Cases of high lying azygos arch and its embryological consideration
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ANATOMIC VARIATIONS
Cases of high lying azygos arch and its embryological consideration Min Young Yoo1 · Sung Jin Kim2,3 · Jin Young Yoo3 Received: 24 March 2020 / Accepted: 11 September 2020 © Springer-Verlag France SAS, part of Springer Nature 2020
Abstract Purpose This study aimed to report cases of high-lying azygos arch and discuss the embryological basis of its development by a thorough evaluation of the anatomical features assessed using computed tomography (CT) images. Methods This study was approved by our institutional review board. We retrospectively reviewed chest CT images between November 2011 and November 2018. To determine high-lying azygos arch, we set the upper margin of the T4 vertebral body as the reference level. Regarding the embryological development of high-lying azygos arch, we retrospectively reviewed the CT images of 105 patients with tracheal bronchus to identify the location of the azygos arch. Results We noted that on three cases CT images, the azygos arch was located higher than the upper margin of the right main bronchus, and drained into the proximal superior vena cava (SVC) at a level higher than the conventional T4 or T5 vertebral level. All 105 patients with right tracheal bronchus showed azygos arch above the tracheal bronchus. Conclusion This variation in the location of the azygos arch can mimic pathological lesion on plain radiographs, and, therefore, it is important to be aware of high-lying azygos arch. Our findings show that the azygos arch may have possibly migrated downward during embryological development. Keywords Azygos arch · Embryo · Lymphadenopathy · Computed tomography · Azygos vein · Anatomical variation
Introduction The azygos vein typically starts from the posterior aspect of the inferior vena cava, at or below the level of the renal veins, although its origin is variable. The lumbar azygos is known to ascend anterior to the upper lumbar vertebrae [4, 7–9]. It may pass behind the right crus of the diaphragm or pass through it or may traverse the aortic hiatus to the right of the cisterna chyli. Anterior to the 12th thoracic vertebral body, the azygos is joined by a large vessel formed by the right ascending lumbar and subcostal veins that passes forward and to the right of the 12th thoracic vertebra behind the right crus; in the absence of a lumbar azygos, this common * Jin Young Yoo [email protected] 1
Department of Nuclear Medicine, Chungbuk National University Hospital, Cheongju, Korea
2
Department of Radiology, Chungbuk National University College of Medicine, Cheongju, Korea
3
Department of Radiology, Chungbuk National University Hospital, 776, 1 Sunhwan‑ro, Seowon‑gu, Cheongju‑si 362‑711, Chungcheongbuk‑do, Korea
trunk itself may form the azygos vein. Irrespective of its origin, the azygos vein ascends in the posterior mediastinum to the level of the fourth or fifth thoracic vertebra [8], where it arches forward above the right pulmonary hilum [7]. The azygos arch, where the azygos vein terminates, is known to be located at the leve
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