What is the pathogenesis of ureteral calculi?

Ureteral calculi mostly originate from primary kidney calculi, and descend to the ureter due to gravity and urinary peristalsis. Therefore, the composition of ureteral stones is the same as that of kidney calculi, mainly oxalate stones, followed by uric acid stones. Primary ureteral calculi are rare and often secondary to some ureteral diseases, such as ureteral polyps, tumors, cysts, strictures, diverticulum and ureteral hypertrophy. Because urine stays in the ureter, stones are formed in the accumulation and expansion of urine.

After the formation of ureteral calculi, it will cause various secondary damages to the ureter, and the degree of damage depends on the size, shape, location and medical history of the calculi. The main secondary lesions were urinary tract obstruction, secondary infection and epithelial injury.

(1) Urinary tract obstruction

Ureteral lumen stenosis, as well as physiological stenosis, small stones can easily stay in these narrow parts and cause incarceration. Ureteral stones rarely cause complete obstruction. Because stones are generally irregular jujube stones, urine can generally be bypassed. According to different height, the total length of adult ureter is about 22 ~ 30 cm. The diameter of ureter is different, and there are three kinds of physiological strictures in anatomy: the inner diameter of ureteropelvic junction is about 2 mm; The inner diameter of ureter passing through iliac vessels is about 4 mm; The inner diameter of the junction of ureter and bladder is about 3 ~ 4 mm, and the narrowest part of ureter is the part that enters bladder through the submucosal passage of bladder, that is, the wall section of ureter and bladder. The ureter can be divided into abdomen and pelvis, the abdomen refers to the place from the renal pelvis to the iliac blood vessels, and the pelvis refers to the place from the iliac blood vessels to the bladder. The above three strictures are the places where urinary calculi are most prone to obstruction and incarceration in the descending process. But generally speaking, stones often stay within 5 cm of the lower ureter. Partial obstruction of stones will cause dilatation of renal pelvis and ureter near stones. If discharged in a short time, it will not cause any harm. If the retention time is too long, the smooth muscle of the early dilated part of the ureter will be compensatory hyperplasia and hypertrophy, and the ureter cavity will gradually expand, stretch and twist, and the tube wall will become thinner; Late pathological changes will gradually involve the kidney, leading to hydronephrosis of renal pelvis and calyx. If the time is too long, it will cause irreversible renal function damage like complete obstruction.

(2) Secondary infection

It is easy to occur when stones are partially or completely blocked. Because stones damage the ureteral mucosa and even cause ulcers, which reduces the resistance of local tissues to infection, ureteritis and periureteritis often occur in the affected parts. Due to the proliferation and thickening of inflammatory fibers in the ureteral wall, the lumen stenosis is serious, and the inflammatory adhesion between stones and mucosa makes it more difficult to discharge stones. In the later stage, with the aggravation and spread of inflammation, there may be severe pyelonephritis, which will accelerate the process of renal damage. In a few patients, due to severe suppurative infection, stones can penetrate the ureteral wall and be discharged out of the cavity, and urine extravasation can occur.

(3) epithelial injury

The movement of stones and the peristalsis of the tube wall are more likely to directly damage the ureteral mucosa, leading to congestion, edema, necrosis and shedding of the mucosal epithelium, forming ulcers and inflammatory fibrosis, thickening the tube wall and narrowing the lumen.