Discussion

Giant mobile left atrial masses are rare and carry exceptionally high embolic and obstructive risk. Classically, highly mobile left atrial masses are associated with thrombi occurring in the context of atrial fibrillation, rheumatic mitral stenosis, or severe left atrial enlargement [1,2].

Unlike classic left atrial thrombi, the present case demonstrated the absence of atrial fibrillation, the absence of significant mitral valve disease, the absence of marked left atrial enlargement, and a known metastatic malignant disease. Although the echocardiographic appearance initially suggested giant thrombus formation, histopathological analysis ultimately demonstrated neoplastic intravascular extension of metastatic malignant SFT. This distinction is clinically essential because imaging findings alone may not reliably differentiate thrombotic from neoplastic intracardiac lesions. Both entities may exhibit high mobility, multilobulated morphology, intracavitary extension, and dynamic prolapse through cardiac valves.

Definitive diagnosis therefore frequently requires histopathological examination.

SFTs are uncommon mesenchymal neoplasms with variable biological behavior [6-8]. While many SFTs follow an indolent clinical course, malignant forms may demonstrate local recurrence, distant metastases, vascular invasion, and aggressive progression [7-9].

Cardiac involvement by SFT is exceptionally rare, with only a small number of cases reported in the literature [5,10]. Potential mechanisms include hematogenous dissemination, direct intravascular extension, and metastatic intracardiac implantation [5]. In the present case, extension occurred by direct intravascular growth through the left superior pulmonary vein into the left atrium, a mechanism also described in previously reported cases (see comparison below).

The presence of STAT6 positivity strongly supports the diagnosis of SFT and represents a highly sensitive and specific immunohistochemical marker for these tumors [6]. The marked hemangiopericytoma-like vascular pattern observed in this case is also characteristic of SFT and supports the pathological diagnosis [8].

Intracardiac extension of malignant SFT has been described in only a handful of prior reports, most involving direct transvenous extension into the left atrium via a pulmonary vein, though hematogenous spread to multiple chambers has also been reported. Table 1 summarizes previously published cases alongside the present report.

Study | Age/sex | Primary site | Route of cardiac extension | Chamber(s) involved | Treatment | Outcome
Cuadrado et al. [11] | 74, F | Pleura | Intracavitary extension via the left upper pulmonary vein | LA | Surgical resection of the primary tumor | Not detailed in report
Hashmi et al. [12] | 67, F | Pleura (recurrent) | Invasion of the left inferior pulmonary vein into the LA | LA | Pneumonectomy + LA mass resection, with pericardial patch | Died in-hospital, day 107 (multiorgan complications)
Suzuki et al. [13] | 24, F | Forearm (soft tissue), then pleura | Left atrial endocardium (mechanism not specified) | LA | Resection of forearm, pleural, and LA tumors | Not detailed in report
Alonso et al. [14] | 87, M | Pleura | Hematogenous (multiple chambers) | RV free wall, interventricular septum, LV free wall | None (systemic metastatic disease) | Died (massive pulmonary thromboembolism)
This study | 63, F | Left anterior mediastinum | Intravascular extension via the left superior pulmonary vein | LA | Surgical resection (aortopulmonary window approach + LA tumor resection) | Not available

As illustrated in Table 1, direct transvenous extension into the left atrium via a pulmonary vein, as in the present case, is the most frequently reported route, though the interval between diagnosis of the primary tumor and cardiac involvement, as well as outcomes, varied considerably across reports, ranging from surgical resection with short-term survival to rapid postoperative or disease-related death. This variability underscores the aggressive and unpredictable natural history of malignant SFT once cardiac extension occurs.

The differential diagnosis of a giant, mobile left atrial mass includes left atrial thrombus, cardiac myxoma, primary cardiac sarcoma, tumor thrombus (e.g., renal cell carcinoma extending via the inferior vena cava), and metastatic extension through the pulmonary veins, as occurred in this case [5,15]. Left atrial thrombus is by far the most common etiology and is favored by a background of atrial fibrillation, mitral stenosis, or marked atrial enlargement, none of which were present here. Cardiac myxoma typically arises as a pedunculated mass with a discrete stalk attached to the region of the fossa ovalis and tends to be more homogeneous in echotexture. Primary cardiac sarcomas are usually broad-based, heterogeneous, and may show hypoechoic areas corresponding to necrosis, with a propensity for local invasion rather than a stalk. Tumor thrombus and metastatic transvenous extension, as in the present case, are suggested by direct continuity between the mass and an adjacent venous structure, though this continuity can be difficult to appreciate on two-dimensional echocardiography alone [15].

In this case, preoperative diagnosis remained difficult because the absence of atrial fibrillation and mitral valve disease argued against a classic thrombus without excluding a neoplastic one, and because extreme mobility with multilobulated morphology can be seen with both thrombus and tumor. No dedicated cross-sectional imaging (computed tomography/magnetic resonance imaging) was obtained, given the urgency of the presentation, and the known history of metastatic SFT raised suspicion for neoplastic involvement without confirming a cardiac origin in the absence of tissue diagnosis. Ultimately, only histopathological examination, which revealed the transvenous route of extension and STAT6 positivity, established the definitive diagnosis.

Echocardiography was central to the detection of the intracardiac lesion, the characterization of size and mobility, the assessment of mitral valve interaction, the evaluation of embolic and obstructive risk, and the guidance of therapeutic decision-making. Transesophageal echocardiography provided superior anatomical resolution and allowed detailed evaluation of the lesion morphology, the dynamic transmitral prolapse, the intracardiac extension, and the absence of associated valvular disease.

The repetitive prolapse of the mass through the mitral valve created a physiology similar to intermittent “ball-valve” obstruction, potentially capable of causing sudden hemodynamic collapse.

Management of intracardiac neoplastic masses remains challenging, particularly in patients with advanced metastatic malignancy. Potential therapeutic options include anticoagulation, surgical resection, systemic oncologic therapy, or palliative management.

A giant, highly mobile, multilobulated echodense mass prolapsing through the mitral valve is the classic echocardiographic description of a ball-valve left atrial thrombus, and given that thrombus is statistically far more common than neoplastic intracavitary extension, it was reasonably considered the leading initial diagnosis. Empiric therapeutic anticoagulation was instituted immediately, as is standard first-line management for any newly identified highly mobile intracavitary mass with embolic potential, since delaying treatment while awaiting definitive characterization would itself have carried embolic risk.

Because the tumor extended transvenously through the left superior pulmonary vein, operative resection required a combined surgical exposure through the aortopulmonary window together with left atriotomy to achieve removal of both the intracavitary and venous components. Resection in the setting of known widespread metastatic disease also required balancing complete oncologic clearance against operative risk in a patient with limited overall prognosis.

Because thrombus and neoplastic intravascular extension can be clinically and echocardiographically indistinguishable, and because their management differs fundamentally, histopathological confirmation was considered essential before any long-term therapeutic strategy could be defined; surgery therefore served the dual purpose of definitive treatment and diagnostic confirmation.

In the present case, urgent surgical intervention was favored because the lesion was highly mobile with an imminent embolic risk, a possible acute mitral inflow obstruction, and a sudden cardiovascular death risk. Therapeutic decision-making required balancing the operative risk, the metastatic disease burden, the oncologic prognosis, and the immediate cardiovascular danger.

This case emphasizes the importance of multidisciplinary collaboration involving cardiology, cardiac surgery, oncology, imaging specialists, and pathology.

This report has several limitations. Postoperative imaging surveillance, recurrence status, adjuvant oncologic therapy, and long-term survival data were not available at the time of manuscript preparation, precluding assessment of recurrence risk and long-term outcome, both of particular importance given the recognized potential for local recurrence and metastasis in malignant SFT [7,8].

Preoperative diagnostic workup was limited to transthoracic and transesophageal echocardiography; cross-sectional imaging (computed tomography/magnetic resonance imaging) and dedicated spectral Doppler assessment of the mass were not performed, given the urgency of the clinical presentation, and could have provided additional information regarding tissue characterization, vascular continuity with the pulmonary vein, and enhancement pattern [15].

Finally, the immunohistochemical panel was limited to STAT6; additional markers supportive of SFT and of prognostic value in malignant variants (CD34, BCL-2, CD99, Ki-67 proliferation index) were not assessed, and a formal quantitative mitotic count and margin status were not reported. Future studies and case reports would benefit from more complete pathological characterization and structured long-term follow-up to better define the natural history of intracardiac extension of malignant SFT.