When an alveolus or terminal airway ruptures, air escapes into the pulmonary interstitium and results in pulmonary interstitial emphysema (PIE). This occurs most often in newborns with severe surfactant-deficiency disease. Gas may travel into bronchovascular sheaths or lymphatic channels and produce pneumothorax, pneumomediastinum, or pneumopericardium.
        Radiographically, PIE appears as cystic lucencies or bizarre tubular lucencies that fail to conform to the branching pattern of air bronchograms [1-3]. It may be focal or diffuse, unilateral or bilateral.
        One form of localized PIE, which manifests as single or multiple well defined cystic air collections, is called  pseudocysts [4].
        PIE can be persistent. When PIE lasts more than 1 week, it is called persistent pulmonary interstitial emphysema. Localized persistent pulmonary interstitial emphysema is an expansile, multicystic lesion in chest radiographs [1].

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Figure 1. Note tubular lucencies in the right lung.
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Figure 2. Note cystic and tubular lucencies in the right
lower lung.
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Figure 3. Note cystic and tubular lucencies in the
left lung, the anterior pneumothorax in the left lower
chest and air peripheral to the left lung edge.

REFERENCES
1. Donnelly LF, Frush DP. Localized radiolucent chest lesions in neonates: causes and differentiation. AJR 1999;172:1651-8.
2. Hernanz-Schulman M. Cysts and cystlike lesions of the lung. Radiol Clin North Am 1993;31(3):631-49.
3. Mandell GA. Imaging evaluation of the neonate. In: Goodman LR, Putman CE, editors. Critical care imaging. 3rd ed. Philadelphia: W.B. Saunders, 1992:423-4.
4.Agrons GA, Harty MP. Lung disease in premature neonates: impace of new treatments and technologies. Semin Roentgenol 1998;33(2):101-16.