Clinical History
35-year-old Middle Eastern man with right upper quadrant mass and pain. Elevated GGT and ALP.
Imaging Findings
Sonographic examination of the liver revealed a number of cysts with variable features. The largest measured 13 x 9 x 11 cm, was situated in the left lobe, and had simple features: anechoic and thin-walled. Two cysts in the right lobe of liver were more complex with internal curvilinear structures in the cyst lumen. The abdominal aorta, kidneys, spleen, gallbladder, and biliary system appeared normal on ultrasound.
CT with contrast of the abdomen and pelvis confirmed hepatic cysts. Some appeared simple, with thick walls, while 2 had an internal curvilinear membrane-like structure within the cyst lumen.
Discussion
Echinococcosis, or hydatid disease, is the formation of hydatid cysts as a result of Echinococcus granulosus infestation. This tapeworm is common in areas of Asia, North Africa, and South America [1], but it is rare in the developed world, where most cases are imported [3]. The definitive host is the dog [1], in whose faeces eggs are shed [2], contaminating its fur [4]. Through contact with the animal or its faeces, intermediate hosts, such as sheep or humans, acquire the eggs, which then hatch in the duodenum [1]. They penetrate the small intestinal mucosa and migrate via the portal vein to the liver, where more than half of cysts are found [2]. They next most commonly occur in the lungs (25%), followed by the brain, kidneys, and bones [1].
Clinically, hydatid disease remains asymptomatic for many years [5]. When symptoms do present, they usually result from rupture, mass effect, allergic reaction, or secondary infection [4]. Hepatic cysts typically present with abdominal pain and hepatomegaly, and occasionally obstructive jaundice and reduced appetite, about 5-20 years after onset [4].
Ultrasound is an important tool for diagnosis (sensitivity 93-98%), staging, and follow-up [5], while CT (sensitivity 90-97%) confirms the diagnosis [4]. In its earliest phase, characterised by simple cysts, hydatid disease may be indistinguishable from other cystic pathologies on imaging [2]. Evolution through a series of discrete stages is its hallmark; the World Health Organisation has classified and described them in detail [7]. The cysts begin as simple structures with echogenic walls and anechoic contents [7]. Over time, the walls thicken, and daughter cysts appear as multiloculated honeycombs inside the original cyst [2]. As the inner membrane separates from the outer, a split wall appearance emerges, progressing to a "water lily" sign once the membrane has completely collapsed and floats inside the cyst [2]. Further cyst degeneration results in a filling of the cyst with echogenic contents and calcification of its walls.
Treatment options include various surgical procedures [6], antiparasite chemotherapy with agents like albendazole, and monitoring [5]. Cyst size and stage determined on imaging affect what is feasible [5]. The prognosis depends on the organs affected but is generally good [8].
Once symptoms present, echinococcal infestation will likely have been active for many years, and the cyst(s) will have progressed beyond the simple stage. Ultrasound is a good tool to identify and stage hepatic hydatid cysts and allows for visualisation of their most characteristic features.
Differential Diagnosis List
Hydatid cysts
Haemorrhagic cysts
Hydatid cysts
Cystic metastases
Abscesses
