History of present illness:
The patient is a 48 year old female with no significant past medical history who was in her usual state of health until about 10-14 days prior to admission at which time she was noted to have shortness of breath and chest pain episodes. She described the pains as sharp pain lasting a few seconds and going away by itself. Review of systems revealed paroxysmal nocturnal dyspnea as well.
The patient was admitted to hospital and underwent echocardiography for clinical suspicion of cardiac syndrome which revealed a suspect mass in the right ventricular septum. For further evaluation, cardiac MR imaging was performed which revealed a 3 cm right ventricular mass with nonspecific features for which differential considerations included a myxoma. On third day of admission the patient was taken to the operating room for excisional biopsy. The procedure consisted of surgical excision of right ventricular mass on cardiopulmonary bypass with arrest of the heart, cryoablation of right ventricular muscle, and epicardial scan of the aorta. The surgical specimens were sent to the department of pathology for evaluation which revealed the presence of echinococcus granularis.
The etiology of echinococcosis involves ingestion of animal feces (usually dog) containing the eggs of the echinococcus parasite. The parasites can then travel to any area of the body and encyst themselves. Cardiac involvement is considered to be very rare, with most cases of hydatid disease disseminating to the bones or liver. Presentation of hydatid disease typically is dependent upon which area of the body has been seeded. For example, development of a hydatid cyst in the liver may result in abdominal pain. Dissemination of the bones may result in deep, aching bone pain. In our case, the patient developed cardiac symptoms due to involvement of the interventricular septum. A key consideration during the diagnostic process is to NOT biopsy or aspirate the lesion if hydatid cyst is considered – anaphylaxis may result. Regarding regional distribution, hydatid disease is most common in South America, the Middle East, Central America, Africa and less commonly may be seen in the Southwestern United States. For confirmation, a serologic ELISA AgB (antigen B-rich fraction) might be considered.
The gross pathologic features include a fluid-filled cyst, usually round, containing multiple daughter cysts. The cysts tend to be the color of pearl when viewed grossly. The histologic features include a hyaline-laminated wall and an inner germinal layer studded with developing brood capsules consisting of protoscolices formed within brood capsules.
The pathology report revealed minute fragments of myocardium associated with laminated eosinophilic debris showing the presence of cholesterol crystal clefts and dystrophic calcifications. Mature lymphoplasmacytic inflammatory infiltrate and foreign body-type giant cell were seen. Immunohistochemistry was positive for PAS and AFB.
For a larger view, please click Hydatid 2
Figure 2: Histology of 3 cm mass excised from the interventricular septum with AFB stain.
The imaging characteristics vary depending on modality, with MRI considered the study of choice. Hydatid disease in the chest may present as multiple round masses with well-defined borders. These can be of variable size from 1 cm to greater than 20 cm in diameter. Because they are blood-borne, they can be multiple in 30% of cases.
On non-enhanced CT scan, they are typically round in shape with thin walls and a density similar to that of water. They do not typically calcify. On contrast-enhanced CT, there may be moderate enhancement of the cyst wall. The radiologist should consider the possibility of multiplicity in all cases and evaluate the mediastinum, heart, chest wall, pulmonary artery and diaphragm for involvement.
On MRI, hydatid cysts typically show fluid signal on T1 sequences with internal multiseptated or multicystic components. If the cyst has degenerated, it may become isointense to muscle. On T2-weighted sequences, they also follow fluid signal. Degenerated cysts will become lower in signal intensity on T2-weighted sequences. Enhancement pattern is variable on T1 contrast-enhanced images.
Ultrasound has no role in the evaluation of echinococcal disease of the chest aside from the limited use of echocardiography to look for cardiac involvement.
For a larger image, click Hydatid 3
Figure 3: MRI of the heart revealed a right ventricle mass in the interventricular septum with nonspecific imaging characteristics. Differential considerations would include myxoma, metastatic malignancy, vegetation, other primary cardiac tumor such as sarcoma, lymphoma, among other possibilities.
In this case, from an imaging standpoint the findings were nonspecific, so a differential diagnosis was provided in the radiology report. For a mass in the right ventricle localized to the interventricular septum, differential considerations would include a cardiac myxoma (most commonly would occur in the left atrium), metastatic deposit (e.g. sarcomatous mass, colorectal, renal, lung or leiomyoma), intracardiac angiosarcoma or other primary cardiac tumor, vegetation from infective endocarditis or rhabdomyosarcoma.
Albendazole or mebendazole orally administered would be an appropriate treatment for an asymptomatic patient with a definitive diagnosis. However, in the presence of cardiac symptoms and lack of definite diagnosis, surgical resection/excisional biopsy is more appropriate.
The prognosis of this disease is generally favorable. The patient responded well to surgery with resolution of cardiac symptoms. The patient was subsequently placed on anti-helminthic drugs and made a full recovery.
Which organism is responsible for hydatid disease?
A. Echinococcus granularis
B. S. aureus
C. S. pneumonia
D. C. perfringens
|Visit our Case of the Month Archives||Next Page >|