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The findings are presented of a macro and microscopic investigation of 89 hydatid hepatic cysts removed intact from 59 patients by total pericystectomy. Detailed analysis revealed significant morphostructural variability and cysts grouped into 10 types were characterized, providing useful clinical indications. Only 30 cysts resulted fertile (33.7%), probably due to mean age of sample; 7 of these were "classic" cysts, 1 "septated" and 22 "multivesicular" packed with daughter cysts (DC), of varying turgidity or collapsed. Among the remaining 59 sterile cysts, 52 were degenerated and classified as "hyperlaminated" cysts due to the presence of large convoluted sheets of laminar tissue (SLT) surrounded by varying amounts of caseous (40 specimens), granular (6) or gelatinous (6) matrix. Moreover, "multivesicular", "acephalocyst", "caseous" and "serous" cysts were also recovered among the sterile specimens. Some "multivesicular" cysts (14) appeared as "transitional forms" towards the various types of "hyperlaminated" cysts containing all different forms of DC and large SLT intermingled with a variously degenerated matrix. The comprehensive study allows to hypothesize the train of events leading, over the years, to the gradual transformation and degeneration of the larval form Echinococcus granulosus in the human liver.

The encysted larval form of Echinococcus granulosus may infest man as an incidental host. The liver is the organ most commonly involved, but the lung and brain may be affected. The disease is endemic where sheep are raised with dogs in a pastoral environment. Areas of high endemicity exist in rural North America. Human echinococcal disease is now seen in urban medical centers because of the changing patterns of migration and immigration. An echinococcal cyst of the liver is reported in a resident of the New York City metropolitan area. Details of the life cycle, pathology, diagnostic imaging techniques and surgical management of hydatid cysts are reviewed.