Daughter cysts, which are thought to develop from scolices, are produced either synchronously with matrix or they may appear first (Fig. 3.20). They are generally considered an abnormal part of the parasite's life cycle. Many investigators theorize that daughter cysts are formed only when there is a threat to the continued existence of the hydatid in the form of mechanical, chemical or bacterial insult. This may therefore be a defensive process of a damaged, degenerating, or dying cyst to guarantee survival. Even if the outer cyst is dead, daughter cysts may continue to survive and be infective, producing further daughter cysts, leading to the presence of multiple daughter and granddaughter cysts within a single unilocular hydatid cyst. The mother cyst and daughter cysts usually remain contained within the host-produced pericyst. Daughters replicate the structure of the mother cyst, but they do not stimulate production of their own pericyst as they are not in contact with host tissue. Cysts with a predominace of daughters are often erroneously thought to be septated (Fig.3.21), but the "septa" are in fact the opposing walls of daughter cysts flattened by contact with one another. When the daughters are removed, the "septa" disappear.

..

...

...

Fig. 3.20 The formation of daughter cysts in hydatid disease. Daughter cysts occur frequently in large, older unilocular cysts whose existence is threatened by some form of mechanical, chemical or bacterial insult. These daughter cysts are thin-walled balloons formed from the detached germinal layer of the mother cyst or from brood capsule cells. (A) A large, unilocular hydatid cyst of the liver containing numerous daughter cysts which lie free in the cyst fluid. In this fluid there is also hydatid sand, containing free scolices and hooklets. AFIP N-31977. (B) Multiple daughter cysts lying free within a large unilocular hydatid. (C) Numerous daughter cysts in E. granulosus infection involving the abdominal cavity of a monkey. (D) Multiple small cysts taken from the vertebral column of a patient with signs and symptoms of lower cord compression. (E) Cyst of E. granulosus showing the characteristic laminated and proliferative layers. The daughter cysts contain scolices, many of which have degenerated as evidenced by the presence of free hooks. (F) A daughter cyst lying free within the mother cyst and containing multiple invaginated scolices. The germinal epithelium and laminated, acellular ectocyst of the mother hydatid are on the left. AFIP 65-2463.

Fig. 3.21 CT scan of the liver showing a type II lesion with predominance of daughter cysts. The "septa" are the walls of daughter cysts flattened by contact with other daughters (Courtesy of Dr. Lewall and Clinical Radiology, 1998).