Variants and anomalies of the aortic arch (AA) are relatively common. In its standard configuration, the AA is left-sided and gives rise to three branches: the right brachiocephalic artery, the left common carotid artery, and the left subclavian artery (1, 2). Among the various AA variants, the most frequent is the brachiocephalic trunk, where the brachiocephalic and left common carotid arteries share a common origin. Another notable variant is the direct aortic origin of the left vertebral artery. Common AA anomalies include a left-sided arch with an aberrant right subclavian artery, a right-sided arch, and a double AA (3).

Interrupted aortic arch (IAA) is regarded as one of the most severe forms of AA anomalies. While AA anomalies typically involve variations in the branching patterns or the anatomical positioning of the AA, IAA is a rare congenital cardiovascular malformation characterized by a complete luminal discontinuity of the AA, resulting in the absence of the regular aortic continuity between the ascending and descending aorta (4), distinguishing it from severe coarctation and aortic atresia (5). This interruption disrupts the direct flow of oxygenated blood from the heart to the lower body, necessitating collateral circulation through alternative vessels, such as the patent ductus arteriosus (PDA), to maintain perfusion, especially for lower extremity blood flow (6).

IAA is a rare condition, representing only 1% of congenital heart diseases, which is frequently associated with additional congenital cardiac anomalies, including ventricular septal defects and PDA, further complicating the clinical presentation (7). While the precise causes of IAA are still unclear, it is generally regarded as a phenotype arising from diverse aetiologies (8). For example, around 50%–80% of individuals with type B IAA have genetic origins, including DiGeorge syndrome and chromosome 22q11 deletion, with the deleted region being linked to cardiovascular development derived from the neural crest (8, 9).

Celoria and Patton have classified IAA into three types based on the site of aortic interruption concerning the arch vessels (10): •

Type A, where the interruption occurs at the isthmus between the left subclavian artery and the ductus;

Echocardiography alone can provide an accurate anatomical diagnosis of an IAA. It should identify the site of the interruption and measure the length of the arch discontinuity, the narrowest dimension of the left ventricular outflow tract, the diameter of the aortic annulus, and the ascending aorta. Additionally, it should define the location of any associated ventricular septal defect, assess the presence of the thymus (as its absence may indicate DiGeorge syndrome), and evaluate the presence and size of any associated atrial septal defect (11). Furthermore, Doppler ultrasonography can assess functional changes in vascular and surrounding structures (14).

Computed tomography angiography (CTA) serves as a valuable complementary diagnostic tool for unstable patients with IAA in urgent situations (15). The benefits of multislice CT, such as rapid scanning, which minimizes the need for sedation or general anesthesia, high spatial resolution, and the ability to assess both the airway and lungs simultaneously, have made it an effective method for evaluating a range of congenital heart diseases (16, 17). CT demonstrates 98% accuracy in diagnosing specific cardiovascular anomalies compared to a clinical consensus diagnosis, including surgical findings as the reference standard. Following an initial echocardiographic evaluation, CT could potentially replace diagnostic cardiac catheterization for detailed anatomical clarification in neonates (18).

Along with identifying the location of the interruption, both echocardiography and CTA should provide measurements of the length of the arch discontinuity, as well as the diameter of the ascending aorta (11). This is essential because an end-to-end (19) or end-to-side (20) anastomosis between the ascending and descending thoracic aorta is performed during a one-stage repair of IAA. Additionally, if patients have a severely hypoplastic ascending aorta (diameter <3 mm), homograft patch augmentation of the ascending aorta must be performed (21) or may lead to left ventricular outflow tract obstruction, which can significantly complicate patient management (22).

In cases of IAA, accurate delineation and identification of associated cardiac pathologies are crucial for effective preoperative decision-making (23). This study aims to perform a comparative analysis of echocardiography and CTA in assessing thoracic findings in patients with IAA.

Our study compared the diagnostic accuracy of echocardiography and CTA for IAA.

IAA is a life-threatening condition with an absence of direct continuous blood supply to the lower body caused by a missing portion of the AA (25), which is accompanied by many cardiovascular anomalies, including PDA, ventricular and atrial septal defects, patent foramen ovale, hypoplastic ascending aorta, etc., as demonstrated in our study on Table 3. Each of these heart defects affects the course of the operation and the patient's further prognosis. Consequently, there is an increasing need for accurate radiological measurements and a comprehensive understanding of the lesion's anatomy during preoperative preparation (26).

The primary goal of surgical treatment for IAA is to restore normal blood flow by correcting the arch and associated cardiovascular defects. Prior to 2000, the standard surgical approach for IAA was staged repair. However, after 2001, it shifted to primary complete repair during the neonatal period (27), even with the complex intracardiac anomaly (28). This approach minimizes the need for multiple surgeries and improves long-term outcomes (29). Surgical intervention is essential for patient survival, as untreated IAA leads to a 90% mortality rate by a median age of 4 days (20).

The single-stage repair of IAA involves a direct anastomosis between the ascending and descending aorta after extensive mobilization. Since the procedure has become the approach of choice, the ascending aorta diameter is essential for surgical planning (30, 31), and many research findings emphasized the implication of ascending aorta measurements in cases of IAA. For instance, Schreiber et al. suggested that mobilizing the ascending aorta sufficiently would minimize tension around the anastomosis and reduce the risk of restenosis after one-stage primary correction (32). Furthermore, Kaulitz et al. revealed through echocardiographic measurements that the diameter of the ascending aorta was even related to the number of vessels originating from the proximal AA, indicating a connection to the type of IAA (33).

Among accompanying cardiovascular findings, hypoplasia of the ascending aorta is common in patients with IAA; in our sample, there are 34.5%. A more significant prevalence was reported by Vogel et al., who indicated, based on fetal echocardiographic data, a smaller-than-normal diameter of the ascending aorta in 73% of liveborn patients with IAA (34).

As for the measurement of the ascending aorta diameter, no statistically significant difference was observed between the echocardiography and CT in our sample. Blondheim et al. reported similar findings, showing a strong correlation between CT and echocardiographic measurements at various points along the ascending aorta, with the average measurement differences among their patients being clinically negligible (35). Similar results were revealed by the research of Tamborini et al., which concluded that in a cohort of patients with documented aortic dilatation or aneurysms, echocardiographic measurements of the proximal and ascending aorta demonstrated a strong correlation with CT measurements. These findings were characterized by minimal standard errors in the estimates and relatively low variability between and within observers (36).

Of the two imaging modalities used in our study, echocardiography is commonly employed as the initial imaging method, particularly for pediatric patients with IAA (Figure 1). However, since it is operator-dependent, it poses challenges when evaluating complex arch anomalies (12). In contrast, multislice CT offers high-resolution 3D imaging of IAA and collateral vessels. Combined with echocardiography, which detects intracardiac lesions, it typically provides enough information for preoperative planning in most cases (37). Recent advances in imaging modalities have improved accuracy and reliability (14), as evidenced by the lack of statistically significant differences between echocardiogram and CT measurements of ascending aorta diameter in our study.

In our study, CTA exceeded echocardiography in delineating IAA, exhibiting greater sensitivity and aligning closely with the findings of Al-Azzazy et al. (38). Their study reported a 100% sensitivity for CTA in diagnosing extracardiac aortic anomalies, surpassing the 92% sensitivity of Doppler echocardiography. Similar results were revealed by Soleimantabar et al., with the sensitivity and specificity of transthoracic echocardiography for detecting IAA at 75% and 100%, respectively, compared to CTA (39).

CTA provides a detailed visualization of AA anatomy and its spatial relationships with adjacent organs. Its advantage is further enhanced by various post-processing techniques, such as volume rendering, maximum intensity projection, and multiplanar reformatting, which can be applied to all structures within the scanned volume, making it superior to other imaging modalities for evaluating AA anomalies (5) (Figures 2, 3). Also, CTA is widely utilized for proper treatment and follow-up, as well as for preventing morbidities and mortalities (40). Traditionally, CT scans have been associated with high radiation exposure; however, recent advancements in radiation dose reduction technologies have significantly lowered the levels of exposure (41).

Table 4 compares echocardiography and CTA in diagnosing IAA, highlighting advantages and disadvantages. As demonstrated, echocardiography has multiple benefits, including availability and non-invasiveness, while CTA has disadvantages, such as radiation exposure and contrast-related issues. However, the critical advantage of CTA over echocardiography that makes it the method of choice is a comprehensive view of the AA and associated branches, including the precise location of the interruption, which is ideal for surgical planning.

In addition to echocardiography and CTA, magnetic resonance imaging is a highly effective multiplanar imaging technique that allows AA malformations to be assessed without exposing patients to radiation. Both black blood and bright blood sequences, which do not require contrast, as well as contrast-enhanced magnetic resonance angiography, can be utilized and are synchronized with the cardiac cycle to minimize motion artifacts (42). It is also a practical option, but is more costly, time-consuming, and still more prone to artifacts compared to multislice CT (37).

While both imaging modalities, echocardiography and CTA, play crucial roles in diagnosis, treatment planning, and follow-up, CTA has demonstrated superior sensitivity and comprehensive anatomical detail. Understanding the complementary roles of these tools can optimize clinical outcomes by guiding accurate diagnosis and appropriate interventions.

This study has several limitations that should be acknowledged. First, its retrospective design limits control over confounding variables and introduces potential selection bias, which may affect the generalizability of the findings. Second, the relatively small sample size (n = 58) reduces the statistical power, particularly for subgroup analyses. For instance, the lack of a statistically significant difference in ascending aorta diameter measurements between echocardiography and CTA may be attributable to insufficient sample size, as suggested by the elevated p-value. Furthermore, not all patients underwent all imaging modalities, limiting the ability to perform direct modality comparisons, such as between CTA and other cross-sectional imaging modalities, such as magnetic resonance imaging. These constraints highlight the need for larger, prospective studies to further validate and expand upon the present findings.

These findings indicate that echocardiography is a practical initial diagnostic tool. Recent advances in medical imaging have enhanced its capabilities, making it comparable to CTA in measuring specific anatomical features, such as the diameter of the ascending aorta. However, CTA offers superior accuracy and should be prioritized when echocardiographic results are inconclusive or when detailed anatomical information is critical for diagnosis and surgical planning. Expanding future research to include additional imaging modalities and a larger sample size could significantly enhance our understanding of IAA visualization.