Discussion

The term cor triatriatum dextrum had first been described by Reference YaterYater,Reference Yater ⁴ whereas the first clinical description in the literature was given by Rossall and Caldwell,Reference Rossall and Caldwell ⁵ when they described near-complete obstruction of venous flow from the inferior caval vein to the right atrium in a 19-year-old patient. A review of 1940 heart specimens at cardio-pathological museum of the Children’s Hospital of Pittsburg identified 14 specimens with prominent remnants of the embryonic right valve.Reference Trento, Zuberbuhler and Anderson ⁶ Of those, two patients had divided right atrium, but only one was diagnosed preoperatively. Embryologically, the divided right atrium arises from the sinus venosus valve, which is composed of the right and left venous valves. The left venous valve joins the atrial septum secundum, whereas the right regresses to leave the Thebesian and Eustachian valves.Reference Gerlis and Anderson ⁷ The divided right atrium results from failure of regression of the right venous valve around the 12th embryonic week.Reference Trakhtenbroit, Majid and Rokey ⁸ However, there is variable degree of regression failure whereby we occasionally see, on echocardiogram, what we call prominent Chiari network without evidence of obstruction as noted by Trento et al.Reference Trento, Zuberbuhler and Anderson ⁶ The presence of intra-atrial obstruction can interfere with the normal development of the right side of the heart and thereby explains some of the associated lesions with hypoplasia of the right-heart structures.Reference Trento, Zuberbuhler and Anderson ^{6 ,} Reference Trakhtenbroit, Majid and Rokey ⁸

Clinical presentation depends on the degree of obstruction and associated lesions. It is more likely to be associated with hypoplasia or obstruction of the right side. The degree of intra-atrial obstruction could lead to early presentation with ascites, hepatic failure, and peripheral oedema. It can also lead to chylothorax such as in our case. The patient may present at a later age with cyanosis because of streaming of the blood across an atrial communication.Reference Raffa, Al-Ibrahim, Kayali and Sorefan ^{9 –} Reference Jones and Niles ¹¹ One case presented with recurrent syncope and sudden death because of a sail-like structure that obstruct the right ventricle inflow,Reference Jones and Niles ¹¹ although others might be misdiagnosed because of misleading echocardiographic images confusing it with more common lesions such as Ebstein’s anomaly.Reference Salam, Gallacher and Uzun ¹² The majority of cases with prominent Chiari network with no obstruction or minor obstruction will pass undetected.Reference Trakhtenbroit, Majid and Rokey ^{8 ,} Reference Yarrabolu, Simpson and Virani ¹³

Echocardiography is usually diagnostic and will suffice in most casesReference Alboliras, Edwards, Driscoll and Seward ¹⁴ to plan and proceed with the surgical management. However, associated lesions might require further imaging and haemodynamic information for better planning complex cases. In our case, we presented the role of cardiac MRI in providing both anatomic and haemodynamic information to better guide the surgical procedure of choice, especially that a combination of right- and left-sided venous obstruction is extremely unlikely and, to the best of our knowledge, has never been reported before in the literature. The role of cardiac MRI in defining pulmonary vein abnormalities is well described and is more accurate than echocardiography alone.Reference Masui, Seelos, Kersting-Sommerhoff and Higgins ¹⁵ In the divided right atrium, there is one previous publication describing the technique and imaging in a 70-year-old patient, who presented with features of congestive heart failure and peripheral oedema.Reference Joe, Poustchi-Amin and Woodard ¹⁶ The technique and sequences were modified in our case, as the technology has improved, and the size and weight of our patient are significantly smaller.

Treatment is mainly surgical. However, interventional palliation has also been reportedReference Savas, Samyn, Schreiber, Hauser and O'Neill ¹⁷ that can temporarily improve the patient general condition in preparation for surgery. Surgical correction is relatively straightforward and uncomplicated, barring the associated lesions that can coexist. Careful and adequate resection of the obstructing fibromuscular structure is crucial. The gradient may persist if inadequate resection is performed, and cavo-atrial wall perforation may occur with aggressive resection. Great deal of attention should be paid to the coronary sinus and atrio-ventricular node during resection. Repair of the associated cardiac anomalies is performed in a standard manner.

In conclusion, this report and review is intended to present three important points

1. 1. To report previously unreported, left and right intra-atrial obstruction, and pulmonary vein stenosis.

2. 2. The role of cardiac MRI in outlining the pathology and associated lesion.

3. 3. Variable modes of presentation of such rare pathology through this case as well as literature review.