IgG4-Related Disease masquerading as a cardiac tumor: A rare case involving the interatrial septum

Description of Clinical Presentation: IgG4-related diseases (IgG4-RD) are characterized by systemic fibroinflammation and infiltration of IgG4-positive plasma cells, which can affect various tissues and organs. It is more prevalent in men over 50 years of age in most cases. Cardiovascular involvement in IgG4-RD can manifest in various ways, including coronary artery and valvular disease, pericardial thickening, and the formation of cardiac masses or pseudotumors. These manifestations can precede or occur with IgG4-RD in other organs.
A 71-year-old man from São Paulo (Brazil), asymptomatic with a history of kidney and pancreatic cysts underwent abdominal magnetic resonance imaging follow up. Images of the upper abdomen incidentally identified a cardiac mass in the interatrial septum. There were no abnormal laboratory tests. The electrocardiogram showed first-degree atrioventricular block. A transthoracic echocardiogram revealed a mass in the interatrial septum, invading both atria and measuring 5.8 x 3.6 cm, with normal left ventricular systolic function. Cardiac magnetic resonance imaging (CMR) was perfomed.

Diagnostic Techniques and Their Most Important Findings: CMR demonstrated in cine images a cardiac mass with lobulated contours centered on the interatrial septum (figure 1), measuring 6.5 x 5.8 x 5.1 cm, without chambers obstruction. Isointense signal in T1-weighted sequence and heterogeneous intensity in T2 with minimal retention of paramagnetic contrast during perfusion sequences (figure 2). The mass presented intense and homogeneous late gadolinium enhancement (figure 1). For diagnostic confirmation, fluorodeoxyglucose positron emission tomography demonstrated global uptake of the radioactive tracer (figure 3). Subsequently, cardiac surgery was performed with resection of the tumor, followed by anatomopathological study with immunohistochemistry diagnosing a sclerotic lesion with an inflammatory process rich in IgG4-positive plasma cells. The patient is asymptomatic receiving corticosteroid therapy and being monitored by a rheumatologist. A postoperative echocardiogram showed no evidence of cardiac mass.

Learning Points from this Case: IgG4 disease can present as tumor masses mimicking neoplasms in any organ. In the heart, the most common involvement occurs in the coronary arteries and valves. Myocardial involvement is rare. Diagnosis usually requires multimodal imaging analysis, and the challenges of characterizing masses and tumors can be overcome with the use of CMR, which features numerous sequences in its acquisitions capable of differentiating tissue, edema, fibrosis, and vascularization. Early recognition of IgG4-related Disease is valuable, given the potentially reversible treatment with immunosuppressants.

Steady State Free Precession and late gadolinium enhancement sequences
Perfusion sequences
PET-CT showing cellular activity