Case 56.  Echinococcosis, multilocular (36 y-o F)
Surgical specimen of cystic liver lesions in a Hokkaido resident
Key words : 
Echinococcus multilocularis, liver cyst, Echinococcus granulosus    
Cysts are fused in the liver parenchyma. E. multilocularis is endemic in Hokkaido.   Lamellated cyst walls are hyalinized and collapsed (HE). Protoscolex is not observed in human cases.
The lamellated cyst wall is strongly PAS-positive. Identification of PAS-reactive lamellated material can be the clue for the histopathologic diagnosis of multilocular echinococcosis.   Reference case 56A
Lung metastasis of multilocular echinococcosis. Surgical specimen 10 years after hepatectomy for echinococcosis (HE). Multilocular cysts contain lamellated eosinophilic cyst walls. Metastatic lesions may also be seen in the brain, bone and kidney.
Liver lesion in a wild rat (Clethrionomys rufocanus bedfordiae) in Hokkaido
Invasive multilocular cysts in the liver contain numbers of protoscolex (HE, low power). Exogenous budding is characteristic of multilocular echinococcosis. Wild rats are the reservoir (intermediate host) of E. multilocularis.
  Liver lesion in a wild rat (Clethrionomys rufocanus bedfordiae) in Hokkaido
Protoscolex in the cyst (HE, high power). Hooklets and calcified spherules are histologically unique to the protoscolex. The final host of this small tapeworm (2 mm in length) is the fox and dog.
Reference case 56B
Echinococcus granulosus. Daughter cysts within a large unilocular cyst, surgically removed from a Peruvian Nisei. The patient died of anaphylactic shock during surgery. Leakage of the cyst fluid (hydatid fluid) should be avoided.
  Reference case 56B
Protoscolex in the daughter cyst (stereo microscopic observation). Hooklets on the rostellum are characteristic. In old cysts, isolated protoscolexes accumulate as hydatid sand.
Reference case 56B
Histologic features of the protoscolex and cyst wall of Echinococcosis granulosus (HE). The protoscolex contains a chain of hooklets. The cyst wall is not stained by H&E, except for the surface germinal layer.
  Reference case 56B
Lamellated structure of the cyst wall demonstrated by Grocott stain. The beautiful lamellated structure of the cyst wall is not recognized by H&E stain.