Conventional Radiography

Hydatid cysts present with a variety of radiologic patterns, but frequently cannot be recognized, let alone positively identified, by plain radiography. The presence of other calcified or partially calcified cysts elsewhere in the body may suggest the diagnosis. Unfortunately, calcification in cysts in the liver is seen in only 16% of patients who are known to have hydatid cysts in other parts of the body. Nevertheless, the appearance is so characteristic that the discovery of a smooth, well-defined, round, oval, or lobulated "tumor" anywhere in the body, especially if there is rim calcification, should suggest hydatid disease in any patient who is living in, has visited, or has emigrated from an endemic area.

Hydatid cysts may vary in diameter from 1 to 20 cm: there are often multiple cysts of different sizes in the same patient. Those in the liver (which is by far the most common site) often calcify (Figs. 3.41, 3.42, 3.43), as do those in other solid organs, e.g., the kidney and spleen. But calcification is extremely rare within lung hydatids and is not identifiable on plain radiographs within bone lesions or in most cerebral cysts.

Calcification of the cyst wall may have various patterns (Fig. 3.43). There may be a fine line of calcification that is well defined, usually sharp externally, but lacking clarity internally. Only part of the cyst wall may be calcified, giving a sickle-shaped or crescentic outline. Where the calcification is lacking altogether or is partial, inhomogeneous, or striped, there is the possibility of active growth: many believe this pattern is an indication for surgical removal of the cyst to prevent rupture, which could lead to biliary obstuction, disseminated hydatidosis or even death from anaphylaxis. If the cyst calcification is total, with a dense thick wall and calcified endocyst, the cyst is dead (Type III). Polycyclic calcification can be seen when both mother and daughter cysts have calcification within their walls; multiple daughter cysts are thought to indicate that the mother cyst's survival is threatened. A "crushed eggshell" or "sunburst" type of calcification may result from prior cyst rupture and collapse (Fig. 3.77B). The polycyclic and crushed eggshell types of calcification are virtually diagnostic of hydatid disease, but can rarely indicate the end result of a hematoma or mycotic infection.

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