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The child was taken to the operating room and underwent a left lateral thoracotomy. The pleural cavity contained yellowish gelatinous matter. The parietal and visceral pleura were thickened, and the left lung was completely collapsed and displaced superiorly and medially. A bronchopleural fistula in the left lower lobe was actively discharging air. After decortication and resection of the inflamed parietal pleura, the lung was re-expanded and the fistula hole in the lower lobe was widened, thereby exposing a cavity. The cavity contained typical remnants of a pulmonary hydatid cyst capsule as well as multiple bronchial fistulas. As the disease had destroyed most of the lobe parenchyma, a left lower lobectomy was performed. Histopathological examination revealed typical structures of an Echinococcus granulosuscyst with calcified scolices indicative of an aged cyst (Figure 3).

Hydatid lung cysts are caused by the larva of the tapeworm, E granulosus,which is endemic to Africa, the Middle East, Latin America, the southwestern United States, and southern Europe.¹The adult E granulosustapeworm uses its scolex (head containing hooklets) to attach itself to the intestinal mucosa of its definitive host, the dog, and sheds eggs into the dog's stool. Intermediate hosts, namely livestock, become infected while grazing on contaminated soil, leading to the release of embryos into the duodenum. The embryos then travel into the portal circulation, where they complete the life cycle of the tapeworm and develop into cystic metacestodes.^1- 2Humans may become intermediate hosts by ingesting the worm's eggs from contaminated water or soil or from contact with infected dogs. In this case, the child most likely became infected from his pet dog or from one of the numerous neighborhood dogs.

Infected individuals are always asymptomatic after primary infection and may become symptomatic if a cyst ruptures or from cyst mass effect. The typical incubation period ranges from months to years.³Hydatid cysts typically occur in the liver (70%) and lung (20%), though the kidney, spleen, peritoneal cavity, skin, muscle, heart, vertebrae, and ovaries are occasionally affected.^3- 4This child initially had chest pain due to pleural irritation from the large cyst and after its rupture had severe respiratory distress necessitating immediate surgical intervention.

Definitive diagnosis of cystic echinococcosis or hydatid disease is accomplished using imaging, including computed axial tomography. Serologic diagnosis may be helpful initially and for follow-up after surgical or medical treatment of the cyst. Enzyme-linked immunosorbent assay, indirect hemagglutination or immunofluorescence assay, radioallergosorbent testing, and latex fixation are sensitive but nonspecific methods of diagnosing echinococcosis. The immunoassays are compromised by the cross-reactivity of other helminths.^1,3

Surgical resection is the mainstay of therapy for lung cysts, in particular for large cysts compressing vital organs. Medical therapy with albendazole is beneficial; however, there is no uniform recommendation for duration of therapy. Percutaneous cyst puncture has been reported to cause anaphylactic reactions in a minority of cases. The relapse rate after removal of a lung cyst is 11.3%.⁴Complications such as tension pneumothorax, pleural perforation, and bronchial perforation are rarely associated with echinococcal lung cysts.

The differential diagnosis of the child's initial presentation includes community-acquired pneumonia, lung abscess; cavitary tuberculosis; and less commonly, a cystic tumor. The radiological finding of a liver cyst on abdominal computed tomography together with the presence of an encapsulated structure in the lung prompted consideration of echinococcus. The child was discharged with a prescription for a 3-month course of albendazole and with plans for an elective liver cystectomy.

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Correspondence:Andrew P. Steenhoff, MBBCh, Abramson Research Center, The Children's Hospital of Philadelphia, 3615 Civic Center Blvd, Ste 1202, Philadelphia, PA 19104-4318 (steenhoff@email.chop.edu).

Accepted for Publication:March 9, 2010.

Author Contributions:Study concept and design: Ludmir, Kuskov, Mubaiwa, and Steenhoff Acquisition of data: Valliante, Kayembe, Mubaiwa, and Steenhoff. Analysis and interpretation of data: Ludmir and Steenhoff. Drafting of the manuscript: Ludmir, Kuskov, Mubaiwa, and Steenhoff. Critical revision of the manuscript for important intellectual content: Ludmir, Valliante, Kayembe, and Steenhoff. Administrative, technical, and material support: Ludmir, Valliante, Kuskov, Kayembe, and Mubaiwa. Study supervision: Steenhoff.

Financial Disclosure:None reported.