Persistent interstitial pulmonary emphysema-like cyst associated with metastatic synovial sarcoma.

Interstitial pulmonary emphysema is characterized by the presence of gas dissecting the interstitial tissues of the lung. Clinically, it may be acute or persistent, and the latter can be further categorized as localized or diffuse. Usually, it appears in preterm neonates with a history of assisted ventilation or respiratory distress. Although far from frequent, the localized variety of persistent interstitial pulmonary emphysema (PIPE) can develop spontaneously in full-term babies or infants without any obvious underlying pulmonary disease. Histologically, PIPE is characterized by the presence of uni- and multinucleated histiocytes lining the inner surface of the cysts. In this report, we describe a 15-year-old male with synovial sarcoma (SS) of the right ankle diagnosed 4 years previously who developed pulmonary metastasis, one of which presented cystic changes with features of PIPE.