FM can be idiopathic or secondary, and most cases of secondary FM have infectious or non-infectious etiologies. The infectious etiologies include histoplasmosis, blastomycosis, coccidiomycosis, aspergillosis, and tuberculosis. The noninfectious etiologies include sarcoidosis, silicosis, rheumatoid arthritis, systemic lupus erythematosus, antineutrophil cytoplasmic antibody-associated vasculitis, IgG4-related disease, Riedel’s (fibrous) thyroiditis, and Behçet’s syndrome, tumor, and radiation or drug therapy [4,5,6]. We excluded secondary causes during the diagnosis, and the final diagnosis was idiopathic FM.
The two main imaging features of FM are local soft tissue masses around the mediastinum and diffuse mediastinal infiltration . Diffuse mediastinitis can affect the large blood vessels of the heart. Li et al. reported a case of pulmonary vein stenosis caused by FM. Their color Doppler flow imaging (CDFI) showed a high-speed blood flow signal from the pulmonary vein in the left atrium, indicating pulmonary vein stenosis, but two-dimensional echocardiography did not directly show the lesions around the pulmonary vein . Pereira-da-Silva et al. reported a case of FM with a mass in the right atrium and thickening of the aortic wall . Their echocardiographic findings were similar to ours, but their echocardiography did not show a complete lesion.
The current case is very rare, in that the lesion had extensive invasion of the heart and had imaging features indicative of FM. Five specific features made our case unique. First, there was diffuse proliferation of fibrous tissue that invaded multiple chambers. Second, the lesion mainly invaded the large blood vessels of the heart, with further involvement of the atria and the ventricles. Third, the soft tissue mass was wrapped extensively along the anatomical structures of the heart, resulting in lumen stenosis. Fourth, the lesion protruded into the atrium and formed a soft tissue mass. Fifth, soft tissue masses infiltrated the myocardium. In addition, our CDFI showed a high-speed blood flow signal in the narrow pulmonary arteries and pulmonary veins.
The imaging findings of FM may suggest its etiology. Sherrick et al. reviewed the records of 33 patients with FM and found that the most likely etiology of the 27 localized cases was histoplasmosis, and the most likely etiology of the 6 diffuse cases was idiopathic or non-infectious . Although there are some different interpretations, other studies reported diffuse cases without clear etiology. Our imaging features showed that the patient had diffuse disease, consistent with a diagnosis of idiopathic FM.
It is very rare for diffuse lesions to invade the heart, and a differential diagnosis to exclude tumors is necessary. Unfortunately, there are limited studies on the use of echocardiography to distinguish tumor from FM, especially because heart tumors are rare. We suggest two criteria to distinguish these two conditions. First, a malignant tumor mainly infiltrates the heart, but FM mostly encapsulates or wraps the heart. Second, a tumor may invade any part of the heart with no fixed pattern, but FM usually grows along the large blood vessels and then down to the atria and ventricles.
Encapsulated growth may also be encountered in Erdheim-Chester disease (ECD), whose imaging features are very similar to those of FM. ECD is a non-Langerhans histiocytosis of unknown origin. Its most common cardiac manifestation is a pseudotumor close to the right atrium that invades the right atrium and atrioventricular groove. Soft tissue masses also form around the aorta, pulmonary arteries, and their branching vessels . Because FM and ECD are rare diseases with no specific imaging characteristics, histopathology is needed for a definitive diagnosis.
The diagnosis of FM is the most important element of the current case. Although CT and MRI can provide more comprehensive information, echocardiography has the advantages of being more readily available, less expensive, and radiation-free. Thus echocardiography may help in the diagnosis and management of FM. Although echocardiography does not eliminate the need for other imaging techniques, such as CT and MRI, it may allow clinicians to reduce their use during follow-up. The extensive cardiac involvement in the current case suggests this may be a prerequisite for the application of echocardiography. In addition, ultrasound has high resolution and provides a good visualization of soft tissue. Coupled with CDFI, it can be used to determine the possible nature of lesions. Although there are no echocardiographic criteria for the diagnosis of FM, our study shows that echocardiography can aid in the diagnosis of FM.