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The British Journal of Radiology, 82 (2009), 73–78 PICTORIAL REVIEW Non-invasive imaging of aberrant right subclavian artery pathologies and aberrant right vertebral artery 1 M KARCAALTINCABA, M ARIYUREK, MD MD, 1 M HALILOGLU, MD, 1 E OZKAN, MD, 2 M KOCAK, MD, 1 D AKINCI, MD and 1 1 Department of Radiology, Hacettepe University School of Medicine, Ankara, Turkey and 2Department of Radiology, Medical College of Wisconsin, Milwaukee, WI, USA ABSTRACT. Here, we review the CT and MR angiography findings of aberrant right subclavian and right vertebral arteries, with emphasis on the differences between these structures. In addition, non-invasive imaging findings of aberrant right subclavian artery pathologies, including arteritis, aneurysm and dissection, are discussed. Received: 13 April 2006 Revised: 8 October 2006 Accepted: 15 November 2006 DOI: 10.1259/bjr/44929969 ’ 2009 The British Institute of Radiology Recent developments in non-invasive CT and MR angiographic imaging allow the diagnosis of aortic arch anomalies and the visualization of pathological findings of anomalous arteries. Imaging features of these anomalies and the spectrum of their pathologies should be known so that a confident diagnosis can be given. The combination of three-dimensional and axial images may provide better understanding of the vascular anatomy compared with conventional angiography. Aberrant right subclavian artery (ARSA) is the most common aortic arch anomaly, with an incidence of 1–2% [1, 2]. Although aneurysm and dissection of the ARSA has been described in the literature, arteritis of this anomaly is first described here [1–5]. Aberrant right vertebral artery is an extremely rare anomaly and may mimic an ARSA by its retro-oesophageal course [6]. Non-invasive angiography using multidetector CT and MRI has now become a routine application [7, 8]. The advantages of multidetector CT angiography are ease of application, wider use of the technique and simultaneous visualization of adjacent anatomic structures. MR angiography provides high-quality multiphasic imaging without the risk of increased radiation dose, which is a significant problem with CT angiography. The aim of this pictorial review is to demonstrate non-invasive MR and CT angiographic findings from patients with normal and pathological aberrant right subclavian arteries (aneurysm and arteritis) and an aberrant right vertebral artery. Embryology and anatomy ARSA develops as a result of interruption between the right common carotid artery and the ARSA in the Address correspondence to: Musturay Karcaaltincaba, Department of Radiology, Hacettepe University School of Medicine, Ankara, Turkey. E-mail: [email protected] The British Journal of Radiology, January 2009 developing double aortic arch [9]. In the ARSA, the right fourth aortic arch and the proximal right dorsal aorta involute and the right seventh intersegmental artery develops from a persistent dorsal aorta (Figure 1). An aortic (Kommerell̀s) diverticulum may be present at the origin of this vessel, representing the remnant of the distal right aortic arch [1]. The ARSA is located posterior to the oesophagus on axial CT images, and can be seen as the last branch from the posterior margin of the aortic arch on three-dimensional images (Figure 2). The ARSA can indent the oesophagus and the trachea posteriorly, resulting in dysphagia lusoria and airway narrowing, respectively. Maethods and materials We reviewed retrospectively our archive for ARSA and its associated pathologies diagnosed between 2001 and 2003, and identified aneurysm and arteritis of ARSA and dissection of the right vertebral artery originating from ARSA. Three-dimensional non-invasive angiographic images were obtained by MR angiography and multidetector (4- and 8-channel) CT angiography. Volumerendered, maximum intensity projection (MIP) and multiplanar reformatted (MPR) images were obtained after the reconstruction of the axial slices. The aberrant right vertebral artery was incidentally diagnosed. Aneurysm Aneurysmal dilatation of the proximal segment of an ARSA is not infrequent, occurring in 8% of cases. Such an aneurysm can be associated with the Kommerell̀s diverticulum and is thought to develop secondary to atherosclerosis. Almost half of the cases with an ARSA 73 M Karcaaltincaba, M Haliloglu, E Ozkan et al Figure 1. A diagram showing the normal embryological development of the aortic arch and the development of an aberrant right subclavian artery (ARSA). (a) Normal embryological anatomy of aortic arches are displayed. (b) During normal development, most of the aortic arches involute and the 4th arch forms the aortic arch. Also, the right dorsal aorta involutes. (c) ARSA develops as a result of persistent right dorsal aorta (known as Kommerell’s diveritculum) and involution of the right 4th embryologic arch. Emrbyological aortic arches are represented in purple and involuted ones in grey. Arches in red represent persistent embryological structures in adult life (b,c). aneurysm ruptured with conservative management, prompting some authors to recommend surgery even in asymptomatic cases [1, 3]. In our case, we diagnosed an ARSA aneurysm in a patient with a truncus arteriosus anomaly (Figure 3). Interestingly, the left pulmonary artery was rising from the aortic arch and was compressed between the ARSA aneurysm and the aortic arch in this patient. Although an ARSA aneurysm can compress the trachea, left pulmonary artery compression by such an aneurysm has not been described before. Arteritis Atherosclerosis can involve the ARSA, resulting in stenosis; however, stenosis owing to arteritis of an ARSA has not been described previously. Arteritis of the ARSA developed secondary to Takayasu arteritis in our patient (Figure 4). CT angiography allowed the diagnosis in this case. Diagnosis of ARSA arteritis is important because failure to recognize this anomaly may result in a change in the surgical treatment approach or the failure of Figure 2. A 35-year-old man with an incidentally diagnosed aberrant right subclavian artery (ARSA). (a) On CT angiography (left anterior oblique projection), the ARSA is seen as the last branch from the aortic arch (arrow). (b) CT angiography (posterior projection) shows the ARSA as the only posterior branch (arrow). (c) An axial image shows the ARSA posterolateral to the oesophagus (arrow). 74 The British Journal of Radiology, January 2009 Pictorial review: Non-invasive imaging of aberrant right subclavian and right vertebral artery pathologies Figure 3. A 2-year-old girl with an aberrant right subclavian artery (ARSA) aneurysm and truncus arteriosus anomaly. (a,b) CT angiography (left posterior and superior projections) images show a dilated ARSA and fusiform aneurysm (long arrow). Note the left pulmonary artery (short arrow) arising from the aortic arch (double arrow). (c) Coronal multiplanar reformatted image shows narrowing of the left pulmonary artery (arrow) between the ARSA aneurysm (asterisk) and the aortic arch (AA). (d) An axial CT image showing the ARSA (asterisk) traversing posterior to the aortic arch and indenting the posterior wall of the trachea (T). treatment by stenosis using vascular interventional techniques [10]. Dissection Dissection of an ARSA is very rare, and only 16 cases have been reported in the literature [3]. Non-invasive imaging plays a major role in the diagnosis of dissection. Established criteria for the classification of dissection are not valid in cases with ARSA, because it arises distal to the left subclavian artery. Failure to recognize this anomaly and The British Journal of Radiology, January 2009 cross-clamping of the aorta proximal to the origin of the left subclavian artery during surgery can result in brainstem infarct secondary to occlusion of the blood supply to both vertebral arteries [5]. We observed the dissection of the right vertebral artery originating from an ARSA (Figure 5). We thought that dissection in this patient might have developed because of hypermobility of the ARSA and a susceptibility to rotational forces resulting from the increased length of the artery. Mulligan et al [5] suggested that an ARSA may show increased susceptibility to atherosclerosis and its associated complications, including aneurysms, dissections and stenosis in accordance with our observation. 75 M Karcaaltincaba, M Haliloglu, E Ozkan et al Figure 4. A 40-year-old woman with Takayasu arteritis and aberrant right subclavian artery (ARSA) involvement, resulting in right-sided subclavian steal. (a,b) CT angiography (superior left anterior oblique and left posterior oblique projections) shows severe stenosis of the ARSA (arrow). Note that vasculitis involves the retro-oesophageal segment, sparing the distal ARSA and Kommerell̀s diverticulum. (c) Axial CT image shows the normal calibre of the Kommerell̀s diverticulum (arrow). (d) Coronal thin maximum intensity projection image demonstrates wall thickening and narrowing of the ARSA, consistent with vasculitis. These findings were not visible on conventional angiography. Aberrant right vertebral artery An aberrant right vertebral artery arises from the dorsal margin of the aortic arch as the last branch, similar to an ARSA [6]. The proximal segment of the aberrant right vertebral artery is located posterior to the oesophagus and, cranially, the artery ascends to the vertebral foramen, in contradistinction to an ARSA that travels towards the right shoulder (Figure 6). Diagnosis of aberrant right vertebral artery is important especially in patients with dissection who will undergo surgical treatment, because failure to do so may result in bilateral brain stem infarction after crossclamping of the aorta proximal to the left subclavian 76 artery. The aberrant right vertebral artery may mimic an ARSA, especially when it is stenotic, by its retrooesophageal course. However, a normal right subclavian artery exists in the presence of an aberrant right vertebral artery, and has a small calibre compared with the ARSA. Conclusions Familiarity with the non-invasive imaging findings of ARSA pathologies and aberrant right vertebral artery is crucial for correct diagnosis. It should be kept in mind that other pathological conditions may coexist with ARSA. The British Journal of Radiology, January 2009 Pictorial review: Non-invasive imaging of aberrant right subclavian and right vertebral artery pathologies Figure 5. A 42-year-old man with right vertebral artery (RVA) dissection (arrow) and aberrant right subclavian artery (ARSA). (a,b) MR angiography, coronal thin maximum intensity projection and coronal volume-rendered projections show a dissected vertebral artery arising from the ARSA. (c,d). Diffusion-weighted MR image and head CT image show infarct in the right cerebellum as a result of dissection. The British Journal of Radiology, January 2009 77 M Karcaaltincaba, M Haliloglu, E Ozkan et al Figure 6. A 59-year-old woman with an incidentally diagnosed aberrant right vertebral artery (RVA). (a) Axial CT image shows the retro-oesophageal course of the aberrant RVA. (b) Curved planar reformatted image shows the aberrant RVA traversing towards the right vertebral canal. (c,d) CT angiography (left posterior oblique projections) shows the aberrant RVA as the last branch from the posterior aspect of the aortic arch. Kommerell̀s diverticulum (arrow) is also seen at the origin of the aberrant RVA. LCCA, left common carotid artery; RCCA, right common carotid artery; LVA, left vertebral artery; LSA, left subclavian artery; RSA, right subclavian artery. Reprinted with permission from [6]. References 1. Freed K, Low V HS. The aberrant subclavian artery. 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Eur Radiol 2006;(Suppl 2):B3–8. 9. Davies M, Guest PJ. Developmental abnormalities of the great vessels of the thorax and their embryological basis. Br J Radiol 2003;76:491–502. 10. Azakie A, McElhinney DB, Dowd CF, Stoney RJ. Percutaneous stenting for symptomatic stenosis of aberrant right subclavian artery. J Vasc Surg 1998;27:756–8. The British Journal of Radiology, January 2009