3. Discussion
Echinococcus granulosus is a helminth parasite, dogs and other carnivorous animals are primary hosts and sheep are intermediate hosts, humans are usually infected as intermediate accidental hosts. which causes echinococcosis or HD. Humans usually become infected by ingesting food, milk, or water contaminated by dog feces containing the ova of the parasite1. The most common sites of hydatid cysts (HC) are the liver, and then are lungs2, only 0.5%–2% HD patients show a cardiac involvement3-7, possibly due to persistent movement and contraction of myocardium8. The distribution in different part of the heart depends on the coronary blood supply, the left ventricular wall is the most common cardiac location, followed by the right ventricle, pericardium, left atrium, and right atrium1,9,10. The interventricular septum (IVS) is less frequently involved, just reported in 4% of all cardiac cases2. However, in the majority cases of cardiac HC, the disease usually affects other organs simultaneously11, in other words, cardiac HC is more likely to happen secondary to hepatic HC, case like we reported here, HC located at the IVS without imaging findings of liver or lung involvement is extremely rare.
Most of HD patients can remain asymptomatic for many years, whereas, the condition seems different in patients with cardiac HC. S. Fennira and colleagues reviewed cases of HC in the IVS from 1964 to 2019, finally included 45 cases, showed only 5 patients (11%) were asymptomatic1. Yaman ND also reviewed studies of cardiac echinococcosis worldwide, which included 86 patients, only 5 patients (6%) were asymptomatic. These findings suggest cardiac HC is a more serious condition and easier to present clinical symptoms. The type and severity of clinical manifestations mainly depend on the organ involved, the number and size of the cyst and other complications12, thus, symptoms are various. Compression to coronary arteries by a cyst can cause myocardial ischemia, easily give rise to precordial pain, and more severe, it may cause myocardial infarction, which increase the incidence of sudden death. If the cyst gives the compression to the cardiac conduction system, conduction block will happen, if gives the compression to pulmonary artery, dyspnea and cyanosis may occur. When the cyst has a tendency of intracardiac development, direct mechanical interference to valves and changes to the size of chambers will influence the cardiac function, results in symptoms of heart failure, such as dyspnea, weakness, dizzy and edema. Complications including bacterial infection, cyst rupture and most serious, anaphylactic shock. However, exact prevalence remains unclear. This patient presented with intermittent chest pain, which suggested acute myocardial ischemia.
Some serological tests such as eosinophil count, indirect hemagglutin, enzyme-linked immune sorbent assay and Casoni intradermal test have clinical diagnosis value for Echinococcus granulosus infection, but due to the false negativity and limited sensitivity and specificity, are usually not enough to diagnose. The diagnosis is primarily confirmed by combination of clinical findings, imaging and serology. Eugenio Zalaquett and colleagues concluded features of HD on ultrasound, CT and MR imagings, and classified HC into five types to help clinical diagnosis12. Final diagnosis should be confirmed by histopathological examination, different developmental stage ofEchinococcus granulosus could be found. Aviral Gupta reported a case of cardiac HC, showed a pathological image of acellular lamellated membranes of HC with partially autolyzed brood capsules, which confirmed the diagnosis13. Similar HC in the background of myocardium could also be found on our pathological image.