Extension of the disease can usually be well evaluated. MRI provides sophisticated differentiation between soft tissue structures such as the myocardium, endocardium and pericardium (Figs. 3.110, 3.111, 3.112, 3.113, 3.114, 3.115), but artifacts and signal dropout may limit MR imaging. Previous heart surgery such as valve replacement, pacemaker insertion or other metallic implants are contraindications for MRI. Nevertheless, in the absence of these limitations, it is the method of choice for multiple follow-up examinations to look for residual hydatidosis, or early recurrence, and to assess the effectiveness of long-term chemotherapy in inoperable patients.

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Fig. 3.112 Intracardiac hydatid cyst in a Saudi Arabian patient. (A) T1-weighted MR image (SE 750/30) shows a low-intensity mass in right atrium in close contact with tricuspid valve (arrow). (B) A second MR image (SE 1000/50) reveals a high-signal- intensity mass, suggesting the cystic nature of the lesion. (Courtesy of Dr. von Sinner and AJR, 1991).

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Fig. 3.113 A 30-year-old woman with hydatid cysts of the pericardium, left ventricle and right atrium in close contact with the tricuspid valve, mitral valve and left atrium. (A) ECG-gated MRI, transaxial view (0.5 T, SE 750/ 30 ms). Observe the large left pericardial "ringed" hydatid cyst (HC) consisting of homogeneous cyst contents surrounded by a low-intensity ring thought to be due to the ectocyst of the parasite and pericyst of the host (arrows). (B) ECG-gated MRI, transaxial view (0.5 T, SE 1000/150 ms), showing low-intensity partition of several cysts more clearly (arrows). (C) ECG-gated MRI, transaxial right anterior oblique view (0.5 T, SE 1000/ 50 ms), showing the heart in systole with the right atrial cyst demonstrating high signal intensity in close contact with the tricuspid valve protruding into the right ventricle (small arrows). Note also the pericardial and left ventricular wall extension of similar high-intensity cysts with low-intensity partition (large arrows). (D) ECG-gated MRI, transaxial view (0.5 T, SE 750/ 30 ms), showing a cystic mass close to the mitral valve (arrow). LA= left atrium; LV= left ventricle. (E) ECG-gated MRI, transaxial view (0.5 T, SE 750/30 ms), showing hydatid tissue protruding into the left atrium (LA) (arrow), mimicking a myxoma. (Courtesy of Dr. von Sinner and Eur Radiol, 1995).

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Fig. 3.114 A 20-year-old Saudi man with primary hydatid cyst (HC) of the pericardium and right ventricular wall. (A) ECG-gated MRI, transaxial view (1.5 T, SE 1523/20 ms), showing the hydatid cyst bulging into the right ventricular cavity (RV). LV=left ventricle. (B) ECG-gated MRI, sagittal view (1.5 T, SE 1374/20 ms), showing the anterior, high signal intensity hydatid cyst to good advantage. (Courtesy of Dr. von Sinner and Eur Radiol, 1995).

Fig. 3.115 A 49-year-old Saudi man with hydatid cyst after previous rupture of a pericardial hydatid into the pericardium, with bulging left ventricle (LV) after a myocardial infarction due to aneurysm with thrombotic masses. ECG-gated MRI, transaxial view (1.5T, SE 600/20 ms), shows residual of ruptured hydatid cyst (arrow). (Courtesy of Dr. von Sinner and Eur Radiol, 1995).