A Curious Case of Scimitar Syndrome That Defies Embryology

Abstract

Scimitar syndrome is a rare condition described by unique anatomic features that consist mainly of an abnormal connection of the right pulmonary veins to the inferior vena cava and right atrial junction, as well as an anomalous systemic arterial supply to the right lung. We present the case of a 60-year-old man with an atypical variant of scimitar syndrome that was embryologically perplexing and anatomically challenging to correct. We highlight key surgical and procedural considerations for a patient with scimitar syndrome presenting with this complex surgical anatomy.

Scimitar syndrome, a partially anomalous pulmonary venous connection, occurs in 1 to 2 in 100,000 live births and is characterized by drainage of the scimitar vein (SV) from the right lung to the inferior vena cava (IVC). Concomitant abnormalities may include right lung hypoplasia, atrial septal defects (ASDs), dextrocardia, or systemic to pulmonary collateral arteries branching from the abdominal aorta.¹ Clinical presentation ranges from neonates requiring immediate augmentation of pulmonary venous return to adults who are often asymptomatic or present with atrial fibrillation secondary to right atrial overload. Surgical indications in adults are pulmonary hypertension, recurrent lung infections, or large left-to-right shunts (pulmonary-to-systemic flow ratio [Qp/Qs] >1.5:1).¹ Scimitar anatomy is variable and can be grouped on the basis of which segments of pulmonary venous drainage are taken by the SV. The largest quantification of patients with scimitar syndrome to date describes 3 distinct patterns. In severe forms (57%), the SV drains the entire right lung, moderate forms (11%) include SVs draining the inferior and middle lobes, and in mild forms (28%), the SV drains only the right lower lobe.² Indeed, these patterns have been reported in many single-center studies and case reports,^1,3 yet only 1 anatomy similar to our patient’s has been identified.⁴ In this report, we discuss surgical intervention in a 60-year-old man with an atypical SV draining the right upper and middle lobes with a right lower lobe pulmonary vein draining to his left atrium, a seemingly impossible and peculiar embryologic anomaly (Supplemental Figure 1, discussion in the Supplemental Material).

Our patient’s scimitar anatomy was identified incidentally during computed tomographic (CT) calcium scoring study 6 years earlier for suspected coronary artery disease. He subsequently experienced obstructive sleep apnea, mild pulmonary hypertension, and 3 episodes of self-limiting symptomatic paroxysmal atrial fibrillation that was subsequently quiescent. At presentation, this patient had elevated pulmonary artery pressures (mean, 16 mm Hg) and a Qp/Qs ratio of 1.6:1. Preoperative CT angiography confirmed that the SV was draining the right middle and upper lobes to the IVC just distal to the IVC-right atrial junction, with a normally connected right lower pulmonary vein draining the right lower lung (Figure 1). The left atrium was more remote from the SV than anticipated, given the normal left lower pulmonary venous drainage.

Figure 1.

(A) Axial computed tomographic angiography of the scimitar vein (arrow) draining to the inferior vena cava. (B) Transverse 3-dimensional reconstruction of preoperative computed tomographic angiography.

After transesophageal echocardiography (TEE) confirmation of scimitar anatomy (Figure 2A), median sternotomy was performed, the phrenic nerve was identified, the right lung anatomy was inspected, and the pericardium was opened. The SV was dissected completely noting and encircling branches to the middle and upper lobes and its low entrance to the IVC (Figure 2B). The phrenic nerve was skeletonized. After heparin administration, the ascending aorta and superior vena cava were cannulated. With a long femoral cannula, the IVC was then cannulated through a right femoral vein access. Cardiopulmonary bypass was established, and a single dose of antegrade cardioplegia achieved cardioplegic arrest.

Figure 2.

Correction of the scimitar vein (SV). (A) Operative transesophageal echocardiography confirming scimitar vein anatomy. (B) Surgical view of the uncorrected scimitar vein. (C) Spatulated scimitar vein to the free right atrial wall. (D) Interatrial baffle. (E) Postoperative transesophageal echocardiography. (F) 3-dimensional reconstruction of postoperative computed tomographic angiography of the corrected scimitar vein draining through the right atrium to the left atrium. (IVC, inferior vena cava.)

The SV was controlled with vascular clamps and divided at its junction with the IVC while keeping as much length as possible, and the IVC opening was oversewn with 5-0 polypropylene (Prolene, Ethicon) suture. The length of the SV was inadequate for direct implantation into the left atrium without a synthetic graft extension or risk for kinking. Therefore, implantation into the right atrium with a short interatrial baffle was elected. The right atrium was opened, and a suitably large ASD was created through the fossa ovalis. Re-endothelization was performed by suturing the left atrial endocardium to the exposed interatrial tissue with running 5-0 Prolene suture. The spatulated SV was then sewn to an aperture in the right atrial wall with running 5-0 Prolene suture (Figure 2C), and a suitably sized bovine pericardial patch was used to create the interatrial baffle from the opening of the SV to the ASD (Figure 2D). The left atrial appendage was occluded using a 35-mm Gillinov-Cosgrove clip (AtriCure). A formal biatrial maze procedure was not performed given that the history of atrial fibrillation was remote. After cross-clamp removal, there was immediate return to normal sinus rhythm, and the right atrium was closed. The patient was weaned from bypass with excellent hemodynamics. TEE showed normal biventricular function with phasic flow through a widely patent SV and interatrial baffle (Figure 2E).

The patient was extubated on postoperative day 1. Postoperative CT angiography noted expected narrowing of the baffle as it passed through the ASD. This narrowing did not compromise the expected pulmonary venous return from the SV to the left atrium (Figure 2F). With all perioperative symptoms resolved, the patient was discharged on postoperative day 8.

Six weeks after discharge, the patient presented with dyspnea on exertion, shortness of breath, and elevated natriuretic peptide values. CT angiography showed relative patency of the SV and interatrial baffle (Figure 3A). Considering these symptoms, the baffle was electively stented. Given that no interatrial communication was present, a septostomy was required to dilate and stent the existing baffle (Figures 3B, 3C). The septostomy site was left open, with TEE showing a slight left-to-right shunt.

Figure 3.

Readmission and catheterization. (A) Computed tomographic angiography showing a patent yet restricted scimitar vein (SV) baffle. (B) Transcatheter angiography showing stent dilation of the baffle. (C) 3-dimensional reconstruction of computed tomographic angiography for a dilated scimitar vein baffle draining through the right atrium.

Comment

For patients with typical scimitar anatomy, our center has used the in situ pericardial roll.⁵ However, the unique anatomy in this case, with the right lower pulmonary vein draining to the left atrium, precluded creation of a pericardial roll. (Supplemental Figures 2A, 2C). Other potential options for direct implantation of the SV into the left atrium were also impossible given that the left atrium was remote and directly posterior to the right atrium (Supplemental Figures 2B, 2C); a wherein an interatrial baffle was therefore chosen despite the well-known limitations and proclivity for narrowing with this approach.¹ Although a surveillance CT scan of the repair before discharge resembled the follow-up CT scan, elective stenting of the baffle was performed.

As mentioned earlier, catheter-based intervention was common in conventional baffle techniques because of circuitous routes that are vulnerable to stenosis and thrombosis.^1,6 One relevant point for potential catheter-based intervention is whether it is advisable to leave an interatrial communication to facilitate baffle dilation or stent placement. In this case, we used the fossa ovalis (and in fact enlarged it), and therefore no interatrial communication was present, a feature that challenged the percutaneous approach.

This report illustrates a rare anatomic variant of scimitar syndrome and the technique used for repair. We highlight key principles reconciling challenging anatomies to be considered for future complex partially anonymous pulmonary venous anatomies.