The normal right ureter runs lateral to the inferior vena cava (IVC). A retrocaval (also known as circumcaval) ureter is a congenital anomaly in which the right ureter passes posterior to the IVC, emerges between the IVC and aorta, and then recrosses the iliac vessels anteriorly before inserting into the bladder. The portion of the ureter lying posterior to the IVC becomes obstructed, leading to dilation of the more proximal parts of the urine collecting system. This obstruction can become symptomatic during childhood or, more commonly, adulthood. The exact incidence of retrocaval ureter is uncertain but is likely 1 : 1000 to 1 : 1500, with males affected more often than females.
A retrocaval ureter reﬂects abnormal development not of the ureter, but rather of the IVC. In the fourth week of gestation, the cardinal system of veins drains the body of the developing embryo. This system is divided into the two major branches: the anterior cardinal veins, which drain the superior portion of the embryo; and the posterior cardinal veins, which drain the inferior portion of the embryo. These join to form a common cardinal vein, which drains into the sinus venosus. Meanwhile, the vitelline veins, the precursors of the portal system, drain blood from the yolk sac to the sinus venosus. Finally, the umbilical veins carry oxygenated blood from the placenta to the embryo.
In the ﬁfth week, the subcardinal veins develop parallel to the posterior cardinal veins. Both the subcardinal and posterior cardinal veins lie anterior to the developing ureters; however, as renal ascent progresses, the subcardinal veins become positioned medial to the ureters, whereas the posterior cardinal veins become lateral. During the ﬁfth week, the sacrocardinal veins also appear at the caudal end of the posterior cardinal veins and lie posterior to the developing ureters.
In the sixth week, the supracardinal veins form parallel to the posterior cardinal veins and largely take over their function of draining the posterior body wall. These lie medial to the posterior cardinal veins and dorsolateral to the developing ureters. As the supracardinal veins develop, the posterior cardinal veins degenerate. At this point, numerous anastomoses have formed between corresponding left- and right-sided structures.
During the sixth to eighth weeks of development, the IVC forms through the selective fusion and degeneration of these embryonic vessels. The sacrocardinal veins give rise to the common iliac veins and the distal end of the IVC. The right subcardinal vein gives rise to the renal segment of the IVC, as well as to the renal and gonadal veins. The right vitelline vein gives rise to the hepatic segment of the IVC. The supracardinal veins give rise to the azygous and hemiazygos veins. (According to some sources, the right supracardinal vein also contributes to the infrarenal segment of the IVC.)
As a result of this process, the entire IVC normally lies medial to the ureter. If, however, the right posterior cardinal vein persists to form the renal segment of the IVC, then the ureter will lie medial and posterior to the IVC in the renal segment, causing it to take a retrocaval course.
Presentation And Diagnosis
As expected, individuals with a retrocaval ureter have symptoms of ureteral obstruction, which include abdominal or right ﬂank pain, chronic nausea, recurrent urinary infection due to urinary stasis, and hematuria following mild trauma. In many cases, however, symptoms either do not occur, or perhaps are not recognizable, until adulthood. The intermittent nature of renal colic often confuses the diagnosis. Moreover, the association with nausea often suggests gastrointestinal origin and delays diagnosis. Contextual clues of the pain facilitate the diagnosis. For example, pain may be more pronounced after ingestion of caffeinated or alcoholic beverages, which lead to brisk diuresis. Most often, the need for intervention becomes apparent when there is persistent right ﬂank pain, stone formation, recurrent urinary tract infection, pyelonephritis, or deterioration of renal function.
If the clinical suspicion of retrocaval ureter is high, the diagnosis is conﬁrmed using radiographic imaging. In the past, the standard evaluation began with intravenous pyelography, which reveals a variable degree of right-sided hydronephrosis, a medially deviated proximal ureter, a ﬁsh-hook or sickle-shaped appearance of the ureter just proximal to the IVC, and incomplete opaciﬁcation of the ureter distal to the IVC. In the modern setting, contrast-enhanced CT is preferred. The size and contour of the entire ureter can be visualized in three dimensions with reconstruction of the axial images taken at the delayed urographic phase. Although a retrograde pyelogram can also be performed to visualize a retrocaval ureter, it is more invasive and also less detailed than CT.
If intervention is needed, the ureter can be reconstructed by performing an open or laparoscopic ureteroureterostomy. Regardless of the modality, the basic steps of the procedure are the same. The renal pelvis and proximal ureter are dissected to the point where the ureter passes behind the IVC. The ureter is then divided adjacent to the lateral IVC wall, and the distal end of the ureter is removed from behind the IVC. (Some surgeons divide the ureter both lateral and medial to the IVC, effectively excluding the segment located behind the IVC.) The ureteral ends are repositioned such that the ureter takes a course lateral to the IVC. The proximal end of the ureter is typically long enough to make a tension-free, spatulated, end-to-end anastomosis without difﬁculty, which restores continuity to the ureter. A ureteral stent is deployed and left in position for several weeks after the rocedure to ensure proper healing of the anastomosis.