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A 67-year-old female presented to her primary care physician with right upper quadrant pain. She had a history of frequent foreign travel, including a number of countries in South America and Asia. Imaging demonstrated a 12.5-cm hepatic cyst. The cyst was drained and subsequent examination of the fluid indicated no infectious or malignant etiology. Serology tests for Entamoeba histolytica (amebiasis) and Echinococcus (hydatid disease) antibodies were negative. The patient underwent additional hepatic cyst aspirations for recurring symptoms over a number of years. Approximately four years later, imaging demonstrated cyst enlargement and some more solid internal components within the cyst. Repeat Echinococcus antibodies ordered were elevated. Cyst aspiration stained with the Ryan modified trichrome stain demonstrated the images seen below.


  1. What parasitic infections should be considered in the diagnosis?

  2. Do the images shown above provide a diagnosis?

  3. Is her travel history relevant? Why or why not?

  4. Why didn’t the original cyst drainage demonstrate parasitic elements?

(Scroll Down for Answers and Discussion)


The images presented in Diagnostic Quiz #80 are the following: ANSWERS TO QUESTIONS:

  1. Based on the images seen above, the presumptive diagnosis would be hydatid disease with Echinococcus granulosus; hooklets from disintegrated protoscolices are visible, as is one protoscolex.

  2. Currently, four species are recognized within the genus Echinococcus: E. granulosus (which causes cystic disease), E. multilocularis (which causes alveolar disease), E. vogeli (which causes polycystic disease), and E. oligarthrus (which causes polycystic disease). The areas of the world involved in sheep and cattle raising tend to be the areas where infections with

    E. granulosus are endemic; they even include the Basque sheep farmers in California.

  3. The number of infections in both animals and humans has decreased over the years as a result of education and various control measures. However, in some areas in Central Asia, figures suggest the surgical incidence is now greater than 10/100,000 (up to 27/100,000 in Tajikistan), and many of the cases are in children and the unemployed. Her travel history is certainly relevant. The risk of infection depends to a high degree on the association

    between humans and dogs, with the exception of the lion strain. Those at high risk include populations where dogs are used to herd sheep and are also intimate members of the family, often having unrestricted access to the house and family members. Cystic echinococcosis has been recorded in 21 of China's 31 provinces, autonomous regions, and municipalities (approximately 87% of the territory). This infection constitutes one of the major health problems in this part of the world. Hydatid disease caused by E. granulosus is a zoonosis of major public health concern throughout Latin America, particularly in the Andean and South Cone regions. Cystic echinococcosis is also widely found throughout the region comprising Arab North Africa and the Middle East.

  4. Various daughter cysts (brood capsules) bud off from the inner germinal layer and may remain attached or float free in the interior of the fluid filled cyst. The individual scolices bud off from the inner wall of the daughter cysts; these protoscolices and free daughter cysts are called hydatid sand. Each scolex will normally invaginate to protect the hooklets. Although not every cyst will produce daughter cysts and/or scolices, this general tissue organization is called a unilocular cyst, in which the cyst contents are held within a single limiting cyst wall. In an early infection, hooklets and/or intact protoscolices may not be visible. There are multiple studies in the published literature that reflect large variability in the sensitivity and specificity of serologic tests, including additional variability between laboratories. Also, 10% to 20% of patients with hepatic cysts do not produce detectable specific serum antibodies (IgG) and thus give false-negative results.


Hydatid disease in humans is potentially dangerous; however, cyst size and organ location will greatly influence the outcome. Clinical symptoms may appear after an incubation period of several months to years. Hydatid cysts should be considered in patients with abdominal masses with no clearly defined diagnosis. Although eosinophilia is present in 20 to 25% of patients, it is merely suggestive. Many asymptomatic cysts are first discovered after radiologic studies. The cyst will usually have a well-defined margin with occasional fluid level markings. These studies can also be helpful in diagnosing osseous involvement. Scans may also demonstrate a space occupying lesion, particularly in the liver. If the cyst is large and located in the abdomen, a thrill is sometimes detected.


Once the cyst is discovered and surgical removal is selected as the approach, some of the cyst fluid can be aspirated and submitted for microscopic examination to detect the presence of hydatid sand, thus confirming the diagnosis. Hydatid sand is not always present. Also, if the cyst is old, the daughter cysts and/or protoscolices may have disintegrated, so that only the hooklets are left. These may be difficult to find and identify if there is debris within the cyst. Cyst aspirates to be evaluated for hydatid “sand” (daughter cysts, protoscolices, hooklets) can be examined as wet direct mounts after centrifugation. Several stains can be used to visualize the hooklets; one of the best is the Ryan trichrome blue modified trichrome stain for the microsporidia. The stained smears can be examined using routine microscopy with transmitted light.


The hooklets and/or protoscolex hooklets stain purple using the Ryan Modified Trichrome stain (normally used for microsporidian spores). The overall intensity of the stain color will vary, depending on the destain step, the staining time, and the thickness of the smear. An unstained smear of hydatid sand protoscolices can be seen below. Using the Ryan modified trichrome stain, the dark hooklets would stain pink/purple.


Garcia, L.S. 2016. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, D.C.


Each Quiz has a two section format: the first section will present the Quiz topic and the second section will provide a discussion of the answer and/or various options in response to the Quiz situation presented to the user. In some situations, there may be more than one correct response.

The content within this site is made possible through the extensive contribution of Lynne S. Garcia, M.S., MT(ASCP), CLS(NCA), BLM(AAB), F(AAM), Director, Consultantation and Training Services (Diagnostic Medical Parasitology and Health Care Administration). For additional information, she can be contacted at LynneGarcia2@verizon.net.

Reference: Garcia, L.S. 2015. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, D.C.

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