Image Case : Hydatid Disease of the Liver

Hydatid Disease which is also referred to Echinococcosis or echinococcal disease, is a parasitic disease that affects both humans and other mammals, such as sheep, dogs, rodents and horses [1]. Hydatid disease remains a clinical problem worldwide, especially in areas where animal husbandry and subsistence farming form an integral part of community life [2]. The liver is the most commonly involved organ (52-77%) [3], but hydatid disease may affect any part of the body either as a primary or secondary event [2]. There are four forms of hydatid disease. Echinococcus granulosus (EG) is the most common and gives rise to cystic hydatid disease (CHD). Echinococcus multilocularis is uncommon and causes alveolar hydatid disease (AHD), which is far more aggressive and frequently mimics malignancy [4]. The rarest clinical form is Echinococcus vogeli or polycystic hydatid disease (PHD), with characteristics between CHD and AHD [5]. Echinococcus shiquicus, has been identified on the Tibetan plateau but to date no human infection has been described. CHD is a zoonosis infecting a variety of domestic and wild animals. There is no host specificity for the larval stage of EG, but the commonest intermediate hosts are sheep, cattle, buffalo, camels and pigs [6]. The developing hydatid cyst has three layers. The outer pericyst is composed of host fibroblasts, eosinophils, giant cells and modified hepatocytes. The middle laminated membrane is a cellular and impermeable to bacteria, and the innermost layer, the germinal layer or brood capsule, is translucent and is the origin of scolices and daughter cysts within the primary cyst [4]. The cyst usually contains crystalclear fluid which is strongly antigenic and may cause anaphylaxis if released into the circulation of the host. Most cysts remain silent when small and present only when complications such as rupture into the biliary tree, bacterial superinfection or free intra-abdominal rupture occur. Owing to the lack of symptoms in the early stages, the actual accurate assessment of the growth rate of these cysts is difficult [2].