Meta-echinococcal arthrosynovitis: a clinical, anatomical and pathological entity not previously recognised.

The authors describe a case of echinococcosis of the tibia which occurred twice in seven years, the first time with signs of active involvement of the knee joint. Certain special aspects of articular echinococcosis, not up to now reported in the literature, are dealt with. The conclusion reached is that in an articular site the parasite can give rise either to a veritable "echinococcal" arthritis or, as in the case presented, to a the synovial affection which cannot be defined as "echinococcal" because the synovium did not contain living larval forms of the parasite, but only microscopic chitinous inclusions, arising from the disintegration of sterile hydatids, which had escaped from the adjacent bony focus into the joint. The synovium reached to their presence with an intense inflammatory response of a predominantly histiocytic nature. The term "meta-echinococcal arthrosynovitis" is suggested as a more accurate designation of this syndrome.