Hydatid cyst — DTM&H MCQ

Correct answer: D — Ultrasound staging with echinococcal serology

The correct answer is D, ultrasound staging with echinococcal serology. The clinical picture (Moroccan shepherd, dog and sheep contact, incidental hepatic cyst with daughter cysts, afebrile) is classic for cystic echinococcosis (hydatid disease) caused by Echinococcus granulosus, and daughter cysts within a mother cyst are a defining sonographic feature of this diagnosis. Cysts can be incidentally discovered by radiography, and specific antibodies are detected by serological tests that can support the diagnosis; ultrasound also allows WHO-IWGE staging (CE1 to CE5), which determines whether watchful waiting, drug therapy, PAIR (puncture, aspiration, injection, re-aspiration) or surgery is appropriate. This combined imaging plus serology approach is non-invasive, safe and directly guides stage-specific management, making it the single best investigation. Why the other options are wrong: B. Blood film: This detects blood parasites such as malaria or filariae and has no role in diagnosing a cystic liver lesion; there is no fever or travel history suggesting a blood-borne parasitaemia here. C. Urine microscopy: This is used for conditions such as schistosomiasis or urinary tract pathology, not for hepatic cystic disease; it gives no information on the liver cyst. E. Widal serology: This tests for antibodies to Salmonella Typhi/Paratyphi in suspected enteric fever, which is irrelevant to an afebrile patient with an incidental liver cyst. A. Blind cyst aspiration: Unguided puncture of a suspected hydatid cyst is dangerous because spillage of protoscolices can cause anaphylaxis or peritoneal seeding (secondary echinococcosis); aspiration should only follow confirmed diagnosis and staging, and even then be done as a controlled PAIR procedure with anti-helminthic cover, not blindly. Key point: Daughter cysts on ultrasound in a patient with livestock/dog exposure should prompt WHO-IWGE ultrasound staging plus echinococcal serology, never blind aspiration, because unguided puncture risks cyst rupture and anaphylaxis.

Reference: WHO Fact Sheet: Echinococcosis (2024), Diagnosis section, https://www.who.int/news-room/fact-sheets/detail/echinococcosis; WHO-IWGE ultrasound classification of cystic echinococcosis as applied in UK DTM&H and tropical medicine practice