A 46-year-old male from Mauritania, West Africa, was referred to the pulmonary clinic for an abnormal screening chest radiograph obtained at the tuberculosis clinic. The patient had been in the United States for 6 years and recently completed a course of isoniazid for latent tuberculosis. He denied all symptoms except back pain on history and review of systems. No medical history was reported, and his surgical history was noncontributory. The patient had a 5 pack-year history of smoking but quit 20 years prior. The patient visited Mauritania 3 years ago but otherwise denied travel or sick contacts. Physical examination demonstrated normal vital signs and blood oxygen saturation. Findings from cardiac, pulmonary, and abdominal examinations were unremarkable.
The frontal chest radiograph revealed a large oval masslike density in the right mid to lower lung (Fig. 1). Computed tomography (CT) of the chest demonstrated a large fluid-filled cystic mass in the right lung, abutting the major and minor fissures, which contained a daughter cyst in its posteromedial aspect (Fig. 2). Abdomen CT additionally showed a septated cystic lesion in the inferior tip of the right hepatic lobe (Fig. 3). Laboratory data including complete blood count, basic metabolic panel, liver function tests, coagulation profile, and echinococcal IgG and IgM were all within reference range. Results of pulmonary function tests were also normal.
The patient was referred to thoracic surgery to be evaluated for resection of the right lung cystic lesion with preoperative and postoperative treatment of albendazole (400 mg twice daily for 3 cycles of 28 days on and 14 days off the drug). Operative treatment was chosen, including cystotomy and capitonnage. Under general anesthesia with lung isolation via a double-lumen endotracheal tube, a right (serratus-sparing) posterolateral thoracotomy was performed in the fifth intercostal space. A white cystic structure was identified in the right middle lobe (Fig. 4). Spillage of cyst contents was meticulously avoided. Povidone iodine-soaked sponges were packed around the cyst. It was needle aspirated to decrease intracystic pressure. The cyst was then opened (cystotomy), the remaining fluid was aspirated, the germinative membrane was removed, and the cavity was irrigated with povidone iodine. Bronchial openings were oversewn, and the residual cavity was obliterated with imbricating sutures (capitonnage). He was discharged on the fifth postoperative day.
The cyst, cyst fluid, and pericyst tissue were submitted for histopathologic analysis. Gross examination of the collapsed cyst showed white areas intermixed with semitransparent membranes (Fig. 5A). The cyst and surrounding pericyst tissue showed three distinct morphological layers. The outer pericyst layer was composed of fibrous and granulation tissue with the adjacent lung parenchyma showing a chronic inflammatory infiltrate containing prominent eosinophils (Fig. 5B). The second layer was composed of a laminated, acellular substance (Fig. 5C) and corresponded to the white areas apparent on gross examination. The inner third layer was represented by the semitransparent membranes and consisted of a single cell layer with budding larvae (protoscolices) arising singly and in bunches (Figs. 5C and D). The cyst fluid was clear and contained numerous protoscolices. Some of the protoscolices were arranged in clusters with an associated single cell membrane identical to that forming the inner layer of the cyst (Fig. 5E). Wet mount preparations of the fluid showed numerous protoscolices with 2 rows of hooklets (Fig. 5F). Detached hooklets were also present in the cyst fluid.
Echinococcosis with pulmonary hydatid disease.
Hydatid disease is a parasitic infection caused by the larval form of the tapeworm Echinococcus. It manifests in 2 main forms, which include the unilocular cystic form caused by Echinococcus granulosus and the multilocular alveolar form caused by Echinococcus multilocularis.1 The unilocular form is much more common and is depicted in this case.
Endemic to some regions of the world, including South America, North Africa, Asia, and Australia, hydatid disease affects humans and animals.2 Most cases of echinococcosis in the United States occur in immigrants from endemic areas. Dogs and other canines are the definitive hosts, whereas other warm-blooded vertebrates, usually grazing animals such as sheep, cattle, goats, horses, pigs, and camels, serve as intermediate hosts. Humans may become intermediate hosts by contacting a definitive host or ingesting contaminated water or vegetables.
The adult worm inhabits the small intestine of the definitive host and produces eggs that pass through the host's feces. The intermediate host ingests the eggs, which are digested and broken down by gastroenteric enzymes. Larvae are released, invade the intestinal mucosa, and enter the portal circulation where they are filtered by the liver. There they can gain access to the systemic venous circulation and subsequently the lung. The larvae can then develop into fluid-filled cysts, which consist of 3 layers. The outer layer, or pericyst, is made of fibrous and granulation tissue that represents the host tissue reaction to the cyst. The fibrous tissue varies in thickness, depending on the age and organ where the cyst is located. The middle layer is an acellular laminated membrane produced by the parasite. The inner layer is the germinal membrane from which the protoscolices grow. The protoscolices differentiate in bunches called brood capsules, which break into the hydatid fluid and continue to grow to form secondary or daughter cysts. The cyst fluid contains numerous protoscolices and brood capsules in suspension referred to as hydatid sand. The cyst is fertile if brood capsules are present and sterile if brood capsules are absent. The protoscolices have 2 rows of hooklets. The hooklets, even if detached, are diagnostic and often the only recognizable structure found in degenerated cysts. The protoscolices are infective and can form cysts in the intermediate host or mature into an adult worm if ingested by a definitive host.1,3,4
The lungs are the second most common site of E. granulosus infection in adults after the liver. In children, pulmonary infection is most common.5 Uncomplicated pulmonary hydatid disease, which is most often asymptomatic, typically manifests on chest radiographs and CT as well circumscribed homogenous round or oval masses that measure near-water density. The cysts can be solitary or multiple and measure up to 20 cm in diameter. Depending on their location, some cysts can change shape to conform to adjacent structures, such as bronchi, pleura, other cysts, and the mediastinum. Displacement of surrounding structures is reportedly uncommon. Cyst calcification is also rare. The appearance of simple closed cysts can be altered by superimposed infection, hemorrhage, and infarction. Furthermore, the sharp margination of the cyst can be lost because of atelectasis and reactive change in the surrounding lung parenchyma. In some circumstances, these changes can simulate pneumonia or neoplasm.4-6
Symptoms from pulmonary hydatid disease are more often associated with cyst rupture, which can lead to release of antigenic material and subsequent immunologic reactions. Acute hypersensitivity reactions may include fever, urticaria, wheezing, and even life-threatening anaphylaxis.3 The release of hydatid fluid can result in allergic pneumonitis, secondary bacterial pneumonitis, or bronchopneumonia.
Should an enlarging cyst erode into a bronchiole, air is introduced between the pericyst and laminated membrane, appearing as a thin lucency termed the crescent or meniscus sign. This signifies impending cyst rupture and is an indication for urgent thoracotomy. An open or ruptured cyst has a variety of possible radiographic manifestations. When the cyst ruptures and air enters the endocyst, an air-fluid level forms in the endocyst, capped by the air crescent. This is termed Cumbo's or double-arch sign. As the endocyst collapses, it floats dependently within the pericyst cavity, resulting in the water lily or Camalote sign. A daughter cyst rarely forms, appearing as a circular density in the dependent portion of the cavity.4-6
Infection of the pericyst cavity has an appearance similar to a pyogenic lung abscess, including thick wall, air-fluid level, and surrounding pneumonia. Rupture of the cyst with complete emptying of its contents can infrequently produce a gas-filled cyst resembling a pneumatocele or bulla. In rare cases, the cyst ruptures into the pleural space, leading to hydropneumothorax and empyema.4,5
Hydatid disease can manifest in less common intrathoracic sites as well. Other intrapulmonary locations include endobronchial cysts and pulmonary artery emboli usually from rupture of right-sided cardiac or hepatic cysts. In addition to the heart, intrathoracic extrapulmonary cysts can involve the pleura, mediastinum, chest wall, and diaphragm.2
Our case illustrates an uncomplicated pulmonary cyst, which was found incidentally on a screening chest radiograph. Given the characteristic daughter cyst demonstrated by CT, the clinical diagnosis of pulmonary hydatid disease could be confidently suggested. Pathological analysis confirmed the diagnosis by demonstrating numerous protoscolices and the characteristic morphology of a hydatid cyst.
The authors thank Bernie Lenshitz, MD, for his assistance in the care of this patient.