Our article holds significance due to the rarity of the right atrial masses. Particularly, large atrial masses like these may be confused with each other until the intraoperative process due to nonspecific symptoms and lack of specific findings in imaging methods. Imaging methods such as transthoracic echocardiography and computed tomography are crucial diagnostic tools for assessing the size, location, and relationship of the mass with surrounding tissues. However, these methods do not always allow for a definitive diagnosis. Some masses may appear similar to myxoma in imaging tests but turn out to be metastatic malignant tumors. In some cases, thrombus formation may mimic myxoma. Differentiating these structures before surgery is important, but some cases can only be distinguished during surgery. In the first case, the considerable size of the mass is noteworthy as it does not elicit specific symptoms in the patient and does not impact heart functions on ECG and TTE. However, it is crucial to recognize that such sizable masses can impair tricuspid valve functions, induce dysfunction in the right ventricle, result in tumor embolization, and even lead to sudden death. Conversely, the second case is noteworthy for presenting a rare cardiac manifestation of a hydatid cyst. Upon reviewing the literature, few articles discuss the association between hydatid cysts and the heart. In this instance, the preservation of right heart functions despite the mass effect, the absence of sepsis development despite an ongoing infectious situation, and the prevention of cyst rupture, especially given its substantial size, are significant observations. Both cases were fortunate not to result in pulmonary embolism due to tumor embolization. It is pertinent to mention that myxomas represent the most common primary tumors in the heart, with approximately 15–20% located in the right atrium [4]. Typically found in the fossa ovalis region of the right atrium, myxomas very rarely attach to the atrium wall [5].

In the differential diagnosis of the right atrial masses, consideration should be given to various structures, including thrombus, myxoma, vegetation, tumor metastasis, interatrial septal pathologies, eustachian valve, and the Chiari network [6, 7]. Thrombus typically exhibits mobility and a lobulated character, with irregular edges. In contrast, myxomas are relatively fixed, characterized by smooth edges, and present as solid masses. The right atrial myxomas tend to be larger with a broader base. The most concerning complication associated with myxomas is their potential to obstruct the tricuspid valve. However, in our first case, despite the substantial size of the mass, it did not lead to valve obstruction or insufficiency. This is likely attributed to the fact that the mass was not attached to the interatrial septum but rather to the free wall of the right atrium.

In our second case, the fragmented structure of the mass, elevated infectious parameters, and the presence of fever were indicative of a vegetation. These findings highlight the importance of a comprehensive approach to differential diagnosis, considering both clinical and imaging features to accurately identify the nature of the right atrial masses. The consideration of vegetation persisted until the intraoperative phase, shaping the treatment plan accordingly. However, upon macroscopic examination, it became evident that the mass was, in fact, a hydatid cyst. Furthermore, the absence of the left ventricular wall motion defects, ischemic heart disease, any underlying clinical conditions predisposing to thrombogenicity, and the normal dimensions of the heart chambers collectively steered us away from the initial diagnosis of a thrombus.

Cardiac hydatid cysts are exceptionally rare, constituting approximately 1% of all hydatid cyst cases [8]. They are commonly located in the ventricles and interventricular septum, with the right atrial and pericardial involvement being extremely uncommon. Despite the diagnostic challenges, modalities such as transthoracic echocardiography (TTE), transesophageal echocardiography, cardiac computed tomography, and cardiac magnetic resonance imaging prove valuable in achieving a diagnosis. Surgical intervention stands as the definitive treatment, and postoperatively, the recurrence rate can be mitigated with medications such as albendazole and metronidazole. The rupture of a cyst bears the risk of disseminating the disease, potentially leading to sepsis. Macroscopically, myxomas can manifest in two distinct forms: the globular type, characterized by a round and smooth surface, and the polypoid type, featuring an irregular surface [9]. Additionally, myxomas are categorized into sporadic and familial types. The common sporadic type typically exhibits a typical location, while the rare familial type tends to present atypically, often in younger individuals, and may involve multiple structures [10]. Clinical manifestations and symptoms vary depending on the mass's location. Myxomas causing obstruction and insufficiency in the atrioventricular valve typically lead to complaints such as orthopnea, dyspnea, cough, hemoptysis, and rhythm disorders. In our case, the symptoms were not pronounced as the mass had minimal impact on the valves and right ventricular functions.

The left-sided myxomas may result in cerebrovascular disease, mesenteric ischemia, and renal infarction due to peripheral and systemic embolization. Additionally, nonspecific systemic symptoms such as fever, fatigue, weight loss, and joint pain may also be observed. Echocardiography holds a crucial role in the differential diagnosis of the right atrial masses. In cases where echocardiography proves insufficient, transesophageal echocardiography, cardiac computed tomography, and cardiac magnetic resonance imaging are valuable adjuncts. The standard treatment for myxomas is surgical excision. Patients inadequately resected, those with multiple structures, familial types, or those developing as tumor metastases have a higher recurrence rate [11]. Surgery should be promptly scheduled upon diagnosis due to potential complications such as acute valve obstruction, pulmonary embolism, and sepsis.