RETROCAVAL URETER
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.
Embryology
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.
Treatment
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.
