Pathologic Quiz Case: Large Cardiac Mass in a 24-Year-Old Woman

A 24-year-old woman presented to an emergency department in the Middle East with a 3-day history of left-sided chest pain and dyspnea on exertion. She was 2 months postpartum and had experienced an uneventful pregnancy and delivery. She was found to be in acute distress on physical examination. Her blood pressure was 90/ 60 mm Hg. She was tachycardic (110 beats per minute), and her respiratory rate was 24 per minute. There was bilateral lower-leg pitting edema. A grade 2 systolic ejection murmur was heard over the aortic area. The chest radiograph showed cardiomegaly without pulmonary edema. Routine laboratory blood test results were within normal limits. Echocardiogram and computed tomography revealed (1) a solitary cystic filling defect in the left ventricle, with a circumferential opacified ring, measuring 4 × 4 cm (Figure 1); and (2) rupture of the left ventricular free wall. Computed tomography showed mild splenomegaly, with systemic embolic lesions noted in the spleen and upper pole of the right kidney. A cardiac neoplasm with tumor embolism was clinically suspected. The patient underwent emergency thoracotomy, with excision of the ventricular mass and repair of the ventricular rupture.The surgical specimen consisted of a deflated white cystic mass with a granular lining, measuring 6 × 7 cm in maximum dimensions. The cyst wall was gelatinous in consistency. Sections of the membranous portion revealed characteristic structures (protoscolices), with sickle-shaped hooklets (Figures 2 and 3). Sections from the adjacent myocardium showed a lymphocytic interstitial infiltrate without eosinophils.What is your diagnosis?Hydatid disease is caused by the adult tapeworm Echinococcus granulosus and less frequently by Echinococcus multilocularis. It is endemic in geographic regions with abundant grazing animals, such as South America, the Middle East, countries surrounding the Mediterranean, and Australasia. Carnivores, including household pets such as the dog, are usually the definitive host of E granulosus. Intermediate hosts, such as sheep and cattle, are usually herbivores. They acquire the infection by ingesting contaminated feces of a definitive host through grazing. This parasite is transmitted to humans through contact with an infected animal, usually by ingestion of food contaminated by intermediate host waste products through poor hygiene.After ingestion, the liberated “embryos” penetrate through the wall of the small intestine and enter the bloodstream. From there they are disseminated to various parts of the body where they anchor and develop into slow-growing cystic masses. No organ in the body is immune, but the liver is by far the most common organ affected (70% of all cases and principally affecting the right lobe), followed by the lung (25% of cases)1 and other sites. Cardiac echinococcosis is very rare indeed.2 Only 0.5% to 3% of all hydatid cysts are located in the heart. The parasite gains access to the heart from a primary infected organ via hematogenous spread to the coronary arteries, with subsequent transmural penetration, or by the rupture of pericardial hydatid cysts into the myocardium. The left ventricle is the most commonly affected site (75% of the cases),3 followed by the right ventricle and the interventricular septum. The clinical presentation of cardiac hydatid cyst depends largely on the site of involvement, the number and size of the cyst(s), and the age of the patients. Surprisingly, most cases are asymptomatic. Symptoms result from pressure effects of large cysts on the coronary circulation4 and the conducting system, or from the rupture of the hydatid cysts into the myocardium. The most frequent signs are chest pain and exertional dyspnea. Cough, palpitation, and arrhythmias have also been noted. Anaphylactic shock, congestive heart failure, and sudden death are noted among the serious or fatal outcomes reported.5 Because of the rarity of cardiac hydatid disease, this diagnosis is often missed at the time of presentation, even in regions of the world where hydatid disease remains endemic.As noted in our case, the embolic lesions were erroneously interpreted as embolic tumor implants, and the significance of the ring opacification of the cystic ventricular mass was overlooked. Otherwise, the pathology of cardiac hydatid disease is similar to that described in other involved organs. Grossly, the capsule of the hydatid cyst is white, gelatinous, and glistening, and the cavity is filled with liquid. Smaller daughter cysts are often seen within the dominant cyst. Microscopically, the hydatid cyst is composed of a hyalinized and laminated outer “cellular” layer and a characteristic nucleated “inner” germinative layer. The inner layer contains protoscolices with distinctive, refractile sickle-shaped hooklets. Demonstration of scolices or hooklets in hematoxylin-eosin–stained sections or Giemsa-stained smears of cystic fluid6 is diagnostic for hydatid disease. Hydatid hooklets are acid fast, and the Ziehl-Neelsen stain can enhance the presence of hooklets when screening cyst fluid.Peripheral eosinophilia is common, and tissue eosinophilia is often seen adjacent to the infection. In our case, only a heavy lymphocytic myocardial infiltrate was noted, and tissue eosinophilia was notably absent. Ultrasonography and computed tomography are most useful in the evaluation of hydatid cysts overall. Hydatid immunoelectrophoresis and enzyme-linked immunosorbent assay are additional diagnostic tools.7 Clinically, echocardiography remains the diagnostic method of choice for cardiac hydatid disease.34 Prompt diagnosis and surgical treatment are necessary to avoid complications.

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