Cysts and pericysts in the lung virtually never calcify for unknown reasons. Cysts in other sites, including the liver, spleen, kidney, mesentery, mediastinum and pericardium, may calcify. Calcification of the pericyst, which can develop at all stages of the life cycle of hydatids, is found in nearly one-third of liver cysts (Fig. 3.12). Pericyst calcification does not always indicate that the cyst is dead, but calcification of the endocyst does (Fig. 3.13). Lesions in the spleen (Fig.3.14) and kidney (Fig. 3.15) usually have a structure similar to those in the liver.

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Fig. 3.13 (A) CT scan through true pelvis showing a Type III hydatid. This was judged to be dead as the endocyst of both the daughter and mother are calcified and the lesion has an irregular, nonspherical outline. Intraperitoneal hydatids evoke very little pericystic reaction because they do not compress host tissue as they do in the liver. Thus, the peripheral calcification in this lesion is mainly endocystic, not pericystic. The indirect hemagglutination test for hydatid was negative and the lesion was not removed. In time it will probably become smaller and more densely calcified, to resemble the lesion in: (B) Type III lesions are not normally resected, but as this one protruded beyond the liver edge it abraded the peritoneum as the patient breathed, causing pain. Left: external surface. Right: cut surface showing calcified matrix. Note the calcified laminated membranes (arrows). The remaining matrix which is composed of older, more degenerated, and heavily calcified membranes no longer has any discernible structure. The lesion was stony hard and had to be cut with a saw. (Courtesy of Dr. Lewall and Clinical Radiology, 1998 ).