Echinococcosis: Unexpected Occurrence and the Diagnostic Contribution of Routine Histopathology.

Echinococcus is the smallest of the major tapeworms. Humans are incidental hosts who become infected by exposure to soil contaminated with ova from the feces of the canine definitive hosts. The major species are E. granulosus (cystic echinococcosis) and E. multilocularis (alveolar or sylvatic echinococcosis), both common worldwide but unusual and not reportable in the United States. Human disease is characterized by slowly growing visceral cystic masses often containing daughter cysts and hydatid sand. In nonendemic areas, the clinical evaluation includes imaging, serology, and surgery; metastatic tumor is a major consideration. The diagnosis depends on the morphologic recognition of scolices and hooklets, albeit degenerated, within the cyst or attached to the cyst wall. Highly suggestive cyst wall features are an acellular hyaline lining surrounded by focally calcific fibrous tissue and chronic inflammation. We report 7 patients encountered in the Chicago area (5 E. granulosus, 2 E. multilocularis) who presented with cystic masses affecting the liver, lung, soft tissue, and spleen. The initial diagnosis was established or suggested by intraoperative evaluation of cyst fluid or cyst wall histopathology. Organism parts were found in 5 cases; 1 patient had a hyalinized cyst wall with a positive IgG (enzyme-linked immunosorbent assay), and 1 had a positive Western blot and a 30-year history of treatment. Treatment included cyst resection, hepatic lobectomy, intraoperative cyst injection, and benzimidazole therapy. There was 1 death. In a nonendemic area, the awareness of the pathologist to the possibility of this disease will exclude a neoplasm and facilitate prompt antihelminthic treatment.