Simple liver cysts and cystoid lesions in hepatic alveolar echinococcosis: a retrospective cohort study with Hounsfield analysis

Background. Alveolar echinococcosis (AE) is a rare zoonosis caused by the larval stage of the tapeworm Echinococcus multilocularis. AE lesions affect the liver in more than 98% of cases. AE lesions have various morphological characteristics that are described in the Echinococcus multilocularis Ulm classification for computed tomography (EMUC-CT). One of these characteristics is a cystoid portion. The aim of the study was to compare the density of simple hepatic cysts with cystoid portions of AE lesions classified on the basis of the EMUC-CT. Results. Hounsfield Unit (HU) measurements of the cystoid portions of all EMUC-CT type I–IV AE lesions (n = 155) gave a mean of 21.8 ± 17.6, which was significantly different from that of 2.9 ± 4.5 for the simple hepatic cysts (p < 0.0001). The difference between each of the individual AE types and simple hepatic cysts was also significant. In addition, the HU values of the cystoid portions in types I, II and IIIa/b and simple cysts were each significantly different from type IV (p < 0.0001). The HU measurements in type IV presented by far the highest mean. Conclusions. The significantly higher density measured in the cystoid portions of hepatic AE lesions offers a good means of differentiation from simple hepatic cysts