Cardiac Sarcoidosis: The Challenge of Radiologic-Pathologic Correlation

Cardiac sarcoidosis is a rare but potentially fatal disorder with a nonspecific spectrum of clinical manifestations, including conduction disorders, congestive heart failure, ventricular arrhythmias, and sudden cardiac death. Although early treatment to improve morbidity and mortality is desirable, sensitive and accurate detection of cardiac sarcoidosis remains a challenge. Except for the histopathologic finding of noncaseating granulomas in an endomyocardial biopsy specimen, most diagnostic tests are limited and nonspecific at best. Therefore, the decision to initiate treatment is based largely on the patient’s clinical symptoms and the course of the disease, rather than histologic confirmation. Successful recognition of cardiac sarcoidosis ultimately requires rigorous collaboration among a clinician, radiologist, and pathologist. Advanced imaging modalities, such as cardiac magnetic resonance imaging and positron emission tomography with fluorodeoxyglucose, have become increasingly useful in facilitating diagnosis and therapeutic monitoring, although limited prospective studies exist. This article describes the clinical parameters and pathologic findings of cardiac sarcoidosis and the advanced imaging features and differential diagnostic challenges that must be considered for a successful diagnostic approach. In addition, to improve the understanding of abnormalities detected with different imaging modalities, we suggest a unified terminology in describing radiologic findings related to cardiac sarcoidosis.

TEACHING POINTS

■■ Histologic examination of an endomyocardial biopsy specimen that demonstrates noncaseating granulomas is the criterion standard, but this procedure is rarely performed and has a limited diagnostic yield of 20%–50%. The most widely adopted set of clinical criteria guiding diagnosis were established by the Japanese Ministry of Health and Welfare (JMHW). Treatment of CS is initiated largely on the basis of a measured consideration of symptoms, electrocardiography and advanced imaging findings, and disease course, rather than histologic confirmation.

■■ The rate of left ventricular dilatation was similar (25%) in patients who died of incidental sarcoidosis and those who died of CS with extensive involvement of the heart. Subepicardial scars were most common, followed by midmyocardial and subendocardial disease. Often, the scars are randomly distributed and may even involve the myocardium diffusely, without clear separation from uninvolved myocardium.

■■ According to the JMHW criteria, the diagnosis of CS is assigned to either of two scenarios. In the first scenario, CS is confirmed by the presence of epithelioid noncaseating granulomas at histologic examination of an endomyocardial biopsy specimen. The second scenario requires one or more of the following findings: conduction system abnormalities at ECG, functional and structural abnormalities at echocardiography, abnormal findings at nuclear medicine or cardiac magnetic resonance imaging, and interstitial fibrosis without granulomas identified at histologic examination of an endomyocardial biopsy specimen.

■■ Clinical experts agree that the following patients merit assessment for CS: (a) patients who have already received a diagnosis of extracardiac sarcoidosis and have cardiac symptoms and/or signs (including chest pain and 12-lead ECG or echocardiographic abnormalities); (b) patients younger than 55 years who have not received a diagnosis of sarcoidosis and who have unexplained conduction abnormalities, ventricular dysrhythmias, syncope, or nonischemic heart failure; and (c) patients with known CS (to document the severity of inflammation or the effect of immunosuppressive therapy).

■■ Accurate diagnosis of CS is difficult because of the overlap of both clinical and imaging findings with other inflammatory and infiltrative conditions affecting the heart. Myocarditis, dilated cardiomyopathy, hypertrophic cardiomyopathy, amyloidosis, and ARVC are often considered in the radiologic differential diagnosis. Appropriate clinical context is essential when considering CS, because of its broad and nonspecific spectrum of appearances at imaging.