A vascular ring is considered when a young child has symptoms of stridor or dysphagia. The diagnosis of a vascular ring can be made on the basis of characteristic findings on barium swallow or identification of vascular anatomy via echocardiography [7]. Although angiography has been used to further delineate the arch anatomy, recently gadolinium-enhanced magnetic resonance angiography (MRA), or computerized axial tomography (CT), has avoided the need for invasive testing [8].

The most common vascular rings include double aortic arch and right aortic arch with an aberrant left subclavian artery [2, 5, 6]. When the dorsal aortic portion of a double arch is atretic, visualization is problematic for imaging modalities depending on the presence of flow (e.g., color Doppler or MRA). In such patients, the atretic left dorsal aortic segment is usually not visualized and the anatomy mimics right aortic arch with mirror image branching (Fig. 1). A right aortic arch with mirror image branching is usually not a true vascular ring and is a finding often associated with additional intracardiac lesions; therefore, the distinction of a right aortic arch from an double aortic arch with atretic left dorsal aorta is clinically important in the symptomatic patient. We hypothesize that an accurate diagnosis is made by noting left subclavian artery distortion, which is the result of traction by the atretic left dorsal aorta.

Fig. 1
figure 1

Drawing contrasting left subclavian artery course in double aortic arch (with atretic left arch) versus right aortic arch (with mirror image branching). (A) In double aortic arch with atretic left arch, the vessel branching mimics right aortic arch with mirror image branching. However, the left subclavian artery is tethered inferiorly (asterisk) by the atretic left arch, which connects the left subclavian artery to the descending aorta. (B) In contrast, the left subclavian artery is not distorted in right aortic arch with mirror image branching. LSC, left subclavian artery; LCC, left common carotid artery; RCC, right common cardotid artery; RSC, right subclavian artery.

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Materials and Methods

Patients

Patients identified from the Johns Hopkins Hospital Pediatric Echocardiography Laboratory database were reviewed in this retrospective case series. We selected patients with the diagnosis of vascular ring from September 1995 to January 2004. Thirty patients were identified, 26 of whom underwent magnetic resonance imaging (MRI) for additional definition of the vascular anatomy (Table 1). Seven of the 26 patients were found to have either a double aortic arch or double aortic arch with atretic left dorsal aortat surgery. MRI and MRA were available for review in 6 of these 7 cases. Ages ranged from 3 days to 9 months, and 2 patients were female and 4 male. Ten patients were identified with right aortic arch and mirror image branching; images of 6 patients were available for comparison. None of these patients had symptoms of stridor or dysphagia. Of these 6 patients, 5 were male and 1 was female. Ages ranged from 1 1/2 to 17 years. Five patients had tetralogy of Fallot, and 1 patient had right pulmonary artery stenosis.

Table 1 MRI diagnosis of patients referred for evaluation of a vascular ring
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The Johns Hopkins Medicine Institutional Review Board approved this protocol.

Magnetic Resonance Imaging/Angiography Protocol and Imaging Analysis

MRI was performed on a 1.5-T scanner (CV/i, General Electric Health Systems, Waukesha, WI, USA). After localizing images, axial double-inversion recovery fast spin echo images were obtained from the thoracic inlet to the diaphragm (TR, 1–2 RR intervals; TE, 5; 20- to 36-cm field of view adjusted for patient size; matrix, 256 × 192–256; slice thickness, 6–8 mm). Sagittal oblique double-inversion recovery fast spin echo images were obtained through the aortic arch using the same parameters. Three-dimensional (3D) MRA was performed after intravenous bolus administration of 0.2 mmol/kg gadodiamide (TR, 4.5–5.5; TE, 1.7; matrix, 256 × 192 interpolated to 512 × 512; 2- or 3-mm slice thickness; coronal acquisition plane). 3D MRA was reconstructed on a separate workstation (Advantage Windows 4.1, General Electric Health Systems) using maximum-intensity projection and surface rendering algorithms.

Two observers reviewed all images independently. The presence of posterior and inferior distortion of the left subclavian artery course was used to indicate left subclavian artery distortion.

Results

The course of the left subclavian artery was examined in patients with double aortic arch and compared to that present in the six patients with right aortic arch mirror image branching. In the three patients with double arch and atretic left dorsal aorta, the left subclavian artery course was distorted, resulting in an inferior convexity in the initial takeoff from the innominant artery (Figs. 2a and 2b). The left subclavian artery course was not distorted in any of the three patients in whom both arches were patent (Figs. 2c and 2d) or in any of the patients with right aortic arch mirror image branching (Figs. 2e and 2f).

Fig. 2
figure 2

Three-dimensional surface rendered images. (A, B) Double aortic arch with atretic left arch. The left subclavian artery course is distorted (asterisk) due to torsion by the ligamentum (i.e., atertic left dorsal arch), which connects the left subclavian artery with the descending aorta. This results in the left subclavian artery having an inferior convexity to its initial course. In contrast, the left subclavian artery course is not distorted in double aortic arch, where both arches are patent. (C, D) Not appreciating the left subclavian artery distortion in double aortic arch with an atretic left arch can result in confusion because the vessel branching mimics that seen in right aortic arch with mirror image branching (E, F). LSC, left subclavian artery; LCC, left common carotid artery; RCC, right common cardotid artery; RSC, right subclavian artery.

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MRI did not directly visualize the atretic left arch in any patients. Completion of the vascular ring by the atretic arch was inferred to be present based on the distorted left subclavian artery course on MRA and the presence of clinical symptoms including stridor or dysphagia. In addition, in two of three patients, a diverticulum arising from the descending aorta represented the patent portion of the atretic left dorsal aorta (Figs. 2a and 2b). Axial double-inversion recovery images also demonstrated the more posterior subclavian artery origin in patients with double aortic arch and atretic left dorsal aorta (Fig. 3). The atretic left dorsal aorta connecting with the descending aorta tethered the left subclavian artery position posteriorly. Of the three patients with double aortic arch with atretic left dorsal aorta, only one had documented evidence of tracheal compression by MRI axial imaging.

Fig. 3
figure 3

Axial fast spin echo images demonstrating the position of the left subclavian artery. In both double aortic arch with patent (A) and atretic (B) left arch, the left subclavian artery position is posterior relative to the position of the trachea. With right aortic arch and mirror image branching (C), the left subclavian artery is more anterior. LSC, left subclavian artery; LCC, left common carotid artery; RCC, right common cardotid artery; RSC, right subclavian artery.

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Surgical observation confirmed the MRI findings in all patients referred for intervention (Fig. 4). All patients with double aortic arch on MRI had surgery.

Fig. 4
figure 4

Intraoperative appearance of double aortic arch with atretic left arch. (A) Preoperative appearance via left thoracotomy. The tie encircles the dorsal atretic component of the left arch, and its connection inferiorly with the descending aorta (arrow) is noted. The recurrent larnygeal nerve (R) crosses the atretic left arch. (B) Postoperative appearance after the atretic arch is divided. Note the ties on the two divided segments. By dividing the distal atretic arch, the left subclavian artery vascular ring is released, thereby freeing the esophagus (E). A = Anterior, P = Posterior, C = Cranial

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Discussion

Barium swallow, echocardiography, angiography, CT, and MRI all diagnose vascular rings. Barium swallow is an excellent means for screening, although other imaging modalities better delineate the vascular anatomy [1, 3]. Arteriography is now rarely performed due to the availability of noninvasive techniques. Echocardiography achieves a reliable diagnosis in most patient, but adequacy of images is operator dependent [7]. Although both MRI and CT consistently provide reliable images, both have minor associated risks. The later exposes the patient to ionizing radiation, and the former often necessitates general anesthesia and airway intubation in patients with probable airway compression.

The many variations of vascular ring anatomy can confuse the less experienced diagnostician. The most common true rings are double aortic arch and right aortic arch with aberrant left subclavian artery. We describe a group of symptomatic patients with a less common and less well-recognized variation—double aortic arch with atretic left dorsal aorta. The vascular ring in these patients was completed by the atretic left dorsal aorta and the imaging appearance mimicked the much more common (and generally asymptomatic) diagnosis of right aortic arch with mirror image branching. Because all patients in our vascular ring group were less than 1 year of age, particular attention is necessary in the interpretation of imaging studies of these symptomatic children.

The incidence of right aortic arch in autopsy and radiographic studies is estimated to be 1 in 1000–1700 individuals [2, 6]. Nearly all patients with right aortic arch and mirror image branching have associated intracardiac anomalies, and rarely do they present with vascular rings [5, 6]. Patients with right aortic arches most often come to clinical attention secondary to cyanosis or a murmur rather than the typical symptoms of stridor and dysphagia seen in patients with vascular rings. Vascular rings in patients with right aortic arch and mirror image branching have rarely been reported; the ring is completed by a left ductus from the descending aorta to the pulmonary artery [4, 9].

Our study identified the course of the left subclavian artery by MRI as a helpful aid in imaging patients with suspected vascular rings. The diverticulum demonstrated in two of our patients is an additional clue to an imperforate vessel or ligamentum connecting the decending aorta to the subclavian artery. Although this study does not have the power to evaluate the sensitivity or specificity of these findings, the diagnostician should consider the diagnosis of double aortic arch with an atretic left dorsal aorta in the symptomatic patient.

In patients with suspected vascular rings, inferior and posterior distortion of the left subclavian artery course, with or without a diverticulum, suggests the presence of a complete ring. Particularly in the symptomatic patient, this important observation aids the clinician in avoiding the misdiagnosis of right aortic arch with mirror image branching, which may result in delayed diagnosis of a vascular ring or unnecessary additional imaging.