european urology supplements 5 (2006) 444 448 available at www.sciencedirect.com journal homepage: www.europeanurology.com Circumcaval Ureter: Embryology Arianna Lesma *, Aldo Bocciardi, Patrizio Rigatti Department of Urology, Università Vita-Salute San Raffaele, Milan, Italy Article info Keywords: Anomalies Circumcaval Embryology Retrocaval Ureter Abstract Objectives: A circumcaval ureter is a rare congenital anomaly usually associated with upper urinary tract stasis and an S or fishhook deformity of the ureter, in which the ureter itself passes behind the inferior vena cava. Aim of this paper was to debate novel issues concerning the embryologic anomaly of the inferior vena cava which may lead to the ureter obstruction and hydronephrosis. Methods: Search of published literature and meeting abstracts. Results: A circumcaval ureter results from the posterior cardinal vein persisting as the renal segment of the inferior vena cava during development. Normally, the inferior vena cava develops from the vitelline vein, subcardinal and sacrocardinal veins, which must undergo sequential development, anastomosis and regression to become the inferior vena cava. Normally, the right vitelline vein forms the pre-renal or hepatic segment of the inferior vena cava, the right subcardinal vein forms the renal segment and the right sacrocardinal vein forms the postrenal vena cava. Typically, the circumcaval ureter aetiology is assumed to be abnormal embryologic development of the vena cava as a result of atrophy failure of the right posterior cardinal vein in the lumbar portion. Whether the renal segment of inferior vena cava is formed from the right posterior cardinal vein that lies ventral to the ureter, then the ureter will develop in a circumcaval position. Conclusions: Although this embryologic anomaly is commonly known to urologists as circumcaval or retrocaval ureter terms that are anatomically descriptive but misleading in regards to development it is not the result of an abnormality in ureteral development but rather an anomaly in the development of the inferior vena cava. The term preureteral vena cava may thus emphasize that the circumcaval ureter results from altered vascular, rather than ureteral development. # 2006 Elsevier B.V. All rights reserved. * Corresponding author. U.O. di Urologia, Istituto Scientifico Universitario Ospedale San Raffaele, Via Olgettina 60, 20132 Milan, Italy. Tel. +39 02 26437286; Fax: +39 02 26437298. E-mail address: lesma.arianna@hsr.it (A. Lesma). 1569-9056/$ see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.eursup.2006.02.008
european urology supplements 5 (2006) 444 448 445 Fig. 1 Main components of the foetal venous and arterial systems at the end of the 4th week. 1. Embryology Fig. 3 Venous system in human embryo at the sixth week. Fig. 2 Venous system in human embryo at the fifth week. The circumcaval ureter is caused by an abnormal embryological development of the inferior vena cava (IVC) [1 6]. Thus, a brief description of the embryo vascular system, with special regard to the venous system, is presented. In the fourth week, three pairs of major veins can be distinguished: the vitelline veins or omphalomesenteric veins, which carry blood from the yolk sac to the sinus venosus; the umbilical veins, which originate in the chorionic villi and carry oxygenated blood to the embryo; and the cardinal veins, which drain the body of the embryo proper. Throughout the fourth week the cardinal veins form the main venous drainage system of the embryo. This system consists of the anterior or
446 european urology supplements 5 (2006) 444 448 superior cardinal veins, which drain the cephalic part of the embryo and the posterior or inferior cardinal veins, which drain the rest of the embryo. The anterior and posterior veins join to form the short common cardinal veins and enter the sinus horn (Fig. 1). During the fifth week the subcardinal or postcardinal veins, which drain the mesonephrons, are formed. They develop ventromedially to the mesonephron and run parallel to the posterior cardinal veins. The posterior cardinal veins and subcardinal veins lie ventrally to the developing ureter, but posterior cardinal veins run laterally to the developing ureter, whereas subcardinal veins run medially. Subcardinal veins connect with the posterior cardinal veins through multiple anastomosis. The sacrocardinal veins, which drain the lower extremities, are also formed during this week (Fig. 2). During the sixth week the supracardinal veins, which drain the body wall by way of the intercostals Fig. 5 Development of the renal segment of the inferior vena cava. Fig. 4 Development of the superior vena cava. veins and take over the functions of the posterior cardinal veins, are formed. The supracardinal veins lie medially to the posterior cardinal veins, laterally to the subcardinal veins, and dorsally to the developing ureter (Fig. 3). Formation of the vena cava system is characterised by the appearance of anastomoses between left and right such that the blood from the left is channelled to the right side. The anastomosis between the anterior cardinal veins develops into the left brachiocephalic vein. Most of the blood from the left side of the head and the left upper extremity is then channelled to the right. The proximal portion of the left posterior cardinal vein that enters into the left brachiocephalic vein is retained as the left superior intercostal vein. This vessel receives blood from the second and third intercostal spaces. The superior vena cava is formed by the right common cardinal vein and the proximal portion of the right anterior cardinal vein (Fig. 4). The IVC starts to form during the sixth week. Several events occur between the sixth and eighth weeks of gestation, when the formation of the IVC is complete. The anastomosis between the subcardinal veins forms the left renal vein. When this communication has been established, the left subcardinal vein disappears, and only its distal portion remains as
european urology supplements 5 (2006) 444 448 447 the left gonadal vein. Hence the right subcardinal vein becomes the main drainage channel and develops into the renal segment of the IVC (Fig. 5). The anastomosis between the sacrocardinal veins forms the left common iliac vein. The right sacrocardinal vein becomes the sacrocardinal segment of the IVC. The right vitelline vein forms the hepatic segment of the IVC. When the renal segment of the IVC connects with the hepatic segment, the IVC, which consists of hepatic, renal, and sacrocardinal segments, is complete (Fig. 6). Supracardinal veins do not contribute to the development of the vena cava, but to the azygos and hemiazygos vein systems. Hence, with obliteration of the major portion of the posterior cardinal veins, the supracardinal veins assume a greater role in draining the body wall. The fourth to 11th right Fig. 7 Circumcaval ureter. Fig. 6 The venous system at birth showing the three components of the IVC: hepatic (grey), renal (blue), and sacrocardinal (red) segments. intercostal veins empty into the right supracardinal vein, which together with a portion of the posterior cardinal veins forms the azygos vein. On the left the fourth to seventh intercostal veins enter into the left supracardinal vein. The left supracardinal vein, then known as the hemiazygos vein, empties into the azygos vein. Should the right posterior cardinal vein, which is lateral to the definitive ureteral position, rather than the right subcardinal vein persist as the renal segment of the IVC, a circumcaval ureter would result (Fig. 7). Interestingly, when the definitive vena cava forms normally and the ventral portion of the primitive rings also persists, a double right vena cava is formed because of the persistence of both the right subcardinal vein dorsally and the right subcardinal vein ventrally. The resulting double vein
448 european urology supplements 5 (2006) 444 448 cava may trap the right ureter between its limb [7,8]. Whether a bilateral vena cava is associated with a circumcaval ureter, the anomalous ureter has been reported only on the right side, which supports the thesis that the right vena cava develops abnormally from a persistent subcardinal vein, whereas the left vena cava develops from the left supracardinal vein but otherwise normally [9]. References [1] Bateson E, Atkinson D. Circumcaval ureter: a new classification. Clin Radiol 1969;20:173 7. [2] Bissi A, Rigatti P. L uretere circumcavale. Chir Arch Trim 1977; 41 (Suppl). [3] Hamilton WJ, Boyd JD, Mossman HW. Human embryology. Cambridge: W. Heffer & Sons Limited; 1959 p. 162 68. [4] Belman AB, King LR, Kramer SA, editors. Clinical pediatric urology, ed. 9 London: Martin Dunitz; 2002. [5] Sadler TW. Langman s medical embryology, ed. 4 Philadelphia: Lippincott Williams & Wilkins; 2004. [6] Bass FE, Redwine MD, Kramer LA, Huynh PT, Harris JH. Spectrum of congenital anomalies of the inferior vena cava: cross-sectional imaging findings. RadioGraphics 2000;20:639 52. [7] Gruenwald P, Surks SN. Pre-ureteric vena cava and its embryological explanation. J Urol 1943;49:195. [8] Sasai K, Sano A, Imanaka K, et al. Right periureteric venous ring detected by computed tomography. J Comput Assist Tomogr 1986;10:349 51. [9] Pick JW, Anson BJ. Retrocaval ureter: report of a case with discussion of its clinical significance. J Urol 1940;43:672.