We describe presence of an unusual right atrial membrane in a 30-year old female with end stage renal disease, hypertension and peripheral vascular disease. The patient was scheduled for midline sternotomy and pericardiotomy and removal of a migrated vascular stent in the right pulmonary artery. An intraoperative transesophageal echocardiogram (TEE) revealed an unusual membranous structure with fenestrations that stretched across the right atrium with attachments superiorly at the free wall and inferiorly at the inter-atrial septum. There was no evidence of flow obstruction across the tricuspid valve. Some of the considerations for the likely diagnosis of this structure were a prominent Eustachian valve, persistent Chiari network, aneurysmal inter-atrial septum, an inter-atrial septal cyst or Cor triatriatum dexter (CTD).
Keywords: Cor triatriatum dexter, Embryologic remnant, Right atrial membrane
How to cite this article: Aldawoodi NN, Arora H, Kumar PA. Incidental discovery of an unusual right atrial membrane in an adult patient. Ann Card Anaesth 2012;15:309-11
How to cite this URL: Aldawoodi NN, Arora H, Kumar PA. Incidental discovery of an unusual right atrial membrane in an adult patient. Ann Card Anaesth [serial online] 2012 [cited 2021 May 11];15:309-11. Available from: https://www.annals.in/text.asp?2012/15/4/309/101870
An informed consent was obtained from the patient's family regarding the publication of this case. A 30-year old female with end stage renal disease (ESRD) secondary to polycystic kidney disease, hypertension, peripheral vascular disease and acute on chronic pancreatitis was transferred to our hospital in respiratory distress for the removal of a suspected foreign body in her right pulmonary artery. She reported that a few years prior, she had a vascular stent placed in her left femoral loop graft, and since then she has been on hemodialysis via the loop graft. As a part of the workup for respiratory distress at the referring hospital, a chest CT scan had been obtained [Figure 1]. Based on the CT scan report, it appeared that the foreign body was a vascular stent that had migrated from the groin into the heart, and then lodged into the right pulmonary artery. Migrations of vascular stents, particularly those placed to extend A-V access for dialysis have been reported previously. 
Figure 1: An axial CT scan image showing the dislodged vascular stent in the right pulmonary artery as indicated by the black arrow
The interventional radiologists and cardiothoracic surgeons were consulted regarding removal of this foreign body. It was jointly decided that a percutaneous retrieval would be too risky, with concern that the cardiac valves may get damaged during the process. A surgical approach via a midline sternotomy incision was thus planned. Based on a review of the imaging studies, it was confirmed that there was an adequate segment of the right pulmonary artery proximal to the migrated stent to allow for the placement of a cross clamp. Had the foreign body been more proximally located, either nearer to or in the main pulmonary artery, it would have required the institution of cardio-pulmonary bypass (CPB). Nevertheless, CPB was available on standby, in case it became necessary. A pre-operative transthoracic echocardiogram (TTE) reported normal left ventricular function, moderate pericardial effusion and an otherwise unremarkable examination except for the presence of a patent foramen ovale (PFO).
The patient was taken to the operating room for removal of the migrated stent. After an uneventful induction of anesthesia, a left-sided double lumen tube was placed. An intraoperative transesophageal echocardiogram (TEE) performed for hemodynamic monitoring during the procedure revealed an unusual membranous structure with fenestrations, best visualized in the mid-esophageal four chamber view [[Figure 2] and [Figure 3]; Videos 1 and 2]. The membrane stretched across the right atrium with attachments superiorly at the free wall and inferiorly at the inter-atrial septum. On color flow Doppler examination, there was free flow across the fenestrations in the membranous structure which had been mistaken for a PFO on the pre-operative TTE exam.
Figure 2: 2D TEE mid-esophageal four chamber view with the probe slightly rotated to right, the white arrow shows the right atrial membrane
The echocardiographic findings were reviewed with the cardiac surgeons and cardiologists. Based on the patient's survival into adulthood, without any clinical symptoms attributable to this cardiac finding, and her serious co-morbid conditions, it was decided that an open cardiac surgical intervention to correct this anomaly was unnecessary and possibly too risky, especially since the foreign body retrieval did not necessitate CPB. Minimal surgical intervention to retrieve the foreign body was decided upon. The plan was to allow the patient to recover from the acute conditions, and once stable, to further investigate the membranous structure with a right heart catheterization.
The pericardium was opened via a midline sternotomy approach, and the right main pulmonary artery was dissected. The pulmonary veins on the right side were also dissected and isolated. The right pulmonary artery and vein were clamped, the right main pulmonary artery was opened and the stent easily retrieved. The pulmonary arteriotomy incision was repaired, clamps were removed and hemostasis achieved. The sternotomy incision was closed and the patient taken to the surgical intensive care unit in stable but guarded condition. The patient recovered from surgery with the resolution of her respiratory symptoms but had an involved post-operative course due to complications of acute pancreatitis and ESRD. A TTE examination performed post-operatively confirmed the presence of a fenestrated right atrial membrane with a worsening of the pericardial effusion along with the presence of fibrinous strands in the pericardial space, consistent with uremic pericarditis [Video 3]. A few weeks later, she died of sepsis before any further cardiac work-up could be performed.
The differential diagnosis of a right atrial mass includes thrombus, primary cardiac tumors such as myxoma, lipoma and sarcoma, metastatic tumors to the heart, vegetations, vestigial remnants, and congenital heart defects. Based on the size, shape, and location of the mass, as well as its mobility seen on echocardiogram, this differential can be narrowed down.  Some of the considerations for the likely diagnosis of this membranous structure were: A prominent Eustachian valve More Details, persistent Chiari network, aneurysmal inter-atrial septum, an inter-atrial septal cyst or cor triatriatum dexter (CTD). Another theory was that this membrane could have resulted from deposition of casts as the stent migrated through the right atrium into the pulmonary circulation. This would be more likely if the stent had lodged in the right atrium for an extended period of time before migrating further.
Cor triatriatum is a congenital cardiac anomaly in which an embryologic membrane persists in the right or left atria. Cor triatriatum sinister affects the left atrium and is the more common of the two, with an incidence of about 0.1% of all congenital cardiac conditions.  In CTD the membrane represents the embryonic sinus venosus remnant in the right atrium, with an incidence of around 0.025%.  The membrane separates the right atrium into an inlet and an outlet portion. The trabeculated anterior outlet chamber contains the atrial appendage and tricuspid valve and the posterior inlet chamber contains the inter-atrial septum, often with a PFO, into which the superior and inferior vena cava drain.  During the fourth week of embryonic development, the common atrium is separated from the venous sinus by the bi-leaflet venous sinus valve. By the twelfth week, the left leaflet becomes part of the septum secundum of the inter-atrial septum, and the right leaflet regresses leaving behind superiorly, the crista terminalis, and inferiorly, the Eustachian valve at the inferior vena cava junction and the Thebesian valve at the entrance to the coronary sinus. CTD occurs when the right leaflet fails to be reabsorbed. CTD can be associated with other right sided defects such as pulmonic stenosis or atresia, tricuspid valve (TV) abnormalities such as Ebstein anomaly, hypoplastic right ventricle (RV), and inter-atrial septal defects. A patient's clinical symptoms due to CTD depend on the degree of obstruction. The presence of a membrane can lead to trapped central venous catheters, arrhythmias or embolic phenomena. CTD can be diagnosed by echocardiography, CT angiography, right heart catheterization or MRI. Clinical presentation is dependent on the degree of septation. Incomplete septation or fenestrations within the membrane allowing for normal right atrium to RV blood flow often are found incidentally in adults, as in our patient.  Severe septation may cause life-threatening symptoms and often presents at a younger age and with cyanosis and failure to thrive.  Asymptomatic patients with CTD do not require correction whereas symptomatic patients will require surgical resection or percutaneous correction.  Case reports of adults have been described in whom CTD was incidentally discovered.  In one case, the insertion of the membrane was in the inter-atrial septum and the base of the right atrium, dividing the RA into two compartments with communication through fenestrations in the septum. In another case, the membrane began in the inter-atrial septum by the opening to the coronary sinus and then ran across the lateral side of the atrium down to the IVC. 
A prominent Eustachian valve, can cause right atrial separation into two functional chambers and therefore be confused with CTD.  Other embryologic remnants such as a prominent Thebesian valve or Chiari network, also caused by persistence of the right valve of the venous sinus can mimic CTD.  TEE is helpful in identifying incidental findings such as CTD in adult patients and in determining the degree of flow obstruction it may be causing.  A bubble study can be performed to confirm the separation of the right atrium into two separate compartments. TEE also helps distinguish this entity from an enlarged Eustachian valve or a Chiari network and whether or not there is an associated PFO or other associated congenital anomalies that may need to be addressed surgically.
Dashkoff N, Blessios GA, Cox MR. Migration of covered stents from hemodialysis A-V access to the pulmonary artery: Percutaneous stent retrieval and procedural trends. Catheter Cardiovasc Interv 2010;76:595-601. [PUBMED]