Differentiation between thrombus and masses in the atria is challenging. Identification of intracardiac masses on noninvasive imaging is clinically important because it determines and guides the treatment for the structure.

Left atrial cardiac myxoma is the most common primary cardiac tumor, representing 20% to 40% of intracardiac masses. The most common location for myxomas is the left atrium, attached to the atrial septum at the fossa ovalis, however they may be found in all four chambers of the heart^[1].

Another important cardiac mass is intracardiac thrombus. In rare situations, a thrombus may organize and attach to the atrial septum and have a similar appearance as other cardiac masses^[2]. Cardiac transplant patients are at increased risk for these complications as chronic immunosuppression increases the risk of malignancy, and various other factors often predispose them to thrombus formation. However, the correct diagnosis can sometimes be difficult with certainty only being achieved after histology examination^[3].

In this educational forum, we report a case of left atrial thrombus 16 years after orthotopic heart transplantation mimicking myxoma.

A 60-year-old patient underwent orthotopic heart transplantation in 2008 for end-stage heart failure secondary to dilated cardiomyopathy. The donor heart was from an 18-year-old man who had died as a result of brain injury after a road traffic accident. After heart transplantation, the recipient had two episodes of acute rejection which were treated with pulse steroid therapy, and he was diagnosed with cardiac allograft vasculopathy with non-significant coronary artery disease. Immunosuppression treatment consisted of prednisone, everolimus, and tacrolimus. In 2021, he underwent right nephrectomy due to Grawitz carcinoma. Neither the donor nor the recipient had a family history of cardiac tumors. In the year 2024, in a follow-up echocardiography, a rapidly growing left atrial mass measuring 39 × 28 × 31 mm located at the posterior atrial wall was diagnosed for the first time. Later, the patient underwent multimodality imaging where the diagnosis of left atrial myxoma was established (Figure 1). On the contrary, histology confirmed the diagnosis of organized left atrial thrombus. Based on the preoperative evaluation, the tumor was treated as left atrial myxoma, and the patient underwent urgent redo-surgery with the use of aortobicaval cardiopulmonary bypass. The pedicle of the left atrial tumor was attached to the posterior atrial wall, on the recipient’s site. The tumor was completely excised, and a suture was placed on the tumor’s stalk on the atrial wall (Figures 2A, 2B). The postoperative course was uneventful and on postoperative day eight, he was discharged. Histology examination showed organized left atrial thrombus (Figures 2C, 2D).

Fig. 1

Fig. 2

An informed consent was signed from the patient to present this report.

A. Is multimodality imaging always sufficient in the differential diagnosis of left atrial thrombus mimicking myxoma?

The case reported stands out because it shows the limitations of multimodality imaging where in cases of left atrial tumors with features highly suggestive of an atrial myxoma, it is insufficient to provide the correct diagnosis, which is made after examination of the pathology specimen.

Although multimodality imaging has a central role in the differential diagnosis of left atrial tumors, in cases of tumors with features highly suggestive of an atrial myxoma, it has some limitations.