an ill infant, it may be difficult to differentiate PIE from lucent overdistention of the bronchioles, though 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 BPD with uneven patterns of aeration. DIFFERENTIALSSection 3 of 7
Bronchopulmonary Dysplasia Hyaline Membrane Disease RADIOGRAPHSection 4 of 7
FindingsOn 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 (see Images 1-12). Degree of ConfidenceLinear 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. False Positives/NegativesEarly 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. INTERVENTIONSection 5 of 7
When PIE is localized, it is extremely helpful to selectively ventilate unaffected lung so as to bypass the affected lobe or lobes. Radiologic imaging can assist by determining the location of the endotracheal tube. Radiologic imaging is also useful in monitoring for the potential complication of pneumothorax. Placing the infant in the decubitus position with the affected side down can be of help when the diagnosis of unilateral PIE is made.9, 10, 11, 12 Medical/Legal Pitfalls
See also the Medscape topic Medical Malpractice and Legal Issues. MULTIMEDIASection 6 of 7
REFERENCESSection 7 of 7
Pulmonary Interstitial Emphysema excerpt Article Last Updated: Jun 18, 2008 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
