Question
35-year-old male came to the surgery out-patient department with vague abdominal discomfort and intermittent pain in the right upper quadrant for the past four months. On examination, there is mild tenderness in the right upper quadrant and hepatomegaly. Ultrasound examination of the abdomen revealed a large, well defined cystic lesion in the right lobe of the liver. The patient has no significant history in the past. He has a fondness for stray dogs in his neighborhood.
- (a) What is the probable diagnosis. 1 mark(s)
- (b) Describe the life cycle of the etiological agent and name the intermediate host in the life cycle 4 mark(s)
- (c) Name two organs other than liver where these cysts can occur 1 mark(s)
- (d) Describe the treatment options for this patient e) Add a note on prevention of this infection 2 mark(s)
Answer
(a) Probable diagnosis: Hepatic hydatid disease (cystic echinococcosis) — a well-defined cystic liver lesion, chronic right-upper-quadrant discomfort, hepatomegaly, and a history of close contact with stray dogs (the definitive host) is the classical presentation.
(b) Life cycle and intermediate host: Echinococcus granulosus has a two-host life cycle — dogs (and other canids) are the definitive host, harbouring the small adult tapeworm in their intestine and shedding eggs in their faeces; sheep (and other livestock) serve as the natural intermediate host, ingesting eggs from contaminated pasture, with resulting larvae forming hydatid cysts in their organs — the cycle completes when a dog eats infected offal from a slaughtered/dead sheep. Humans become infected accidentally by ingesting eggs from food/water contaminated with dog faeces, or, most commonly, via hand-to-mouth contact after handling an infected dog (as in this patient’s fondness for stray dogs) — functioning as a dead-end intermediate host, since human hydatid cysts are never consumed by a dog. Ingested eggs hatch in the small intestine, releasing oncospheres that penetrate the gut wall and travel via the portal circulation to the liver (the commonest site, acting as the first capillary filter), where the larva develops into a hydatid cyst with a laminated layer, germinal layer (producing protoscolices and daughter cysts), and a host-derived pericyst.
(c) Two other organs where cysts can occur: the lungs (the second most common site, for larvae bypassing the liver’s filtering capillary bed) and, less commonly, the spleen, kidney, brain, or bone.
(d) Treatment options:
- Watchful waiting for small, inactive/calcified cysts.
- Albendazole (a prolonged course, often months) for smaller active cysts, or as peri-procedural cover before/after PAIR or surgery.
- PAIR (Puncture-Aspiration-Injection-Reaspiration) — a minimally invasive, image-guided technique: the cyst is punctured, fluid aspirated, a scolicidal agent (hypertonic saline or ethanol) injected to kill remaining germinal material, and reaspirated — combined with albendazole cover.
- Surgery (cyst removal, ideally without intraoperative rupture) for large, complicated, or anatomically difficult cysts, or those unsuitable for PAIR. (Percutaneous aspiration purely for diagnostic purposes is generally avoided, given the risk of anaphylaxis from antigenic cyst fluid and secondary dissemination of viable germinal material.)
(e) Prevention: deworming of dogs in endemic pastoral areas (interrupting the definitive-host side of the cycle), proper disposal of infected animal offal rather than feeding it to dogs, hand hygiene after contact with dogs, and health education in communities with close human-dog-livestock contact.