Tuesday, August 12, 2008
The ureters are bilateral tubular structures responsible for transporting urine from the renal pelvis to the bladder (see Fig. 1-1 ). They are generally 22 to 30 cm in length with a wall composed of multiple layers ( Fig. 1-43 ). The inner layer is transitional epithelium. Next is the lamina propria. This is a connective tissue layer that along with the epithelium makes up the mucosal lining. Overlying the lamina propria is a layer of smooth muscle that is contiguous with muscle covering the renal calyces and pelvis, although in the ureter this layer is divided into an inner longitudinal and an outer circular layer. Together, these muscular layers provide the peristaltic wave that actively transports urine from the renal collecting system through the ureter to the bladder. The outermost layer is the adventitia. This thin layer surrounds the ureter and encompasses the blood vessels and lymphatics that travel along the ureter.
Key to many urologic procedures is an understanding of ureteral anatomic relationships. The ureter begins at the ureteropelvic junction, which lies posterior to the renal artery and vein. It then progresses inferiorly along the anterior edge of the psoas muscle. Anteriorly, the right ureter is related to the ascending colon, cecum, colonic mesentery, and appendix. The left ureter is closely related to the descending and sigmoid colon and their accompanying mesenteries. Approximately a third of the way to the bladder the ureter is crossed anteriorly by the gonadal vessels. As it enters the pelvis the ureter crosses anterior to the iliac vessels. This crossover point is usually at the bifurcation of the common iliac into the internal and external iliac arteries, thus making this a useful landmark for pelvic procedures.
Given the proximity of the ureters to several bowel segments, malignant and inflammatory processes of the terminal ileum, appendix, right or left colon, and sigmoid colon may involve the ureter. Effects can range from microhematuria to fistula or total obstruction. Within the female pelvis, the ureters are crossed anteriorly by the uterine arteries and are closely related to the uterine cervix. This location places the ureters at risk during hysterectomy. Pathologic processes of the fallopian tube and ovary may also encroach on the ureter at the pelvic brim.Normal Variations in Ureteral Caliber
The normal ureter is not of uniform caliber, with three distinct narrowings classically described: the ureteropelvic junction, crossing of the iliac vessels, and the ureterovesical junction ( Fig. 1-44 ). At the ureteropelvic junction, the renal pelvis tapers into the proximal ureter. In many cases, this perceived narrowing may be more apparent than real, with no evidence of obstruction evident on radiographic or endoscopic investigation. The second region of narrowing occurs as the ureter crosses the iliac vessels. This is due to a combination of extrinsic compression of the ureter by the iliac vessels and the necessary anterior angulation of the ureter as it crosses the iliac vessels to enter into the pelvis. There is also no intrinsic change in the ureteral caliber at this location. The third site of narrowing observed in the normal ureter is the ureterovesical junction. There is a true physical restriction of the ureter as it makes the intramural passage through the bladder wall to the ureteral orifice. These three sites of ureteral narrowing are clinically significant because they are common locations for urinary calculi to lodge during passage. In addition, the angulation of the ureter, first anteriorly as it passes over the iliac vessels, then posteromedially as it enters the pelvis and courses behind the bladder, may restrict successful passage of rigid endoscopes. Appreciation of this normal angulation and the three-dimensional course of the ureter is critical for safe and successful ureteral endoscopy.
Ureteral Segmentation and Nomenclature
The ureter is often arbitrarily divided into segments to facilitate ureteral description. The simplest system divides the ureter into the abdominal ureter extending from renal pelvis to the iliac vessels and the pelvic ureter extending from the iliac vessels to the bladder. Alternatively, the ureter can be divided into upper, middle, and lower segments ( Fig. 1-45 ). The upper ureter extends from the renal pelvis to the upper border of the sacrum. The middle ureter comprises the segment from the upper to the lower border of the sacrum. The lower (distal or pelvic) ureter extends from the lower border of the sacrum to the bladder.
Ureteral Blood Supply and Lymphatic Drainage
The ureter receives its blood supply from multiple arterial branches along its course ( Fig. 1-46 ). Of greatest importance to the surgeon is that arterial branches to the abdominal ureter approach from a medial direction whereas arterial branches to the pelvic ureter approach from a lateral direction. For the upper ureter these branches originate from the renal artery, gonadal artery, abdominal aorta, and common iliac artery. After entering the pelvis, additional small arterial branches to the distal ureter may arise from the internal iliac artery or its branches, especially the vesical and uterine arteries, but also from the middle rectal and vaginal arteries. After reaching the ureter, the arterial vessels course longitudinally within the periureteral adventitia in an extensive anastomosing plexus. It is this longitudinal vascularity that allows the ureter to be safely mobilized from the surrounding retroperitoneal tissues without compromising the vascular supply, provided that the periureteral adventitia is not stripped. The venous and lymphatic drainage of the ureter parallels the arterial supply. Thus, ureteral lymphatic drainage varies by ureteral level. In the pelvis, ureteral lymphatics drain to internal, external, and common iliac nodes. In the abdomen, the left para-aortic lymph nodes are the primary drainage site for the left ureter whereas the abdominal portion of the right ureter is drained primarily to right paracaval and interaortocaval lymph nodes. The lymphatic drainage of the upper ureter and renal pelvis tends to join the renal lymphatics and is identical to that of the ipsilateral kidney.
The exact role of the ureteral autonomic input is unclear. Normal ureteral peristalsis does not require outside autonomic input but, rather, originates and is propagated from intrinsic smooth muscle pacemaker sites located in the minor calyces of the renal collecting system. The autonomic nervous system may exert some modulating effect on this process, but the exact role is unclear. The ureter receives preganglionic sympathetic input from the 10th thoracic through 2nd lumbar spinal segments. Postganglionic fibers arise from several ganglia in the aorticorenal, superior, and inferior hypogastric autonomic plexuses. Parasympathetic input is received from the 2nd through 4th sacral spinal segments.Pain Perception and Somatic Referral
Renal pain fibers are stimulated by tension (distention) in the renal capsule, renal collecting system, or ureter. Direct mucosal irritation in the upper urinary tract may also stimulate nociceptors. Signals travel with the sympathetic nerves and result in a visceral-type pain referred to the sympathetic distribution of the kidney and ureter (eighth thoracic through second lumbar). Pain and reflex muscle spasm are typically produced over the distributions of the subcostal, iliohypogastric, ilioinguinal, and/or genitofemoral nerves, resulting in flank, groin, or scrotal (or labial) pain and hyperalgesia, depending on the location of the noxious visceral stimulus ( Fig. 1-47 ).