Interatrial septal aneurysm mimicking an atrial myxoma on multiparametric cardiovascular magnetic resonance imaging

Abstract

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Interatrial septal aneurysm (IASA) appears as a localised saccular deformity usually detected during routine echocardiography or stroke evaluation. Imaging hallmarks are >15mm prolapsing motion across the interatrial septum (IAS) and identical content to blood-pool, which are in contrast to this patient. Clinical case An 81-year-old asymptomatic man underwent transesophageal echocardiographic (TEE) right atrial mass assessment revealing a well-circumscribed, mobile mass attached to the interatrial septum suggestive of myxoma. Given previously-excised renal cell carcinoma, gadolinium contrast-enhanced cardiovascular magnetic resonance (CMR) imaging was performed for mass characterisation. Mass signal intensity (SI) was distinct to blood-pool, in keeping with mass content not being blood. Cine imaging revealed an isointense, mobile mass (Figure 1, Video 1) attached to the fossa ovalis. The mass was of intermediate SI isointense to myocardium on T1-weighted, and bright and hyperintense on T2-weighted imaging. First-pass perfusion (Video 2) and early enhancement imaging demonstrated a hypointense, non-perfusing mass. The mass hyperenhanced on late enhancement imaging excluding the differential of thrombus. Imaging findings were entirely consistent with atrial myxoma. Intraoperatively, the excised mass was actually confirmed as an IASA with exquisitely tight neck. Discussion This is the first case of IASA mimicking atrial myxoma on CMR imaging. We postulate that it behaved like a non-perfusing mass as its uniquely narrow neck resulted in extremely slow flow in and out. This permitted minimal blood with contrast entry which remained ‘trapped’ within, resulting in distinct SI to blood pool, and late hyperenhancement. Left atrial pressures forced the mass into the right atrium, preventing typical lateral IASA motion. Conclusion The diagnosis of IASA is best established with TEE while CMR imaging is the reference standard imaging modality for tissue characterization. It is vital to be able to identify and differentiate such entities to avoid misdiagnosis of an IASA as a cardiac myxoma or a malignant cardiac tumour. Nevertheless, we recognize the presence of limitation of imaging in this extraordinary case. Abstract Figure 1