Sep 13, 2020
The ureter is the long thin little muscular structure that transports urine from the kidneys to the bladder.
The ureter is a relatively small player in the urinary system but a very important one. It doesn’t get talked about enough because it is often thought of as just a transport tube from the kidneys, the star of the show where the urine is made, to the bladder, the supporting actor, where the urine is stored.
What is most striking to me as a surgeon is how delicate the ureter is to have such a critical function to getting waste products out of the body, , how small it is and occasionally hard to identify within the body, how easily it can be injured during an operation, and how delicate we have to be when we operate.
There’s a lot relying on these little guys to do their job.
The ureters are long, usually 20–30 cm (8-12 inches) long and around 3–4 mm (1/8 to ¼ inch American) in diameter. From the renal pelvis, they descend on top of the psoas major muscle to reach the brim of the pelvis. Then they cross in front of the common iliac arteries down along the sides of the pelvis, and finally curve forward and enter the bladder at the back of the bladder, tunneling through the bladder wall before opening into the bladder on its back surface at the level of the trigone of the bladder at small openings called the ureteral orifices.
The inner lumen of the ureter is lined by transitional cells, the same type of cells that lines the urinary bladder. The transitional cell urothelium stretches in the ureters, appearing as a layer of column-shaped cells when relaxed, and of flatter cells when stretched and distended.
Below the epithelium sits the lamina propria, a connective tissue layer with many elastic fibers, blood vessels, veins and lymphatic channels.
The ureter’s outer layers are two muscular layers, an inner longitudinal layer of muscle, and an outer circular or spiral layer of muscle. The lower third of the ureter has a third muscular layer.
Because of it’s length along the body the ureter’s blood supply (arteries and veins), lymphatic drainage and nerve innervation come from many different sources at the levels along it’s path.
The ureters can be affected by a number of diseases.
Kidney stones are the most common problem. The ureters are so narrow it doesn’t take a very big stone to get stuck in the middle. Stones even as small as 1-2 mm may get stuck in the ureter (although some ureters can pass stones as large as a centimeter). When the stone gets stuck the urine cannot pass. The urine backing up stretches the ureter and renal pelvis behind it causing hydronephrosis or hydroureteronephrosis. The muscular renal pelvis and ureter try to push the urine out with peristaltic waves of muscular contraction. The pressure buildup and stretch receptors in the renal pelvis and ureter cause pain. The pain often comes in waves and is referred to as renal colic. Because the nerve innervation comes from several levels along the course of the ureter the pain can be felt sometimes in the back, sometimes in the flank, or sometimes radiating around to the front lower abdomen and down into the testicle, scrotum or labia. To get a stone that is stuck in the ureter out of the body often requires a scope procedure called ureteroscopy to look into the ureter and pull out the stone and/or to break it up using a holmium laser.
The ureter can also be blocked by obstruction. Obstruction of the ureter can occur intrinsically, as a result of narrowing within the ureter, or extrinsically, compression or fibrosis of structures around the ureter pushing on the ureter to narrow it.
Intrinsic blockage can come from strictures, congenital or acquired, and ureteropelvic junction obstruction from abnormal development at that junction or from obstructive ureteroceles.
Extrinsic compression can come from cancer, endometriosis, tuberculosis and schistosomiasis, and retroperitoneal fibrosis.
A narrowed ureter leads to hydronephrosis and hydroureteronephrosis similar to a kidney stone but it does not always lead to pain because the conditions are usually more chronic. Other symptoms may be blood in the urine, infection, or a loss of kidney function. Often the condition is found incidentally, when an x-ray, ultrasound or CT scan is done for another condition.
Treatment of any of these obstructions may involve treatment of the underlying conditions as well as ureteral stenting or nephrostomy tube, ureterolysis in the case of retroperitoneal fibrosis, or reinserting the ureters into a new place on the bladder called reimplantation.
Another class of ureteral problem is congenital abnormalities that affect the ureters, which can include the development of two ureters on the same side with subsequent obstruction and/or reflux, or abnormally placed ureters, called the ectopic ureter.
Variants of ureteral anatomy such as duplication occur when the ureteric bud, an outpouching from the mesonephric duct, which forms the ureter, develops abnormally, sometimes duplicating completely or incompletely or budding from an abnormal position so the ureter drains not on the trigone of the bladder but higher or lower in the bladder, in the prostate, urethra or vagina.
Congenital abnormalities can present with a number of symptoms and may need to be treated very early in life in some cases.
Another condition commonly seen in children is vesicoureteral reflux. Reflux is when urine is pushed back into the ureter during urination. In the normal situation the ureter tunneling through the bladder creates an area of the ureter that prevents urine from going back into the ureter during urination. Many children with this vesicoureteral reflux have the reflux resolve as the bladder develops through childhood. The amount of reflux can be mild, going just to the end of the ureter, or severe, going to the renal pelvis and dilating the system from the backflow. Symptoms are most commonly recurrent infections. Occasionally surgery is needed to reimplant the ureter and correct the reflux.
Lastly, I would like to mention ureteral cancer. Ureteral cancer is most often cancer of the cells lining the ureter, the transitional cells, and is called transitional cell carcinoma This is a similar cancer to most bladder cancers. Bladder cancers are more common that ureteral or renal pelvic tumors, but the risk factors are largely the same, including smoking and exposure to dyes such as aromatic amines and aldehydes. The most common symptom is blood in the urine. Diagnosis is made radiographically and through visual inspection called ureteroscopy. Treatment most often requires removal of the entire ureter, renal pelvis, and kidney on that side. For more information on that you can listen to the last episode of this podcast, an interview I had with Dr Mikhail Regelman about a procedure called nephroureterectomy.
Find more episodes and connect with me at whyurologypodcast.com.