Cardiac hydatid cyst is a parasitic disease seen rarely in India. It is caused by infection with larvae of echinococcus granulosus. In the life cycle of echinococcus humans are the accidental hosts, dogs or other carnivores are the primary host and sheep as intermediate host. Humans get infected by eating food or fluids contaminated with dog feces containing ova of the echinococcus.
The most common site of the hydatidosis in humans is liver (50–70%), followed by lungs (5 to 30%), muscles (5%), bone (3%), kidneys (2%), spleen (1%), and brain (1%) . Cardiac hydatid is uncommon occurring in less than 2% of cases . Left ventricular free wall is the most common location followed by right ventricle, pericardium, left atrium, and right atrium. Interventricular septum is a rare location and occurs in less than 4% of cardiac hydatid cases . Larvae reach the myocardium through systemic or pulmonary circulation or as a direct extension from other adjacent organs.
Clinical presentation depends on the location of the cysts, whether they are intact and infiltration of the underlying structures. Only few patients especially those with large size and involving underlying structures present with symptoms  like dyspnea, palpitations, angina, conduction disturbances, arrhythmias, valvular dysfunction, and outflow tract obstruction [3,4,5]. They can also present as systemic or pulmonary embolization . Rupture of the cyst is a fatal complication resulting in anaphylactic shock, embolization, pericardial tamponade, and mortality in 75% of the patients. Very rarely, rupture may be silent. The cause for dyspnea and increase in pulmonary pressures in this patient was due to extensive involvement of lung due to pulmonary embolization.
Diagnosis is usually made by echocardiography and many times is sufficient . Typical echocardiographic appearance includes well defined cystic mass with or without septations . Echocardiography demonstrates the location of the cyst, its number and the relation with the surrounding structures, any valvular dysfunction, or outflow tract obstruction or pericardial effusion. In an echocardiography description study of 14 patients by Hamda et al., 8 patients had single cystic mass and 5 patients had multiple cysts . A solid lesion can also be seen in some cases of infection with echinococcus multilocularis . The differential diagnosis for a cystic mass on interventricular septum includes cardiac tumors, cysts, metastasis, IVS aneurysm, etc.
Further modalities like CT and CMR are very important in detailed characterization of the cyst, to assess the relation of the cyst with surrounding cardiac or extracardiac structures and helps in planning the surgery. The appearance of hydatid cyst on CMR is characteristic with hypointense on T1-weighted and hyperintense on T2-weighted. More specific signs include calcification and presence of daughter cysts . CMR could identify additional cysts not identified by echocardiography . Very few cases have been reported with nuclear imaging. There are no characteristic patterns on FDG PET for hydatid cyst and usually have peripheral calcification and minimal FDG uptake. However, very high uptake can mimic malignancy [10, 11]. In the present case, CMR was done to find out the nature of the cyst, its activity, and its relationship with the surrounding structures. With the use of CMR in our case, we could identify that the cyst is causing interference of contractility with hypokinesia of the septum, confirmation of decrease in EF, and also decreased perfusion in the septum was noted raising the possibility of infiltration of the underlying septum. The natural history of hydatid cyst is that the cyst grows slowly between the cardiac fibers and remain active for many years until it becomes large enough to cause compression, invasion of the surrounding structures .
Treatment involves combined medical and surgical therapy. Medical therapy includes albendazole which helps in preoperative sterilization of the cyst and decreases intraoperative dissemination. It is preferable to continue post-operative albendazole as it helps in reduction of recurrences .
Because of poor prognosis in case of rupture and only partially effective medical therapy, preferably all cases of cardiac hydatid cyst should undergo surgical excision. Surgical techniques depend on the location of the cyst and most often done under cardiopulmonary bypass. One of the problems during surgery is the extreme fragility of the cystic wall and risk of dissemination into systemic circulation. To prevent this, before enucleation an anti-helminthic solution (like 2% formalin, 0.5% silver nitrate solution, 20% hypertonic saline solution, 1% iodine solution, or 5% cetrimonium bromide solution) is to be injected in to the cyst .
In our case, as the patient was running fever despite multiple antibiotics and anti-parasitic therapy, we have done PET which showed no uptake in the cardiac hydatid cyst. We went ahead with surgery in this patient even though PET showed less FDG uptake as the cyst was affecting left ventricular contractility and because of the risk of rupture. This case highlights the poor prognosis of cardiac hydatid cysts, associated complications, and underlines the importance of early recognition and surgical management in such patients.