There are basically three types of hydatid cysts which can be recognized on intravenous or retrograde urography (Fig. 3.79). Closed hydatids (type I) have an intact cyst lining and adventitia and do not communicate with the renal collecting system. The outline of the kidney may be enlarged, with a rounded mass (with or without calcification) causing elongation and splaying of the infundibula and calyces and, occasionally, obliteration of one or more calyces from pressure. These cysts, especially if not calcified, may be impossible to differentiate from other renal masses by pyelography, urography, or angiography as already noted. Nephrotomography may show a thick cyst wall with an inhomogeneous lucent center.

With the pseudoclosed or exposed type of hydatid cyst, contrast media can interpose itself in crescent-like fashion in the space between the laminated ectocyst and the pericyst, producing the "goblet" or "wine-glass" sign (Surraco's sign) (Fig. 3.79 ).

When the cyst has ruptured and is communicating with the renal collecting system, contrast medium from either an intravenous or retrograde urogram can spread around the cyst or fill it (Fig. 3.78C): there is usually a residual "neck" where the communication exists. In other patients, there may be a renal cavity, indistinguishable from renal abscess, tuberculosis, or papillary necrosis. In this open type of hydatid cyst, an intermittent or permanent communication exists between the hydatid and the pyelocalyceal system so that contrast medium flows directly into the cyst. Usually there is a typical mottled appearance of contrast, insinuating itself among a mass of daughter cysts but, occasionally, if the cyst contents are tightly packed, the contrast will be compressed between the contents and cyst wall to produce an extensive false crescent sign.