Cor-Triatriatum Variant: Uncommon Cause of Unilateral Pulmonary Venous Hypertension

Megha M. Sheth DMRD, Dinesh L. Patel MD, Milin N. Garachh DMRD
U.N. Mehta Institute of Cardiology and Research Centre, Ahmedabad, Gujarat, India. 

Clinical History

A 32-year-old female, with no known co-morbidities, presented with complaints of recurrent haemoptysis, chest pain and dry cough for the past four months. Chest radiograph demonstrated diffuse reticulo-nodular opacities in the right lung parenchyma. Computed tomography (CT) of the thorax with contrast done at an outside hospital showed a non-enhancing hypodense filling defect in right half of the left atrium (LA) concerning for a mass. Small diameter of the right pulmonary artery (RPA) was noted with suspicious small atrial septal defect (ASD). Changes of pulmonary edema in form of smooth septal thickening with mild bronchiectatic changes with loss of right lung volume were also noted (Figure 1). 

Figure 1. CT thorax with contrast axial images showing volume loss and smooth interstitial septal thickening in right lung field (A) and hypodense lesion (arrow) within the right side of the LA chamber (B). Also noted a small calcified foci in a possible membrane within the LA.

Transthoracic echocardiogram (TTE) revealed cystic structure with internal echogenicity in the roof of the LA with possibility of pericardial cyst or hydatid cyst or mass considered.  The TTE also showed normal left ventricle (LV) chamber size, normal systolic function (left ventricular ejection fraction (LVEF) 55%), and normal LV compliance. Blood tests were unremarkable for any infection. Cardiovascular magnetic resonance (CMR) was advised for further evaluation of the left atrial mass.

CMR Findings

Contrast-enhanced CMR was performed on a 3T Vida (Siemens Healthineers, Erlangen Germany) scanner. T2 weighted (T2w) half-Fourier single shot turbo spin echo (HASTE) showed relative volume loss of the right hemithorax with peri-bronchovascular interstitial thickening in the right lung parenchyma (Figure 2). The LA was divided by a thin membrane into two chambers suggestive of cor-triatriatum variant (Figures 2 and 3, Movie 1). The left pulmonary veins (PV) drained into the left-sided LA chamber, communicating with the LV (Figure 3, Movie 1), while the right PV drained into an accessory right-sided LA chamber. The RPA and right PV appeared hypoplastic as compared to the left pulmonary artery and left PV. A hypointense lesion was noted in the accessory LA chamber causing its significant luminal compromise (Figure 3, Movie 1).

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Figure 2. Axial T2w HASTE (A), T1 weighted (T1w) Volumetric Interpolated Breath-hold Examination (VIBE) (B), and T2w short axis double inversion recovery with fat saturation (C) shows relative volume loss of the right hemithorax with peri-bronchovascular interstitial thickening in the right lung parenchyma (A). The LA is divided by a thin membrane into two chambers suggestive of cor-triatriatum variant (A, B). The lesion is hyperintense on both T1w and T2w images (A-C).

Figure 3. Four chamber cine balanced steady state free precession (bSSFP) at end-diastole showing the thin membrane (blue arrow) dividing the LA into two chambers, suggestive of cor-triatriatum variant.

Movie 1. Four chamber cine bSSFP stack showing the membrane within the LA separating it into right and left sided chambers and also the thrombus within the right sided LA chamber.

The lesion was hyperintense on both T1w and T2w images (Figure 2 and 4). The lesion did not show any significant elevated values on native T1 maps compared to myocardium (values 1016 to 1038 ms) (Figure 5). On first pass perfusion imaging and late gadolinium images with high TI, the lesion did not show any enhancement, consistent with a thrombus (Figures 5 and 6, Movie 2). Also noted on first pass perfusion was delayed filling of the right-sided LA chamber in comparison to the left-sided LA chamber suggestive of obstructed flow in the right pulmonary vasculature. The lung parenchymal findings were also consistent with unilateral pulmonary venous hypertension (Figure 1). 

Figure 4. T1w post contrast axial images, VIBE sequence (water only) showing the hypointense lesion in the LA.

Figure 5. Native T1 maps short axis, pre (A) and post (B) contrast images of the LA mass. Native T1 mapping values pre contrast ranged from 1016 to 1038 ms. On post contrast T1 maps, the lesion did not show any enhancement, hence appearing bright.

Figure 6. Late gadolinium enhancement four chamber view with high inversion recovery (A), and short axis images (B, C) with high inversion recovery (B) and perfusion sequence (C). The mass in the LA (arrows) is hypointense on all sequences, consistent with thrombus.

Movie 2. Short axis perfusion stack sequence showing the non-enhancing mass in the LA. There is delayed contrast uptake in the right sided accessory LA chamber.

Conclusion

Thus on CMR, the findings were cor-triatriatum sinister with right sided PV draining into the right sided LA chamber. A pre-existing congenital obstruction to the right-sided pulmonary venous drainage led to sluggish flow, predisposing to thrombus formation within the right-sided accessory LA chamber and secondary worsening of unilateral pulmonary venous hypertension. The patient was treated medically for acute pulmonary edema with diuretics and anticoagulants for the thrombus. Surgical intervention, mass excision with cor-triatriatum repair, was recommended but declined by the patient.

Quantification of differential branch pulmonary artery flows using phase-contrast CMR was not performed. In the setting of severe unilateral pulmonary venous obstruction and a hypoplastic RPA, phase-contrast CMR would have demonstrated differential diminished flow to the right lung. Omitting this measurement meant we could not quantify the physiological severity of the obstruction.

Perspective

Cor triatriatum is a rare congenital anomaly that is estimated to be present in 0.4% of patients with congenital heart disease (CHD).[1] It can occur in isolation but often is associated with other CHD, most commonly ASD and anomalous pulmonary venous connection.[2] Many early case series describe the presentation to be similar to mitral stenosis, with symptoms of dyspnea, signs of heart failure, and imaging consistent with pulmonary edema. The extent and orientation of the LA membrane can be quite variable, and pathologic study demonstrates that while described as a “membrane,” the tissue in fact contains cardiac muscle covered by fibrous endocardium.[3]

Cor triatriatum results from derangement of total incorporation of the common pulmonary vein into the LA. The pathological finding is a membrane that divides the LA into two chambers: a proximal one that receives normally formed PVs and a distal one that includes appendage and mitral vestibule.[4,5] A comprehensive classification of cor-triatriatum has been provided by Lucas (Table 1, Figure 7).[5,6] This patient was consistent with a Lucas classification C1a (Figure 7).

Figure 7. Lucas’ classification of cor triatriatum graphically illustrated. The labels of each heart correspond to the descriptions given in Table 1. AC = accessory chamber; IVC = inferior vena cava; LA = left atrium; LIV = left innominate vein; LPV = left pulmonary vein; LV = left ventricle; RA = right atrium; RPV = right pulmonary vein; RV = right ventricle; SVC = superior vena cava; VV = vertical vein.

Cor triatriatum is typically diagnosed by TTE, but other modalities such as CT and CMR are also used. A study compared CMR, TTE, and catheterization angiography in evaluating pulmonary venous anomalies, which included cases of cor triatriatum sinister.  CMR had a higher detection rate of 95%, compared to 69% for angiography and 38% for TTE.[7] Computed tomography angiography (CTA) is preferred over cardiac catheterization due to it being noninvasive and providing detailed anatomy. CMR is used to evaluate hemodynamics, valve disease, and chamber size and function.[7] CMR is considered the most reliable method for measuring the size and function of heart chambers. It can be helpful in assessing whether there is an excess load on the right ventricle. Additionally, it can identify the presence of blood clots in the accessory chamber (due to slow blood flow) or rule out the possibility of malignancy.[8]

Cor-triatriatum variants with divided pulmonary venous drainage are extremely rare and uncommon cause of unilateral pulmonary venous hypertension.[9] Furthermore, severe stasis within the congenitally partitioned LA chamber creates a prothrombotic environment; secondary thrombus formation may further compromise the restrictive orifice, exacerbating pre-existing pulmonary venous hypertension. The signs and symptoms are often non-specific, with imaging playing a crucial role in the diagnosis and exact anatomical delineation. Timely identification is crucial as surgical correction provides excellent long-term results in most of the cases.[10] Even in scenarios where patients elect to pursue conservative medical management, over surgical intervention, the comprehensive functional mapping provided by CMR is essential for tailoring pharmacological therapy and monitoring disease progression safely.[11] 

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References

1. Fuchs MM, Connolly HM, Said SM, Egbe AC. Outcomes in patients with cor triatriatum sinister. Congenit Heart Dis. 2018 Jul;13(4):628-632.
2. Nassar PN, Hamdan RH. Cor Triatriatum Sinistrum: Classification and Imaging Modalities. Eur J Cardiovasc Med. 2011 Jan;1(3):84-87.
3. Niwayama G. Cor triatriatum. Am Heart J. 1960;59:291–317.
4. Villa E, Le Bret E, Batisse A, Vouhé P. Obstructed right pulmonary venous drainage and ipsilateral lung hypoplasia. Eur J Cardiothorac Surg. 2004 May;25(5):899-901.
5. Herlong JR, Jaggers JJ, Ungerleider RM. Congenital Heart Surgery Nomenclature and Database Project: pulmonary venous anomalies. Ann Thorac Surg. 2000 Apr;69(4 Suppl):S56-69.
6. Krabill KA, Lucas RV. Abnormal pulmonary venous connections. In: Emmanoulides GC, Riemenschneider TA, Allen HD, Gutgesselle, eds. Heart disease in infants, children, and adolescents including the fetus and young adult. Baltimore: Williams and Wilkins, 1995:838–74.
7. Masui T, Seelos KC, Kersting-Sommerhoff BA, Higgins CB. Abnormalities of the pulmonary veins: evaluation with MR imaging and comparison with cardiac angiography and echocardiography. Radiology. 1991 Dec;181(3):645-9.
8. von Bartheld B, Rijnierse M, van Loon R, Meijboom L. A rare case of partial cor triatriatum diagnosed at an adult age: a case report. Eur Heart J Case Rep. 2023 Feb 13;7(3):ytad082.
9. Ehrich DA, Vieweg WV, Alpert JS, Folkerth TL, Hagan AD. Cor triatriatum: report of a case in a young adult with special reference to the echocardiographic features and etiology of the systolic murmur. Am Heart J. 1977 Aug;94(2):217-21.
10. Jaswal V, Rana P, Bansal V, Gourav KP, Sharma A, Thingnam SKS. A six-chambered heart: cor triatriatum sinister with double-chambered right ventricle in association with ventricular septal defect. Egypt Heart J. 2022 Feb 16;74(1):10.
11. Buchori E, Dewi DK, Hilman, Adityabiantoro P. Cardiac MR imaging of cor triatriatum sinister in an elderly man: A rare case report. Radiol Case Rep. 2024 Jan 20;19(4):1468-1471.

Case prepared by:
Jason N. Johnson, MD MH
Editor-in-Chief, Cases of SCMR
Le Bonheur Children’s Hospital, The University of Tennessee Health Sciences, St. Jude Children’s Research Hospital