Primary cardiac hydatid disease: cross-sectional imaging features.

ABSTRACT

Background. Although hydatid disease is common, individual series are usually not large as far as primary cardiac hydatid disease is concerned. We believe this study is the largest series of primary cardiac hydatid disease for which cross-sectional imaging is available.

Methods. We reviewed the radiologic and medical records of 9 pathologically proven cases of primary cardiac hydatid disease. Echocardiography, computed tomography (CT), and magnetic resonance imaging (MRI) were used. In 5 patients, all three modalities were used, and in 4 only CT was available.

Results. Three types of cardiac involvement (pericardial, left ventricular, and right atrial wall) were detected. The cysts showed daughter cyst formation, detached parasitic membrane, rupture, segmental calcification, and end-stage calcification.

Conclusion. Echocardiography is useful in detecting the cystic nature. Computed tomography best shows the wall calcification. Magnetic resonance imaging depicts the exact anatomic location and nature of the internal and external structures and is the modality of posttreatment follow-up.

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HYDATID DISEASE is a parasitic infestation caused by the larvae of the tapeworm Echinococcus. Echinococcus granulosus is the species that most commonly infects humans. The infestation is prevalent in most parts of the world, especially in sheep farming and cattle farming areas of Asia, North and East Africa, South America, Australia, and the Middle East. The parasite requires two hosts in its life cycle--a definitive host (usually a dog) and an intermediate host (humans). Humans are infected by direct contact with an infected dog or by ingestion of contaminated food. Echinococcal embryos migrate through the intestinal mucosa, enter intestinal venules and lymphatics, and arrive in the liver in 60% to 70% of cases. (1-4) If embryos bypass the liver, they reach the systemic circulation and are carried by the bloodstream to any organ or any tissue in the body. Cardiac involvement is rare, with a reported occurrence between 0.5% and 2.0% of all hydatid disease. (2-5) Cardiac hydatidosis may present a clear picture , or it may become a life-threatening condition and a clinical puzzle. (6) Although cardiologists and cardiothoracic surgeons deal with cardiac hydatid disease, they cannot always make the diagnosis on the basis of chest x-ray films and clinical examination alone but must sometimes rely on other radiologic examinations as well. In this study, the radiologic features of 9 cases of hydatid disease of primary cardiac involvement are reported. We believe this is the largest series of patients with primary cardiac hydatid disease for which cross-sectional imaging is available.

MATERIALS AND METHODS

We retrospectively reviewed the radiologic findings and medical records of 9 pathologically proven cases of cardiac hydatid disease seen at our institution from January 1995 through December 2000. The 5 female and 4 male patients ranged in age from 18 to 63 years, with an average age of 44.4 years.

Echocardiography, CT, and MRI were the radiologic modalities used in this study. In 5 patients, all three modalities were used, and in 4 only CT was available. Computed tomography was done with Somatom Plus S (Siemens, Erlangen, Germany), using a 10 mm slice thickness at 10 mm intervals from the manubrium sterni to the upper pole of the kidneys. Images were obtained with and without intravenous contrast material (Iopamiro 300, Bracco, Italy; Ultravist 300, Schering, Germany). Intravenous contrast material (1.5 mL/kg) was introduced as a bolus (rate, 1.5 mL/sec). Magnetic resonance imaging was done on 1.0 arid 1.5 T scanners (Siemens, Erlangen, Germany) with ECG-triggered short TR/TE, long TR/TE conventional pulse sequences in three planes. Contrast enhanced images were not obtained. Echocardiography was one with an ATL 3000 HDI (Bothell, Wash) Doppler unit. On radiologic examinations, we evaluated the number, size, location, morphologic appearance, and contrast enhancement pattern of lesions, as well as the p resence or absence of calcification, calcification pattern (segmental or ring-like), and pericardial effusion. The imaging findings were retrospectively analyzed by two radiologists (S.K. and O.K.), and decisions were made by consensus. All patients were treated surgically. Radiologic diagnosis was confirmed by pathology.

RESULTS

Patient characteristics are summarized in the Table. Hydatid disease involved the pericardium in 5 patients, the left ventricle in 3, and right atrial wall in 1. The smallest lesion was 2 cm, and the largest was 10 cm. Most of the cysts ranged from 5 to 7 cm. All the cysts were unilocular, with no detectable septations. Pericardial lesions in one of the patients were multiple (Fig 1) and ruptured in another patient, who had massive pericardial effusion with tamponade formation (Fig 2).

The hydatid cysts showed various stages of development and degeneration. These consisted of daughter cyst formation (n = 3), detached parasitic membrane (n = 1), rupture (n = 1), segmental calcification (n = 3), and end-stage calcified cyst (n = 1).

On CT, the cysts were seen as hypodense, well-defined cystic masses (Fig 3). In 1 case (pericardial), peripheral dense and complete ring calcification of the cyst was detected, representing the death of the cyst. In 3 cases, cysts showed segmental calcification (2 pericardial, 1 right atrial) (Fig 4). After contrast injection, all the lesions showed peripheral ring-like enhancement. On echocardiography, the lesions were seen as hypoechoic cystic masses with posterior wall enhancement (Fig 5). On MRI, simple cysts appeared hypointense on T1-weighted images and hyperintense on T2-weighted images (Fig 1). On T2-weighted images, four of the lesions showed peripheral ring-like hypointensity representing pericystic host reaction. Daughter cysts were seen as smaller cystic masses heavily hyperintense within the mother cyst (Fig 6). Detached membrane was visualized as the separation of the inner membrane that floats in the lumen of the cyst and was hypointense. None of the patients had hepatic or mediastinal-pulmonar y hydatid diseases.

DISCUSSION

Cardiac involvement in hydatid disease is either primary or secondary. Primary involvement of the heart usually occurs via coronary arteries. Secondary involvement of the heart occurs from hydatid disease of adjacent organs, such as lungs and parts of the mediastinum, or from the dome of the liver in which abdominal cysts prolapse through the diaphragm. (1,2) The left ventricle is affected most often (50% to 70%), followed by right ventricle, pericardium (15% to 25%), and interventricular septum (5% to 15%). (1-3,8-10)

Symptoms, signs, and potential complications depend on the location of the cysts. (2) In the early period, cysts grow slowly between cardiac fibers without causing any symptoms. As the cysts reach a reasonable size, fever, palpitations, arrhythmias, and heart failure can occur. Cysts located in the interventricular septum may cause serious conduction defects and intermittent valvular block, which may give rise to syncope and sudden death. One of the major complications is tamponade caused by rupture of the cyst into the pericardium, which occurred in one case in this study (patient No. 2). Other fatal complications due to cardiac hydatid cyst are cardiac arrest, myocardial infarction, and aneurysm of the left ventricular wall. (2,3,8) Therefore, early and prompt diagnosis is crucial for avoiding these complications.

In the radiologic diagnosis of cardiac hydatid disease, echocardiography, CT, and MRI might be used. Echocardiography shows the cystic nature of the mass. It also may define the internal septa. Intraoperative use of echocardiography helps in making the diagnosis and in planning the management of cysts. (7) However, echocardiography is operator-dependent, has a limited field of view (especially of lesions located behind the sternum), and may fail to indicate whether the lesion is pericardial or myocardial. (11,12) Also, echocardiography cannot be used to differentiate hydatid cysts from congenital pericardial lesions. Computed tomography and especially MRI are superior to echocardiography for the evalution of masses and their relationship to surrounding tissues. Coexisting pulmonary or mediastinal hydatid disease may also be detected by CT and MRI. Calcifications are best seen on CT. (2,6,8) Detecting small calcifications may be important in providing a clue for the diagnosis of hydatid cyst. Therefore, noncon trast CT should be done before contrast-enhanced imaging. Localized and/or segmental calcifications may occur when the parasite is still alive. (2,6,9) On the other hand, calcification of the cyst itself indicates the death of the cyst. (4) Infected cysts may appear on CT as poorly defined masses, in contrast to the more clearly defined masses seen in uncomplicated cases. (6)

With the advent of the cardiac gated fast sequences, MRI has become the method of choice in evaluating many diseases of the heart. (2) Its multiplanar demonstration of the hydatid lesion offers the surgeon the exact anatomic location as well as the size of the lesion and its relationship to adjacent structures, such as heart chambers and valves. (2,6,10,13)

On MRI, hydatid cyst is usually characterized by a spherical lesion that is hypointense on T1-weighted images and hyperintense on T2. On T2-weighted images, the periphery of the cyst may disclose a hypointense rim, which represents the pericyst consisting of fibrous reactive capsule. (2,3,6,14) After contrast administration, ring enhancement may be detected. (15) Septations and daughter cysts can be precisely evaluated. Daughter cysts are seen as cystic structures that are attached to the germinal layer and are hypointense relative to the cystic fluid on T1 and hyperintense on T2. Collapsed parasytic membranes appear on MRI as twisted linear structures within the cyst. (6) Complex cysts may be visualized as a long TE, approaching the appearance of solid tissue. Magnetic resonance imaging is also superior in showing the irregularities in the rim. Loculated and even small pericardial effusions are easily detected. (2) On follow-up, MRI is highly effective in the evalution of postoperative residual lesions and i n early discovery of recurrent lesions. (2,11)

In the differential diagnosis of cardiac hydatid disease, other cystic masses such as myocardial aneurysms, pericardial cysts, pleuropericardial cysts, or constrictive pericarditis with calcification should be considered. Although pericardial cysts are rare, pleuropenicardial cysts are not uncommon. Both are typically situated at the cardiophrenic angle. Cross-sectional imaging allows exact localization of the lesion and shows the morphologic appearance, which helps in differentiating these lesions from hydatid disease. In constrictive pericarditis, calcification and thickening without a cystic mass may be present in the pericardium. To diagnose constrictive pericarditis, both CT and MRI provide additional information on the status of vena cava, atria, ventricles, and pleural changes. (16) Myocardial aneurysms, especially those containing mural thrombi and calcification, may resemble calcified hydatid disease on echocardiography. Because myocardial aneurysms have characteristic appearances on CT and MRI, they can easily be differentiated from hydatid cyst.

To conclude, in cardiac hydatid disease, echocardiography is especially useful for the detection of the cystic nature of the lesion. Computed tomography best shows the wall calcification and may provide the differential diagnosis of calcified cardiac-pericardiac masses; MRJ depicts the exact anatomic location of the cyst and the nature of both internal and external structures. It also detects even small pericardial effusions and should be the radiologic method of choice for detection of noncalcified lesions and for posttreatment follow-up.

TABLE

Characteristics of Patients With Cardiac Hydatid Disease

Patient           Location  Detached  Daughter             Segmental
  No.    Age/Sex  of Cysts  Membrane    Cyst    Rupture  Calcification

   1      18/F       LV        +         +         -           -
   2      59/M       P         -         +         +           -
   3      63/M       RA        -         -         -           +
   4      44/F       P         -         -         -           -
   5      34/M       P         -         -         -           +
   6      54/F       P         -         -         -           +
   7      40/F       LV        -         -         -           -
   8      38/F       LV        -         +         -           -
   9      50/F       P         -         -         -           -

Patient      Ring           No.          Size
  No.    Calcification  of Lesion(s)     (cm)

   1           -           Single       10 x 10
   2           -           Single     10.0 x 8.5
   3           -           Single      7.5 x 6.0
   4           +           Single        7 x 6
   5           -           Multiple   2-6
   6           -           Single      4.5 x 3.5
   7           -           Single      6.0 x 5.5
   8           -           Single        3 x 3
   9           -           Single        2 x 2

LV = Left ventricle, P = pericardium, RA = right atrium.

References

(1.) Beggs I: The radiology of hydatid disease, AJR 1985; 145:639-648

(2.) Von Sinner WN: CT and MRI findings of cardiac echinococcosis. Eur Radiol 1995; 5:66-73

(3.) Cantoni 5, Frola C, Gatto R, et al: Hydatid cysts of the inter ventricular septum of the heart. AJR 1993; 161:753-754

(4.) Lewall DB: Hydatid disease: biology, pathology, imaging and classification. Clin Rodiol 1998; 53:863-874

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(6.) Pedrosa I, Saiz A, Arrazola J, et al: Hydatid disease: radiologic and pathologic features and complications. Radio graphics 2000; 20:795-817

(7.) Birincioglu CL, Bardakci H, Kucuker SA, et al: A clinical dilemma: cardiac and pericardiac echinococcosis. Ann Thorac Surg 1999; 68:1290-1294

(8.) Von Sinner WN: Radiographic, CT and MRI spectrum of hydatid disease of the chest: a pictorial essay. Eur Radiol 1993; 3:62-70

(9.) Desnos M, Brochet E, Christofini P, et al: Polyvisceral echinococcosis with cardiac involvement imaged by two dimensional echocardiography, computed tomography and nuclear magnetic resonance imaging. Am J Cordial 1987; 59:383-384

(10.) Manisali M, Ozaksoy D, Kovanlikaya I: The role of MR imaging in cardiac echinococcosis. AJR 1997; 168:282-283

(11.) Limacher MC, McEntee CW, Attar M, et at: Cardiac echinococcal cyst: diagnosis by two-dimensional echocardiography. J Am Call Cordial 1983; 2:574-577

(12.) Gouliamos A, Anderou J, Steriotis J, et at: Detection of pericardial heart disease by computed tomography. Clin Radial 1984; 35:397-400

(13.) Kotolas GE, Magoufs GL, Gouliamos AD, et al: Evaluation of hydatid disease of the heart with magnetic resonance imaging. Cardiovase Intervent Radial 1996; 19:187-189

(14.) Alper H, Yunten N, Sener RN: Intramural hydatid cysts of pulmonary arteries. Eur Radiol 1995; 5:666-668

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(16.) Ovchinnikov VI: Computerized tomography of pericardial disease. Vestn Rentgenol Radial 1996; 1:10-15

RELATED ARTICLE: KEY POINTS

* Primary cardiac involvement is a rare manifestation of hydatid disease, which may either present a clear picture or become a life-threatening condition.

* Radiologic examination plays a major role in the differential diagnosis in which other cystic masses should be considered.

* Echocardiography is useful for the detection of the cystic nature of the lesion.

* Computed tomography shows the wall calcification and provides the differential diagnosis of calcified cardiac pericardiac masses.

* Magnetic resonance imaging depicts the exact anatomic location of the cyst and the nature of the internal and external structures.

From the Department of Radiology, Istanbul University, Cerrahpasa Medical Faculty, and the Clinic of Cardiothoracic Surgery, Siyami Ersek Cardiovascular Surgery Hospital, Istanbul, Turkey.

Reprint requests to Sebuh Kurugoglu, MD, Istanbul University, Cerrahpasa Medical Faculty, Department of Radiology, 34300 Istanbul, Turkey.