Discussion
The transverse sinus is a pericardial reflection which is between the arterial mesocardium and the venous mesocardium. Existence of epicardial fat between ascending aorta and transverse sinus is a normal finding however, presence of fat pad in the sinus adjacent to LAA is rare and misleading. Epicardial fat surrounding the left pulmonary artery recess but not in TS was previously reported by Johner et al in Cardiology journal 2019[2]. They were not familiar with this anatomic variation around LAA and cancelled the cardioversion for atrial fibrillation (AF) due to LAA thrombosis!
As far as we know this is the third case of TSFP reported in literature. First case was introduced by Chhabra et al [5] and the second case was presented with Pergolini et al both in 2019[6]. None of these studies evaluated the patient with 3D technique. In our experience 3D mapping is a useful modality since the echodensity features in 3D mapping of thrombosis is different from fat pad and an expert echocardiologist can differentiate these two easily. In present patient the increased epicardial fat pad around RV was also noted. The similarity of the density between RV fat pad and TS lesion is another clue that this is not a thrombosis.
Although 2D TEE has higher resolution than 3D mapping due to higher frame rate, 3D mapping technology allows more comprehensive evaluation of LAA anatomy and its nearby structures. Its ability to differentiate the borders between LAA and adjacent structures made 3D TEE a feasible and reliable tool before invasive procedures such as LAA device closure.
Low velocity in LAA increases the risk of thrombosis formation however the absence of smoky pattern is in contrast with thrombosis in LAA. Several TEE angulations can prove the TSFP originates from outside the LAA in contrast with thrombosis. In addition, utilization of other imaging modalities such as CT scan and MRI may help diagnosis this anatomic variation.