Abstract: Objective To investigate the formative mechanisms of the fibrous capsule around hepatic and splenic hydatid cyst. Methods HE stain was used to observe the histopathologic changes of the fibrous capsules around hepatic and splenic hydatid cysts and the adjacent parenchyma. The expression of collagen Ⅳ, fibronectin(FN), laminin(LN), transforming growth factor-β1 (TGF-β1) and tumor necrosis factor-α(TNF-α) were detected by using immunohistochemistry or in situ hybridization in fibrous capsules around 40 hepatic hydatid cysts and 15 splenic hydatid cysts including adjacent parenchyma. Results A special delaminated phenomenon was observed in the fibrous capsules around hepatic hydatid cysts. Granuloma-like pathologic changes were found in the fibrous capsules near worm and there were many depressed Glisson capsules and hepatic vein system in the fibrous capsules near hepatic parenchyma while these phenomena could not be observed in splenic hydatid cysts. All parameters were highly expressed in the fibrous capsules near hepatic parenchyma and the difference between the two fibrous capsules was significant(P<0.01). Conclusion The mechanisms of forming fibrous capsule around hepatic and splenic hydatid cysts are different. The fibrous capsule around hepatic hydatid cyst is a granuloma-like structure, covered by the pressed Glisson system and hepatic vein system with a small gap between them; while the fibrous capsule around splenic hydatid cyst is formed by granuloma-like tissue covering the worm and there is no gap between the capsule and the splenic parenchyma.

Key words: Echinococcus cyst, fibrous capsule, formative mechanism