IAA is a rare congenital cardiovascular malformation, accounting for 1% of the critical congenital heart diseases in children [11–13]. The incidence rate of IAA is about 0.19/1000 live births, accounting for 5% of the cases of aortic arch obstruction [14, 15]. The formation of IAA is related to chromosomal recombination and single gene abnormality .
The formation of IAA is related to chromosome recombination and single gene abnormality , which indicates an undeveloped, degenerated, and atrophic formation of the proximal segment or the fourth arch of the left dorsal aorta in the 6th to 7th week of an embryo. The continuity of the lumen between the aortic arch and the descending aorta is interrupted. IAA rarely occurs in isolation. About 95% of the IAA patients also presented other complex congenital heart diseases, such as ventricular septal defect and atrial septal defect. About 8% of the patients were not accompanied by other heart diseases. In this study, only 2 cases (8.00%) were not accompanied by other heart diseases, and the IAA patients accompanied with ventricular septal defect and patent ductus arteriosus (9 cases, 36%) were the most, which was basically close to the above study . IAA was first described in 1778, and has high mortality rate. Until the 1970s, with the emergence of prostaglandins and the improvement of surgical techniques, the complete repair of the neonatal period became normal [12–13]. In this study, 10 patients completed surgical treatment, and all patients survived.
4.1 Clinical features of IAA
The anatomical abnormality of IAA is often associated with patent ductus arteriosus and ventricular septal defect, also termed as IAA triad . The degree of collateral circulation in the chest, abdomen, and lower limbs supplied by the descending aorta is the key to the patients’ survival. When the patient’s collateral circulation maintains basic lower limb function, the blood perfusion in the descending aorta mainly depends on the pulmonary artery, and lower limb hypoperfusion or hypotension may occur, which can lead to electrolyte imbalance, renal insufficiency, multiple organ failure or circulatory failure, and finally cause the patient to die in the neonatal period . In this study, all adult patients had abundant collateral circulation. However, there were three patients in the study that were not supplied by the pulmonary artery, but were only supplied by the chest or abdominal artery collateral circulation. One case was a 56-year-old adult, and two cases were about 1-year-old child. The clinical manifestations of adult IAA are diverse, including asymptomatic, headache, hypertension, and differences in blood pressure between upper and lower limbs . As the aortic arch is interrupted, the pressure of the ascending aorta is increased, and the blood pressure of the patient's upper limbs is significantly higher than that of the lower limbs. Therefore, if it is found that the blood pressure of the patient's upper and lower limbs is inconsistent, in addition to dissection and vascular stenosis, the possibility of IAA should also be considered.
4.2 Classification characteristics of IAA
IAA is characterized by anatomical discontinuity between ascending and descending aorta that can be complete discontinuity or connected by residual fiber band but interferes with the blood flow. The most commonly used method in clinical practice is described by Fournier et al. . According to the different locations of disconnection, IAA is divided into the following three types: type A (accounting for 28%) is caused by the abnormal degeneration of the left fourth arch artery after the left subclavian artery rose to the normal position. In this study, 17 (68%) cases were type A, while Type B (70%) is the most common type. The aortic arch breaks between the left common carotid artery and the left subclavian artery orifice, which is related to 22q11.2 deletion. This is caused by abnormal degeneration of the left fourth arch artery in the early development before the migration of the anterior part of the left subclavian artery. Type C (< 5%) is rare, which is the interruption of the aortic arch between the brachiocephalic trunk and the opening of the left common carotid artery, caused by the abnormal degeneration of the left third and fourth arch arteries [20–21]. Compared to the study by Fournier et al., there are more patients presented type A in our study. This phenomenon could be attributed to the rare occurrence of IAA cases. Currently, there are no studies with a large dataset, and hence, there may be deviation. Therefore, more studies are required to improve the epidemic-related data of this disease. Arentje et al.  further divided IAA into 6 subtypes according to different sites of interruption and opening position of the right subclavian artery. However, the descending aorta originated from pulmonary artery. In their study, 35% of IAA were type A and 6% were type A1, while in our study, 15 (60%) cases of type A were severed at the distal end of the left subclavian artery orifice, and 5 (20%) cases of type B were located between the left common carotid artery and the left subclavian artery orifice, while in the study by Arentje et al., 53% were type B and 2 cases were type B1 (8%). The transection occurred between the left common carotid artery and the left subclavian artery opening, and the right subclavian artery originated from the descending aorta, while in the study of Arentje et al., 6% cases were type B1. In our study, it is rare that the type C is not observed clearly. It is located between the innominate artery and the left common carotid artery. Among them, 3 (12%) cases of the patients had an autologous circulation of the descending aorta, which could not be classified by the above classification method. Therefore, the author also classified according to the research of Wang et al. . Because the source of blood supply in the descending aorta is related to cyanosis, Wang et al. classified IAA into 5 types according to the analysis of disconnection position and blood supply of the descending aorta. In the present study, type A accounted for 60%, type B accounted for 28%, type C and type D accounted for 0%, and type E accounted for 8% cases, which is extremely rare. The severed part is located at the distal end of the opening of the left subclavian artery, and the descending aorta is supplied by the thoracic collateral branches. Among them, 1 (4.00%) case did not belong to the above classification. The interruption of the 1 case occurred between the left common carotid artery and the left subclavian artery opening, and the descending aorta is supplied by the thoracic collateral branch circulation (Fig. 3). Therefore, the author suggests adding a type G to the "two types and five types"(Fig. 3A) classified on the basis of cyanosis and non-cyanosis modified by Wang et al. , which is located between the opening of the left common carotid artery and left subclavian artery, and the descending aorta is supplied by thoracic collateral branches. These adjusted classification criteria are in agreement with the conventional classification of congenital heart disease and are more comprehensive than those described previously.
4.3 Value of DSCT in the diagnosis of IAA
Currently, the noninvasive imaging methods for the diagnosis of IAA mainly include computed tomography angiography (CTA), echocardiography, and cardiac magnetic resonance (MR), which basically replace the invasive digital subtraction angiography (DSA) examination . Ultrasound is the preferred method for diagnosing congenital heart disease. It is characterized by non-radiation, real-time dynamics, and multiple levels. However, due to the high position of the aortic arch, the observation of this position is easily restricted. It takes a long time to identify patients with IAA by cardiac MR, which is not conducive to screening patients. A previous study  reported that IAA is increased, as observed by CTA. Moreover, the anatomical continuity and separation between the aorta and the descending aorta were interrupted and separated. In some patients, strips of fiber could be observed. The ratio of ascending aorta diameter to descending main pulmonary artery diameter was abnormal, while the ascending aorta was widened, and the descending aorta was narrowed. The average value of our study was 1.27, indicating that the ascending aorta, descending aorta, and the ratio of ascending aorta/descending aorta of patients with type A and type B patients were significantly different. Furthermore, in our study, the pulmonary artery diameter of type A patients is larger than that of type B patients. The author speculate that it may be due to the pulmonary artery supplying the descending aorta and the left subclavian artery perfusion in type B patients. Therefore, the pulmonary artery needs more pressure in type B patients than that in type A patients who only have the descending aortic blood vessel, resulting in higher pulmonary artery pressure in type B patients, thus type A The patient's pulmonary artery has a wider inner diameter. There is no difference between of type A and type B patients among the left and right pulmonary artery diameters, the ratio of left pulmonary artery diameter to main pulmonary artery diameter and the ratio of right pulmonary artery diameter to main pulmonary artery diameter, as well as the ratio of left pulmonary artery diameter to right pulmonary artery diameter, which might be caused by abundant collateral circulation shunt. Some patients can also see that it is supplied by the collateral circulation of tortuous and thickened arteries. For example, the descending aorta is supplied by the intercostal artery, the celiac artery, the left hepatic artery, the internal iliac, and the external arteries. There are also several cases in our study.
DSCT's multi-planar reconstruction, VR and other three-dimensional reconstruction techniques can clearly determine the exact location of IAA and the relationship between adjacent blood vessels, and then determine the clinical classification and blood supply. In the study, it was found that sagittal imaging along the aortic arch is easier to show the location of the dissection. In addition, DSCT displays other congenital heart diseases and PDA shunt. DSCT combined with post-processing technology is used to design the operation path map for interventional therapy and evaluate the surgical effect . In the current study, 10 patients completed surgical treatment, and postoperative circulation recovered. Patients with IAA after repair require lifetime follow-up, mainly to monitor the left ventricular outflow tract obstruction and recurrent coarctation of aorta .
4.4 Treatment of IAA
Surgical reconstruction is the preferred treatment for IAA children. Immediate surgery is recommended if the hemodynamics are stable, and the postoperative effect is satisfactory, and although the reoperation rate is high, most children can survive for a prolonged period . Whether IAA adults need surgical treatment is controversial, which needs to be combined with the patient's condition . Because the adult patient survivors have abundant collateral circulation compensation, some patients can survive without surgery and can be treated conservatively.
4.5 Differential diagnosis of IAA
IAA should be differentiated from coarctation of the aorta (COA) and aortic arch thrombosis (AAT). COA refers to the local stenosis of the aortic cavity formed by the thickening of the inner wall of the aorta and the internal folding of the aortic wall tissue, but has a complete vascular wall . NAAT is relatively rare, and most children cannot survive. It is also important to pay attention to other diseases of the patient, such as sepsis, other thrombotic diseases, polycythemia, etc., but the thrombus can be partially absorbed after anticoagulation therapy .