Partially calcified organized thrombus of the right atrium mimicking a cardiac tumor: a case report

Abstract

Partially calcified organized thrombi of the right atrium are rare and may mimic cardiac tumors, making preoperative diagnosis challenging. A 60-year-old man was found to have a partially calcified right atrial mass during evaluation for atrial flutter. Despite anticoagulation therapy, the lesion persisted and a neoplastic process could not be excluded. Therefore, surgical resection was performed through a right mini-thoracotomy approach. Histopathological examination revealed a chronic organized thrombus with focal calcification and hemosiderin-laden macrophages. The postoperative course was uneventful, and no recurrence was observed during 2 years of follow-up. This case highlights the diagnostic challenge of partially calcified right atrial masses and suggests that a minimally invasive approach may provide a useful option for both diagnosis and treatment in selected patients.

Introduction

Partially calcified organized thrombi of the right atrium are uncommon intracardiac lesions and may occasionally present as mass-like structures on cardiac imaging [1]. In particular, they may closely mimic primary cardiac tumors, making definitive preoperative diagnosis challenging. Because imaging findings are often inconclusive, surgical resection may be required not only to prevent potential embolic complications but also to establish a pathological diagnosis. Minimally invasive cardiac surgery (MICS) has emerged as an alternative to median sternotomy for selected intracardiac lesions and may facilitate diagnosis and treatment with reduced surgical trauma.

Here, we report a rare case of a partially calcified, organized thrombus in the right atrium that persisted despite anticoagulation therapy and was successfully resected via a right mini-thoracotomy.

Case report

A 60-year-old man with a body surface area of 1.96 m² was found to have a right atrial mass during echocardiographic evaluation performed during catheter ablation for atrial flutter. Transesophageal echocardiography revealed a mass measuring 9.5 × 7.0 mm located on the right atrial septum. Contrast-enhanced computed tomography confirmed a partially calcified mass at the same location (Fig. 1). Following the ablation procedure, sinus rhythm was maintained. Although direct oral anticoagulant therapy was initiated, the mass persisted without regression. Given the persistence of the lesion despite anticoagulation therapy, the potential risk of embolic events, and the inability to exclude a neoplastic lesion, surgical resection was planned for both diagnostic and therapeutic purposes. Preoperative evaluation revealed preserved cardiac function without significant valvular or coronary artery disease.

Figure 1.

Preoperative contrast-enhanced computed tomography. A right atrial mass is identified on contrast-enhanced cardiac computed tomography. (A) Axial view. (B) Sagittal view. (C) Coronal view. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

A right mini-thoracotomy was performed through the fourth intercostal space. Cardiopulmonary bypass was established with arterial cannulation of the femoral artery using a 21-Fr HLS arterial cannula (Getinge, Gothenburg, Sweden). Venous drainage was achieved using a 29-Fr NexGen venous cannula (Medtronic, Minneapolis, MN, USA) inserted through the femoral vein under transesophageal echocardiographic guidance. The guidewire and cannula tip were carefully advanced and positioned within the inferior vena cava to avoid interference with the mass. In addition, a 20-Fr venous cannula (Pacífico; Senko Medical Instrument, Tokyo, Japan) was directly inserted into the superior vena cava to establish bicaval venous drainage while minimizing manipulation around the lesion. The superior and inferior vena cava were encircled with tapes. After aortic cross-clamping, antegrade cardioplegia was administered through the ascending aorta to achieve cardiac arrest. Following snaring of the superior and inferior vena cava, the right atrium was opened, revealing a mass located at the inferior margin of the fossa ovalis (Fig. 2A). An incision was made along the inferior margin of the fossa ovalis. The lesion was then resected en bloc with an adequate margin, including the adjacent right atrial wall (Fig. 2B and C). The right atrial defect was closed primarily (Fig. 2D). Cardiac activity was restored after closure of the right atrium, and the patient was weaned from cardiopulmonary bypass without difficulty.

Figure 2.

Intraoperative findings (surgeon’s view). (A) The right atrium is opened, revealing the mass. (B) An incision is made along the inferior margin of the fossa ovalis. (C) The mass is resected en bloc with an adequate margin. (D) The right atrial defect is closed primarily without the use of a patch. RA, right atrium.

The resected mass appeared macroscopically as a partially calcified thrombus-like lesion (Fig. 3A and B). Histopathological examination demonstrated a hypocellular lesion composed predominantly of hyalinized collagen fibers with focal calcification (Fig. 3C). Focal accumulation of hemosiderin-laden macrophages was observed, with no evidence of malignancy (Fig. 3D and E). These findings were consistent with an organized thrombus. The postoperative course was uneventful, with no evidence of embolic complications. Echocardiography revealed no residual mass or intracardiac shunt. The patient was discharged in good condition without arrhythmia. No recurrence has been observed during 2 years of follow-up.

Figure 3.

Macroscopic and histopathological findings. (A) Macroscopic view of the resected mass from the anterior side, showing a partially calcified, thrombus-like lesion. (B) Posterior view of the specimen, revealing thrombus-like contents. (C) Hematoxylin and eosin staining at low magnification (objective lens ×4) demonstrating focal calcification within the lesion. (D) Hematoxylin and eosin staining at intermediate magnification (objective lens ×10) showing a hypocellular lesion composed predominantly of hyalinized collagen fibers. (E) Hematoxylin and eosin staining at high magnification (objective lens ×20) demonstrating hemosiderin-laden macrophages.

Discussion

The present case demonstrates the difficulty of distinguishing a partially calcified organized thrombus from a cardiac tumor using preoperative imaging alone. Because the lesion persisted despite anticoagulation therapy and remained diagnostically indeterminate, surgical resection was required for both diagnosis and treatment. Histopathological examination ultimately established the definitive diagnosis of an organized thrombus. This case also illustrates that, in selected patients, a minimally invasive approach can facilitate both definitive diagnosis and complete treatment.

Histopathological examination demonstrated hyalinized collagen fibers, focal calcification, and hemosiderin-laden macrophages, findings consistent with a chronic organized thrombus. Calcification within a right atrial thrombus is uncommon and likely reflects a longstanding process of thrombus organization and remodeling. Previous reports have described calcified right atrial thrombi that persisted despite anticoagulation therapy and required surgical excision because of the potential risk of embolic events [2, 3]. Similar to these reports, surgical resection was considered appropriate because the lesion persisted despite anticoagulation therapy and remained diagnostically indeterminate. The mechanism of thrombus formation in the present case remains uncertain. Atrial flutter may have promoted local blood stasis, while embryological remnants such as the Eustachian valve or Chiari network have been implicated in thrombus formation near the fossa ovalis [3, 4]. Together, these factors may have contributed to thrombus development in the present patient.

MICS via a right mini-thoracotomy has been shown to be a safe and effective alternative to median sternotomy for selected cardiac masses, offering reduced surgical trauma and shorter hospital stay [5–8]. In previous reports of MICS for cardiac mass resection, mass size ranged from 1 to 16 cm², and right atrial lesions accounted for ~7%–15% of cases [5, 6, 8]. The feasibility of this approach depends largely on lesion size, anatomical location, and the ability to obtain adequate operative exposure. In addition, careful venous cannulation is essential in patients with right atrial masses to avoid interference with the lesion and potential fragmentation. In the present case, the lesion was small and localized near the inferior margin of the fossa ovalis, allowing sufficient exposure through a right mini-thoracotomy. Furthermore, transesophageal echocardiographic guidance and bicaval venous drainage enabled safe establishment of cardiopulmonary bypass while minimizing manipulation around the mass. This experience suggests that MICS may represent a useful and less invasive option for selected right atrial masses requiring both definitive diagnosis and treatment.

We report a rare case of a partially calcified organized thrombus of the right atrium that mimicked a cardiac tumor and required surgical diagnosis. In selected patients with diagnostically challenging right atrial masses, a right mini-thoracotomy approach may provide a useful and less invasive option for both definitive diagnosis and treatment.

Author contributions

T.T. drafted the manuscript and collected the clinical data. H.K. supervised the manuscript preparation and revised it critically for important intellectual content. H.N. provided surgical supervision and contributed to the operative strategy. S.I., T.Y., and Y.I. participated in the patient’s surgical treatment and postoperative management. All authors read and approved the final manuscript.

Conflicts of interest

None declared.

Funding

The authors received no specific funding for this work.

Data availability

The data underlying this article will be shared on reasonable request to the corresponding author.

Ethics approval and consent to participate

This work does not require ethical considerations or approval.

Consent for publication

The authors confirm that written informed consent for submission and publication of this case report including images and associated text has been obtained from the patient in line with COPE guidance.