Graphical abstract
Highlights
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CTS in HLHS can masquerade as an atrial septum.
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T-cor and L-cor are a spectrum of CTS.
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Prenatal assessment of LA morphology can assist with diagnosis of this high-risk entity.
Introduction
Cor triatriatum sinister (CTS) in hypoplastic left heart syndrome (HLHS) is a rare congenital condition in which the left atrium (LA) is divided by a membrane into a posterosuperior and anteroinferior chamber. In typical CTS (T-cor), the posterosuperior chamber typically receives the pulmonary venous return and the anteroinferior chamber communicates through the mitral valve (MV) to the left ventricle. Hypoplastic left heart syndrome is a condition where the left side of the heart is underdeveloped, and CTS can further complicate the condition, leading to pulmonary venous obstruction and increased mortality. A small subset of patients with T-cor in HLHS have been described as having unusually small LAs with complex membranous folds. This subset of T-cor with a diminutive LA has been named labyrinthine-cor (L-cor) in the first study describing the prevalence of this subset in fetal patients with HLHS.1 These patients with L-cor and T-cor in HLHS can have either restrictive atrial septum (RAS) or unrestricted physiology based on the pulmonary venous Doppler antegrade/retrograde velocity-time integral (VTI) ratio or atrial septal mean gradients.2
Our goal is to raise awareness that T-cor and L-cor represent a spectrum of CTS in HLHS fetuses. We aim for this article to encourage fetal cardiologists to consider and recognize this entity prenatally. Early recognition of this condition can aid in risk stratification and caution for cardiac catheterization-based prenatal and postnatal atrial septal intervention planning, postnatal surgical approach, prognostication, and counseling.
Case Presentation
Case 1
We present a case of a 31-year-old mother who initially presented to fetal clinic at 26 5/7 weeks gestation. Cell free DNA testing was consistent with low risk for trisomy. Prenatal diagnosis was consistent with HLHS with mitral atresia and aortic atresia subtype. Two pulmonary veins (PVs) were seen draining into the left atrial cavity with an unobstructed Doppler pattern. The LA was diminutive and difficult to discern in fetal echocardiography (Video 1, Figures 1 and 2A). The PV VTI ratio did not suggest any restriction, and based on color-flow Doppler, there was unobstructed flow into the LA (Video 2, Figure 2). The infant was delivered at 38 4/7 weeks' gestation with a birth weight of 3,070 grams. On the initial postnatal echocardiogram, the infant was noted to have a diminutive LA and an unrestrictive flow across the atrial septal connection. Three PVs were seen connecting to the superior part of the LA. The atrial septum was posterosuperiorly deviated with a tunnel-like patent foramen ovale (PFO) seen superiorly with a prominent coronary sinus (Video 3). There appeared to be tiny fenestrations within the perceived atrial septum (Video 3). After delivery, oxygen saturations were 88% to 94%, and the patient appeared stable on room air. No catheter-based interventions were performed due to adequate saturations on room air, appearance of “unrestricted” shunting into the right atrium (RA), and overall well appearance.
Figure 1.
Case 1. Fetal two-dimensional echocardiogram without (A and C) and with (B and D) simultaneous color-flow Doppler in diastole (A and B) and systole (C and D), demonstrates HLHS with a diminutive LA that appears crowded with possible fenestrated atrial septum raising suspicion for L-cor.
Figure 2.
Case 1. (A) Fetal two-dimensional echocardiogram without (left) and with (right) simultaneous color-flow Doppler, modified sagittal bicaval systolic view, demonstrates 2 PVs draining into the posterior diminutive LA with left-to-right shunting across the superior PFO. (B) Fetal two-dimensional guided pulsed-wave Doppler spectral display demonstrates the pulmonary venous Doppler profile with no retrograde flow, consistent with unobstructed atrial septum and pulmonary venous flow pattern. L-cor is visualized within the diminutive LA. AS, Atrial septum; PA, pulmonary artery; RV, right ventricle; SVC, superior vena cava.
In the operating room (OR), the atrial septum was described as essentially intact with very little egress from the LA to the RA. The left atrial cavity was diminutive with the PVs communicating via a small pathway to the LA. The patient underwent stage 1 palliation including Norwood procedure and a modified Blalock–Taussig shunt. The pulmonary venous confluence was marsupialized with a bovine pericardial patch that was attached at the RA and inferior vena caval junction and went across onto the left-sided PVs, creating a pulmonary venous connection to the RA (Figure 3). There were no significant complications with the surgery. Subsequently, the postoperative course was complicated by high-output chylous pleural effusions requiring thoracic duct ligation and diaphragm fenestration. The patient subsequently underwent multiple cardiac catheterizations to evaluate the PVs and marsupialization area that required stenting and balloon angioplasty of the PVs. After heart transplantation evaluation, the patient was deemed not to be a transplant candidate and the family elected palliative extubation.
Figure 3.
Case 1. The pulmonary venous confluence was marsupialized with a bovine pericardial patch that was attached at the RA and inferior vena caval junction and went across onto the left-sided PVs, creating a pulmonary venous connection to the RA. LLPV, Left lower PV; LV, left ventricle; LUPV, left upper PV; RLPV, right lower PV; RUPV, right upper PV; RV, right ventricle. Illustration courtesy of Yaeji Kim.
Case 2
Our second case is a 27-year-old primigravida who initially presented to fetal clinic at 25 4/7 weeks’ gestational age carrying a singleton fetus with HLHS with mitral stenosis and aortic stenosis subtype. Cell free DNA testing showed low risk for trisomy and 22q11 microdeletion syndrome. Amniocentesis was not performed due to parental preference. The atrial septum appeared fenestrated with a posterosuperiorly located PFO and an additional small fenestration with left-to-right shunting (Video 4, Figure 4A). Two PVs were seen entering the LA, and fetal echocardiograms since 32 4/7 weeks’ gestational age continued to show a borderline pulmonary venous antegrade/retrograde VTI ratio of 3 to 4 (Figure 4B). The LA was moderately hypoplastic but not diminutive (Video 5, Figure 5). There was prenatal concern for T-cor membrane within the left atrial cavity (Videos 4-6, Figures 4A, 5, and 6A). The fetus had other comorbidities including craniosynostosis, unilateral renal agenesis, and severe intrauterine growth restriction. Delivery was induced at 37 weeks 3/7 days due to severe intrauterine growth restriction. Prostaglandins were initiated to keep the patent ductus arteriosus open. Postnatal oxygen saturations ranged between 75% and 85%, requiring a fraction of inspired oxygen of 35% to 40%. Postnatal echocardiogram confirmed T-cor with PVs draining into the posterosuperior pulmonary venous chamber with egress through the PFO located superiorly and a small fenestration through the T-cor membrane into the anteroinferior chamber (Videos 7 and 8, Figure 6B). Birth weight of 1,900 g and other comorbidities precluded surgery as an option for atrial septectomy and resection of the membrane. Although a known high-risk intervention for this subset of patients, a percutaneous atrial septal stent placement procedure was attempted as a palliative measure in the cardiac catheterization lab with parental shared decision-making. Despite this effort to salvage the patient by allowing for egress across the RAS, the infant passed away.
Figure 4.
Case 2. (A) Fetal two-dimensional echocardiogram demonstrates possible fenestration of the atrial septum and a superior PFO with a curvilinear membrane in a moderately hypoplastic LA that is not diminutive, consistent with T-cor. (B) Fetal two-dimensional guided pulsed-wave Doppler spectral display demonstrates the pulmonary venous Doppler profile with antegrade/retrograde VTI ratio consistent with borderline atrial septal restriction.
Figure 5.
Case 2. Fetal two-dimensional echocardiogram, diastolic (A and B) and systolic (C and D) images without (A and C) and with (B and D) simultaneous color-flow Doppler, demonstrates a moderately hypoplastic LA that is not diminutive with a curvilinear membrane suggestive of T-cor, as well as left-to-right shunting across the PFO that is posterosuperiorly located.
Figure 6.
Case 2. (A) Fetal two-dimensional echocardiogram of a modified sagittal bicaval view demonstrates a dilated RA, moderately hypoplastic LA that is not diminutive, and a curvilinear T-cor membrane within the LA. (B) Postnatal two-dimensional TTE, systolic image without (left) and with (right) simultaneous color-flow Doppler, demonstrates a curvilinear T-cor membrane within the LA with the pulmonary venous egress across the foramen ovale located posterosuperiorly and a small fenestration seen in the membrane with minimal flow into the LA. PA, Pulmonary artery.
Discussion
The 2 patients described highlight a varied spectrum of CTS in HLHS. The first reported case series with L-cor was published after the birth of our patient.1 In case 1, the LA was unusually small and difficult to discern on fetal and postnatal echocardiogram. Based on imaging and clinical scenario, the atrial septum was not restrictive in fetal or postnatal life. However, since the atrial septum was described as intact in the OR as well as there being a concern for anomalous pulmonary venous connection, a marsupialization technique was performed (Figure 3) in our patient. The patient subsequently had a complicated postoperative course and did not survive.
Cor triatriatum membrane can be mistaken for an atrial septum in utero and on the initial echocardiograms, similar to our patient described in case 1. The outcomes of HLHS with RAS have remained suboptimal over the years.3 L-cor (Figure 7A) is an anatomical variant of T-cor (Figure 7B), leading to similar physiology that should be identified early in disease progression, such that operative procedures can be modified to achieve the best outcomes. There is a small pre-cor or pulmonary venous chamber that receives the PVs, multiple folds within the hypoplastic LA, and a post-cor chamber that drains into the hypoplastic or atretic MV. There can be multiple areas of shunting through small fenestrations in the membrane that allow the PVs to drain across the membrane to the RA via a dilated unroofed coronary sinus.1 This can be mistaken for and appear as a fenestrated atrial septum prenatally. The PVs are usually not fully seen by the surgeons in the OR due to the complex membranes. Additionally, recognition of the L-cor preoperatively may change the surgical approach. In general, atrial septectomy is performed via a cannulation site at the appendage, but if inspection and resection of the CTS membrane is expected, a separate atriotomy might be needed for better exposure. Prenatal diagnostic clues to identify T-cor or L-cor (Table 1) and further postnatal imaging techniques such as two-dimensional or three-dimensional TEE preoperatively might help the surgeon to visualize the membrane better.
Figure 7.
(A) Case 1 illustration of HLHS with diminutive LA and complex membranous folds representing L-cor dividing the LA into pre L-cor and post L-cor with multiple fenestrations within the L-cor membrane, some draining into the CS; PVs are shown draining into the pre-L-cor chamber and flow across the PFO into the RA. (B) Case 2 illustration of HLHS with moderately hypoplastic LA with a curvilinear membrane representing T-cor dividing the LA into pre-T-cor and post-T-cor with fenestrations within the T-cor membrane, some draining into the LA post-T-cor chamber; PVs are shown draining into the pre-T-cor chamber and flow across the PFO into the RA. LLPV, Left lower PV; LV, left ventricle; LUPV, left upper PV; RLPV, right lower PV; RUPV, right upper PV; RV, right ventricle. Illustrations courtesy of Yaeji Kim.
Table 1.
Fetal echo characteristics and clues to identify L-cor versus T-cor in HLHS
Our second case is a patient with HLHS and T-cor with a borderline RAS and provides additional clues to distinguish the presence of T-cor from L-cor during prenatal life. Case 2 was consistent with T-cor with moderately hypoplastic LA that was not diminutive. The multiple labyrinthine folds were not seen, and the curvilinear membrane that was visualized divided the LA into a posterosuperior pulmonary venous chamber and an anteroinferior chamber closer to the hypoplastic MV. Cor triatriatum sinister in HLHS was first described by Dr. Eidem and Dr. Cetta in 2001; they found a very small subset of patients with HLHS may have left atrial complexes with total anomalous pulmonary venous connections and membranous portions consistent with CTS.4 The variations of CTS, location of the PFO, and presence or absence of partial or total anomalous PVs can determine the initial postnatal presentation and can complicate cardiac catheterization-based atrial septal intervention.5,6
Catheter-based techniques are typically used when addressing patients with HLHS and RAS but may prove to be a challenge in patients with CTS in HLHS due to difficulty in discerning the position of the actual atrial septum and can have significant complications. In addition, the restriction in CTS may be through the multiple membranous folds and not at the level of the PFO alone, which makes the cardiac catheter-based option challenging. They may also not be candidates for prenatal atrial septal interventions, and hence the management of such patients may need to be tailored to the OR as opposed to the cardiac catheterization lab in case of concerns for RAS.1 Furthermore, multilevel obstruction to pulmonary venous return can also be present, making it more challenging. The presence of L-cor and T-cor in HLHS can lead to pulmonary venous obstruction and consequences similar to RAS. The use of VTI ratios can be helpful in fetal echocardiography for diagnosing and managing RAS. A VTI ratio >3.0 and <5.0 showed no difference in survival between patients with L-cor with or without restriction.1, 2, 3 The presence of L-cor with RAS in patients with HLHS is known to have increased mortality.1 Our first case suggests that the presence of L-cor without an RAS may also increase morbidity and mortality in patients with HLHS.
Both cases were unique in the appearance of the membrane and left atrial chamber sizes, but both patients had fenestrated-appearing atrial septum prenatally. The modified sagittal bicaval view with visualization of atrial inflow and outflow tracts in the fetal echocardiogram was helpful to look for the CTS membrane in both cases (Video 2, Video 6). Clues to consider the diagnosis for L-cor prenatally would be diminutive and crowded-appearing LA, multiple areas of atrial-level shunting (fenestrations) frequently with connections of the membrane to the coronary sinus, and the PVs communicating with the LA, distinguishing it from total anomalous pulmonary venous return.1 On the other hand, T-cor can be identified as a curvilinear membrane within the left atrial cavity and the LA may not be diminutive. Fenestrated-appearing atrial septum can be present in both spectrums. Prenatally, it is important to carefully assess the left atrial size, morphology, presence or absence of “crowding” of the LA, or a membrane within the LA in patients with HLHS. Early diagnosis of L-cor and T-cor on fetal echocardiography (Table 1) is vital for appropriate planning for postnatal interventions, to potentially guide the surgical approach and management strategies in this rare cohort to better understand the prognosis and to prepare the surgeons and the cardiovascular intensive care unit after birth.1,3,7,8
We suspect that the presence of a CTS membrane with or without membranous folds increases the risk of morbidity and mortality and is an important prognostic marker for patients with HLHS.6 The mortality and morbidity rates for T-cor in HLHS patients are not well established. In the largest study on the incidence of L-cor in HLHS to date, the study found the incidence of L-cor to be around 7.7% in patients with HLHS, and that 72.7% of patients with L-cor had RAS. These patients were more likely to have decompressing veins. The 1-year survival in patients with L-cor and RAS is only 25%.1,3 In addition, fetal lung magnetic resonance imaging findings of nutmeg lungs in fetuses with HLHS is an overall poor prognostic marker in the presence of pulmonary lymphangiectasia. This may also help risk stratify the cohort of fetuses with T-cor and L-cor to assess their overall prognosis.
In this case report, we have described the spectrum of CTS in HLHS fetuses. Larger, multicenter studies to compare the morbidity, mortality, and outcomes between T-cor and L-cor in HLHS can be challenging due to a low incidence of this rare entity, and hence case reports to help guide our understanding and tailor our counseling and management will be important.
Conclusion
T-cor and L-cor are rare anatomical variants in patients with HLHS and can masquerade as an atrial septum. Atrial septal interventions in the catheterization lab can have significant complications. The surgical approach may require a separate atriotomy to visualize the membrane. Careful assessment of the left atrial morphology should be included in the scanning protocol for all HLHS patients. Prenatal diagnosis is crucial for surgical planning and approach. We suspect that both spectrums of CTS, L-cor and T-cor, can increase the risk of morbidity and mortality and are an important prognostic marker for patients with HLHS.
Ethics Statement
The authors declare that the work described has been carried out in accordance with the following guidelines: Retrospective case series data collected from existing medical records. No new experiments were conducted.
Consent Statement
The authors declare that since this was a non-interventional, retrospective, observational study utilizing de-identified data, informed consent was not required from the patient under an IRB exemption status.
Funding
The authors declare that this report did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Disclosure Statement
The authors reported no actual or potential conflicts of interest relative to this document.
Acknowledgments
We thank Nathan Stecchi and Heather Perkins.
Footnotes
Supplementary data related to this article can be found at https://doi.org/10.1016/j.case.2025.08.004.
Supplementary Data
Case 1. Fetal two-dimensional echocardiogram without (left) and with (right) simultaneous color-flow Doppler demonstrates HLHS with a diminutive LA that appears crowded with a possible fenestrated atrial septum, raising suspicion for L-cor.
Case 1. Fetal two-dimensional echocardiogram without (left) and with (right) simultaneous color-flow Doppler, modified sagittal bicaval view, demonstrates 2 PVs draining into the posterior diminutive LA with left-to-right shunting across the superior PFO; L-cor is visualized within the diminutive LA. AS, Atrial septum; PA, pulmonary artery; RV, right ventricle; SVC, superior vena cava.
Case 1. Two-dimensional TTE without (left) and with (right) simultaneous color-flow Doppler, subcostal view, demonstrates the plane of the posterosuperiorly deviated atrial septum distinct from the fenestrated CTS membrane (sometimes mistaken as the atrial septum) with a superior PFO and a prominent coronary sinus.
Case 2. Fetal two-dimensional echocardiogram demonstrates possible fenestration of the atrial septum and a superior PFO with a curvilinear membrane in a moderately hypoplastic LA that is not diminutive, consistent with T-cor.
Case 2. Fetal two-dimensional echocardiogram without (left) and with (right) simultaneous color-flow Doppler, demonstrates a moderately hypoplastic, crowded LA that is not diminutive, but with a curvilinear membrane suggestive of T-cor, as well as left-to-right shunting across the PFO that is posterosuperiorly located.
Case 2. Fetal two-dimensional echocardiogram of a modified sagittal bicaval view demonstrates a dilated RA, moderately hypoplastic LA that is not diminutive and a curvilinear T-cor membrane within the LA. PA, Pulmonary artery; RV, right ventricle.
Case 2. Postnatal two-dimensional TTE, without (left) and with (right) simultaneous color-flow Doppler, demonstrates a curvilinear T-cor membrane within the LA with the pulmonary venous egress across the PFO located posterosuperiorly and a small fenestration seen in the membrane with minimal flow into the LA.
Case 2. Two-dimensional TEE without (left) and with (right) simultaneous color-flow Doppler, demonstrates a moderately hypoplastic LA, curvilinear T-cor membrane within the LA and the pulmonary venous egress through the PFO.
References
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Case 1. Fetal two-dimensional echocardiogram without (left) and with (right) simultaneous color-flow Doppler demonstrates HLHS with a diminutive LA that appears crowded with a possible fenestrated atrial septum, raising suspicion for L-cor.
Case 1. Fetal two-dimensional echocardiogram without (left) and with (right) simultaneous color-flow Doppler, modified sagittal bicaval view, demonstrates 2 PVs draining into the posterior diminutive LA with left-to-right shunting across the superior PFO; L-cor is visualized within the diminutive LA. AS, Atrial septum; PA, pulmonary artery; RV, right ventricle; SVC, superior vena cava.
Case 1. Two-dimensional TTE without (left) and with (right) simultaneous color-flow Doppler, subcostal view, demonstrates the plane of the posterosuperiorly deviated atrial septum distinct from the fenestrated CTS membrane (sometimes mistaken as the atrial septum) with a superior PFO and a prominent coronary sinus.
Case 2. Fetal two-dimensional echocardiogram demonstrates possible fenestration of the atrial septum and a superior PFO with a curvilinear membrane in a moderately hypoplastic LA that is not diminutive, consistent with T-cor.
Case 2. Fetal two-dimensional echocardiogram without (left) and with (right) simultaneous color-flow Doppler, demonstrates a moderately hypoplastic, crowded LA that is not diminutive, but with a curvilinear membrane suggestive of T-cor, as well as left-to-right shunting across the PFO that is posterosuperiorly located.
Case 2. Fetal two-dimensional echocardiogram of a modified sagittal bicaval view demonstrates a dilated RA, moderately hypoplastic LA that is not diminutive and a curvilinear T-cor membrane within the LA. PA, Pulmonary artery; RV, right ventricle.
Case 2. Postnatal two-dimensional TTE, without (left) and with (right) simultaneous color-flow Doppler, demonstrates a curvilinear T-cor membrane within the LA with the pulmonary venous egress across the PFO located posterosuperiorly and a small fenestration seen in the membrane with minimal flow into the LA.
Case 2. Two-dimensional TEE without (left) and with (right) simultaneous color-flow Doppler, demonstrates a moderately hypoplastic LA, curvilinear T-cor membrane within the LA and the pulmonary venous egress through the PFO.