1 Introduction

Aorta–right atrial tunnel (ARAT) is a rare congenital cardiovascular malformation first described by Otero Coto et al. [1] in 1980. It is characterized by an abnormal blood vessel from the aortic sinus connecting to the right atrium, forming a left-to-right shunt [2]. ARAT can exist alone or be associated with other congenital heart malformations. Because of the left-to-right shunt, which increases pulmonary blood flow and pulmonary artery pressure, patients with ARAT often exhibit dyspnea, cyanosis, and heart failure; infectious endocarditis and embolism are also possible. Therefore, timely diagnosis and treatment are important.

ARAT is most commonly diagnosed using echocardiography. However, echocardiography has limitations in accurately showing the tunnel's location and shape, especially when other complex malformations are also present. By contrast, multislice computed tomography (MSCT) generates high-resolution images, allowing for three-dimensional reconstructions and postprocessing methods to analyze the anatomy. As a result, it is superior to echocardiography for demonstrating the tunnel's points of terminus, direction, and adjacent structures. Additionally, MSCT is faster than magnetic resonance imaging (MRI) and associated with less metal artifact interference.

We report a 1-month-old female infant who was diagnosed with ARAT in conjunction with an atrial septal defect and patent ductus arteriosus using low-dose MSCT. In contrast to previous echocardiography examinations that failed to achieve an accurate diagnosis of ARAT, MSCT not only precisely identified ARAT but also clearly delineated the structural characteristics of the conduit, including its anatomical origin and termination points.

2 Case Presentation

A previously healthy 1-month-old female infant with an unremarkable medical and family history presented with moaning, spitting, and dyspnea. Her vital signs were as follows: body temperature, 36.4°C; respiratory rate, 56/min; and heart rate, 177/min. Physical examination demonstrated cyanosis of the lips and a grade 6 systolic murmur in the third intercostal space at the right margin of the sternum. The triple concave sign was positive. Echocardiography showed partial anomalous pulmonary venous drainage, a patent ductus arteriosus, pulmonary hypertension, and an atrial septal defect. Low-dose CT was then performed using a SOMATOM Force scanner (Siemens, Munich, Germany) with the following parameters: tube voltage, 70 kV; tube current, 56/624 mAs/ref.; matrix size, 512 × 512; pitch, 0.98; rotation time, 0.25 s; collimation, 2 × 192 × 0.6; and slice thickness, 0.6 mm. The scan range extended from the thoracic inlet to 3 cm below the diaphragm. Prospective electrocardiography gating was used. The area of interest was set at the ascending aorta with a threshold value of 100 HU. Iohexol was used as a contrast agent (350 mg/mL; total volume, 6.6 mL; flow rate, 2.0 mL/s). The dose-length product was 19.5 mGy-cm and the effective radiation dose was 0.507 mSv.

Three-dimensional imaging showed a tubular connection between the right atrium and the aorta with a maximum diameter of 10 mm and a length of 33 mm. The connection opened into the left wall of the ascending aorta. A vascular structure migrated to the right and entered the right atrium, clearly showing the relationship between the tunnel and the coronary artery (Figure 1). The comprehensive diagnosis was ARAT in conjunction with an atrial septal defect, patent ductus arteriosus, and pulmonary hypertension. The patient underwent surgery to close the abnormal cardiac passage. After surgery, her diastolic and systolic cardiac function returned to normal, and her dyspnea disappeared. Only mild tricuspid regurgitation was notable on postoperative imaging. At her 3-month follow-up visit, she appeared healthy.

3 Discussion

ARAT is a rare congenital cardiac malformation of unknown cause characterized by an abnormal tunnel-like connection between the aorta and the right atrium [2]. Gajjar et al. [3] suggested that ARAT may be attributed to the abnormal development of elastic fibers in the aortic media and the weakening of the vascular wall, which gradually expands to form a tube between the high-pressure aorta and the adjacent low-pressure right atrium. In our patient, the characteristics of cardiac blood flow were complicated. Low-dose CT confirmed the existence of three left-to-right shunts: ARAT, patent ductus arteriosus, and atrial septal defect. In addition, it demonstrated the relationship between ARAT and the coronary artery.

Left-to-right shunts can easily result in pulmonary infection, Eisenmenger syndrome, heart failure, and infectious endocarditis. Our patient exhibited signs of pulmonary hypertension and had an enlarged right atrium and ventricle. Surgery should be performed as soon as possible to correct left-to-right shunts. The relationship between ARAT and the coronary artery also plays an important role in planning treatment [4].

Echocardiography is commonly performed to diagnose congenital heart disease owing to its noninvasive nature, low cost, and lack of radiation exposure. However, accurate assessment of ARAT can be challenging because of patient cooperation problems, complex blood flow, operator experience, and technical variations among operators. Although other diagnostic methods, including transesophageal echocardiography, cardiac angiography, and cardiac MRI, are options, each method has its own set of challenges, especially in pediatric patients. Transesophageal echocardiography can be uncomfortable for pediatric patients and requires a certain level of cooperation. Angiography is invasive and associated with risks that are not an issue with noninvasive diagnostic techniques. Cardiac MRI, although capable of displaying more subtle structures, can be time consuming and requires the patient to remain still for an extended period, which can be difficult for infants and children.

MSCT is noninvasive, has high resolution, provides the ability to create three-dimensional reconstructions, and allows for various postprocessing methods. Unlike echocardiography, it can show ARAT anatomy in considerable detail. In our patient, low-dose MSCT was able to show ARAT, a patent ductus arteriosus, and an atrial septal defect. Certain structural anomalies are challenging to clearly visualize on echocardiography. Furthermore, low-dose MSCT provided information about the tunnel's opening, shape, and surrounding structures; the postprocessed images clearly highlighted ARAT (Figure 2). Moreover, MSCT scanning is rapid and can be synchronized with breathing and heart rate. However, MSCT has certain shortcomings, such as the need for injection of intravenous contrast, radiation exposure, and artifacts generated by breathing and movement. To reduce the radiation dose by up to 50%, low-dose scanning techniques may be used, such as reducing tube current and voltage. These techniques still provide high-quality images. In addition, advanced iterative reconstruction algorithms can improve image quality at low radiation doses, reducing noise and artifacts. For uncooperative pediatric patients, sedation can reduce movement artifact. The use of respiratory gating techniques and rapid scanning modes can synchronize the respiratory cycle with the scan to reduce respiratory motion artifact and obtain clear images. Therefore, when performing MSCT in infants and young children, a combination of the above techniques should be used. Using low-dose MSCT and other diagnostic methods not only helps to clarify the diagnosis, but also provides an important reference for treatment and prognostication.

ARAT is classified as either posterior, in which the tunnel extends from the left aortic sinus to the posterior aspect of the aortic root, or anterior, in which it extends from the anterior aspect of the right aortic sinus to the right side of the aortic root [3]. MSCT not only aids in ARAT classification, but also allows more precise preoperative surgical planning by enabling an accurate assessment of the anatomy and the relationship between the coronary artery ostia and the aortic end of the tunnel. Other diagnostic examinations, such as transesophageal and transthoracic echocardiography, cannot provide this.

In summary, when complex cardiac structural abnormalities cannot be clearly defined on echocardiography and other examinations, MSCT is an excellent alternative. It can clearly demonstrate an ARAT's starting point, diameter, length, and relationship with surrounding coronary arteries. Additionally, three-dimensional reconstruction can comprehensively display the tunnel in great detail, helping patients clearly understand their pathology and assisting clinicians with formulating treatment and assessing prognosis.

Author Contributions

Bo Wang: conceptualization (equal), data curation (equal), investigation (equal), formal analysis (equal), methodology (equal), visualization (equal), writing–original draft (equal). Rongpin Wang: conceptualization (equal), funding acquisition (equal), supervision (equal), project administration (equal), writing–review and editing (equal).

Ethics Statement

The authors have nothing to report.

Consent

The patient's parents provided written consent for the publication of any potentially identifiable images or data included in this article.

Conflicts of Interest

The authors declare no conflicts of interest.