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Hydatid disease, a serious health problem, is endemic in many sheep and cattle raising areas. Though many kinds of medicines were used experimentally, operation is the only effective treatment for thoracic hydatidosis. The surgical treatments of 1230 patients with the disease in our division between June 1957 and December 2002 are discussed below.
CLINICAL DATA
Patients
Of the 1230 patients, mean age 35.2 years (range, 2 to 69 years), 764 patients were men and 466 were women. There were 913 patients less than 40 years old. Of these patients, 879 (71.5%) lived in rural areas and 233 (18.9%) were less than 14 years old. The symptoms were cough in 678 (55.1%) cases, haemoptysis in 353 (28.7%), chest pain in 567 (46.1%), sputum in 380 (30.9%), and asymptomatic in 142 (11.5%). The number of cases showing no sign in physical examination was 455 (37%), however 418 (33.9%) cases had dullness on percussion of the chest, 372 (30.2%) cases had weak breath sounds on auscultation of the chest and 364 (29.8%) had enlargement of the liver.
The locations of hydatid cysts are shown in Table 1 . Hydatid cysts are more frequently located in the right lung than the left and lower lobe than upper. Cases with liver dome cysts numbered 168 (13.6%), with cysts in the chest cavity 78 (6.3%), in the mediastinum 10 (0.8%), in chest wall 8 (0.7%), in myocardium and pericardium 4 (0.3%), and 3 (0.2%) in diaphragm.
Ultrasonography was performed on 1103 cases and the diagnostic rate was 89.1%. Casoni's test was performed on 1021 cases and the positive rate was 87.9% (897); 911 cases had indirect Coomb's test and the positive rate was 86.6% (798) and 692 cases had positive result for the immuno-electrophoresis test (75.9%).
Treatment
Treatment regimes of these 1230 cases are shown in Table 2.
Outcomes
One thousand two hundred and eighty nine operations were performed and 1225 cases were cured; 5 patients died (all before 1980). A few cases recurred (41, 3.3%), and most of them had a contamination of the chest cavity or operative area during their first operation.
DISCUSSION
Echinococcosis infection in humans is a zoonotic disease caused by larval cestode and is endemic in stock raising areas in northwest China. In cystic echinococcosis, caused by echinococcus granu-losus, the liver is the first and the most frequently involved organ, followed by the lung. Hydatid cyst can lodge in the lungs, pleural cavity, mediastinum, chest wall, diaphragm, liver dome or myocardium and pericardium.
A hydatid takes about half a year from larvae's lodging into human body to the formation of a 1 to 2 cm cyst. A hydatid cyst is composed of a parasite, the endocyst, surrounded by a pericystic layer, the exocyst, which is a fibrous layer due to host reaction. The exocyst is a fluid filled, elastic, white, elastic hyaline, cyst and is easily dissectible from the pericyst because there is only slight adhesion between them. The exocyst, which is functionally a protective layer against the cyst, consists of compressed lung tissue of the host with its associated inflammatory reaction and fibrosis. There is no air between the endocyst and the exocyst because leakage into pericyst is obstructed by the endocyst. The negative pressure of pleural cavity facilitates a hydatid cyst growing into the peripheral area of the lung. For a large cyst, at least a part of it may emerge on the surface of the lung.
Pulmonary hydatid cysts result from cyst rupture or infection and may be solitary, multiple, simple or complicated. In this series, solitary cysts and the simple type were more common than the multiple and complicated types. Pulmonary hydatid cysts can form in any pulmonary lobe but a lower lobe is more common, particularly those of the right lung. In our series, the percentages of the cyst locations were 60.3% in the right lung, 39.7% in the left, 50.0% in the lower lobe, and 31.5% in the upper, which probably related to the difference of blood flow between bilateral lungs and the anatomical feature of the lower lobe.
Intact or simple thoracic hydatid cysts may remain asymptomatic for a long time. As they enlarge, some may show symptoms such as slight chest pain, nonproductive cough and dyspnoea resulting from compression of adjacent organs. Rupture of the hydatid cyst into an adjacent bronchus may occur because of vigorous coughing and expec-toration of a large amount of salty sputum consisting of mucus, hydatid fluid and occasionally fragments of the cystic membrane. The scolices can be found by microscopy in the sputum. When rupture of the hydatid cyst occurs into the pleural space, hydro-pneumothorax develops, followed by empyema.
The diagnosis of simple thoracic hydatid cyst is not difficult and can be made according to: 1) a history of continuous contact with dogs or cats in endemic areas; 2) round or oval, solitary or multiple, sharp edged homogeneous densities revealed by chest radiography; 3) cystic lesion confirmed by ultrasonography; 4) immunodiagnosis such as Casoni's intradermal test and indirect haema-gglutination. In our series, the Cansoni's reaction was positive in 87.9% of cases and indirect haemagglutination in 86.6%. The serological reagent for diagnosis of hydatidosis was reported to be a fast, simple and reliable method, the positive rate of which was 89.5% in 170 cases.［1］ Ruptured or infected thoracic hydatid cysts, i.e., compli-cated, should be differentiated from pneumonia, lung abscess, tuberculosis, lung cancer and empyema by computed tomography, magnetic resonance imaging (MRI) and bronchoscopy when necessary.［2,3］
The principles of mandatory surgical intervention［4］ are evacuation of the cyst with removal of the endocyst, avoidance of contamination and mana-gement of the residual cavity. Normal lung tissue must be preserved as much as possible in the operation.［5］ The most commonly used surgical techniques are: 1) Needle aspiration of the cyst in situ, which can be applied to central and ruptured or infected cysts. In patients with a central cyst less than 3 cm in diameter, after sucking out the cystic content, cystectomy and removal of cyst membrane must be performed under needle guidance, otherwise, the complete removal of endocyst would be more difficult. In two of our cases, the endocyst was not found. 2) Excision of entire peripheral cysts larger than 3 cm in diameter by enucleation. Careful dissection must be used to prevent cyst rupture, which would lead to intraoperative contamination and postoperative recurrence. When the exocyst is opened, bronchial openings are closed first and then the cavity is obliterated by means of purse-string sutures along the bronchus. When the cystic cavity opens downward, the residual cavity need not be obliterated if bronchial openings are closed and pericystic lung tissues have good expansion and no air leak. In 12 of this group, the cavity was left open and good results were observed. It should be noted that distorted ligation of bronchus, incomplete haemostasis and closure of residual cavity are risk factors for infection and abscess formation. Because of the risk of rupture for enucleation, segmentectomy or lobectomy should be performed for those peripheral cysts less than 2.5 cm in diameter. For patients with pulmonary hydatid cysts, especially those located on the right side, one should keep in mind that a liver cyst must be searched for with ultrasonography or computed tomography to strive for single operation for pulmonary and liver dome cysts.［6］ For cysts with abscesses or severe pulmonary destruction, segmentectomy, lobectomy or even pneumonectomy are required.［7］ If hydatid cyst is concomitant with empyema, pleural drainage must be performed in the stageⅠ.［8,9］ If the lung cannot expand, decorticationor thoracoplasty is required. For patients with hepatobronchial fistula caused by the rupture of liver dome cysts to lungs, peritoneal cavity drainage without thoracotomy should be performed under ultrasonographical guidance. Both needle aspiration and enucleation have good results in treating thoracic hydatid cysts,［10］ and the latter showed the lower recurrent rate. In addition, liquid nitrogen freezing technique was also employed in treating hydatid cyst in selected patients, ［11］ which has the advantage of en bloc resection, conservation of lung parenchyma as much as possible, prevention of hypersensitive shock and suffocation and avoidance of recurrence. For cysts less than 3 cm in diameter and located in the peripheral lung, pleural cavity or mediastinum, wedge resection or needle aspiration was also be performed by. Because of the risk of hypersensitive reaction, asphyxia and recurrence caused by cyst rupture, huge thoracic cysts are a contraindication of video assisted thoracoscopic surgery.
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