Snapshot A 55-year-old woman comes to the emergency department complaining of abdominal pain. She states that she has suffered intermittent nausea for 2 years. Then 3 months ago she began to notice right-sided abdominal pain. She denies vomiting, diarrhea, or constipation. She has not been to a doctor in 3 years since she moved from Peru. She has had no surgeries. She takes no medications. On physical examination, there is moderate right upper quadrant tenderness. An ultrasound shows a 5-cm cyst in the right upper lobe of the liver with an irregular, calcified wall. Introduction Clinical definition liver cyst caused by Echinococcus tapeworm Epidemiology Demographics most common form is E. granulosus and E. multilocularis usually acquired during childhood but do not manifest symptoms until adulthood Risk factors geographic South America, Middle East, sub-Saharan Africa, and western China close contacts with dogs and sheep ETIOLOGY Pathogenesis definitive host usually dogs intermediate hosts include sheep, goats, camels, horses, cattle, and swine transmission adult tapeworm inhabits small intestine produces eggs that are expelled in stool eggs ingested by incidental host (fecal-oral transmission) parasites hatch from eggs and penetrate intestinal mucosa to enter blood/lymphatic system migrates to liver or other organs to form hydatid cysts humans are incidental hosts Presentation Symptoms mostly asymptomatic if liver involved 2/3 of the time nausea, vomiting, and right upper quadrant pain if lung involved 25% of the time cough, chest pain, dyspnea, and hemoptysis Physical exam hepatosplenomegaly imaging Ultrasound best initial test inexpensive 90-95% sensitive single anechoic, smooth, and round cyst may have septations may have a thick or irregular wall “eggshell” appearance if calcified may have daughter cysts (peripherally based cyst within a cyst) Computed tomography or magnetic resonance imaging 95-100% sensitivity for greater anatomic detail to establish location and number of cysts, presence of ruptured or calcified cysts, and to guide management better for evaluation of extrahepatic cysts Studies Diagnostic testing studies complete blood count login to view 2 more bullets serologic and antigen assays login to view 3 more bullets cyst aspiration/biopsy login to view 2 more bullets Differential Simple cyst distinguishing factors thinner wall, no calcifications, no septations, and no daughter cysts sterile fluid if aspirated negative serology login to view 1 more bullet Cystadenoma or cystadenocarcinoma distinguishing factors rapid growth tumor cells on histopathology login to view 2 more bullets may have elevated levels of carcinoembryonic antigen (CEA) negative serology Treatment First-line albendazole indication login to view 1 more bullet mechanism of action login to view 1 more bullet adverse effects login to view 4 more bullets Second-line image-guided percutaneous drainage indication login to view 2 more bullets adverse effect login to view 2 more bullets Third-line resection indication login to view 3 more bullets adverse effect login to view 1 more bullet Other treatments Mebendazole and praziquantel are less effective Complications Mass effect Budd-Chiari syndrome portal hypertension cholestasis cirrhosis Secondary bacterial infection Cyst rupture presentation fever acute hypersensitivity reaction (i.e., anaphylaxis) obstructive jaundice death