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Causes and pathogenesis of megoureteritis
Medical expert of the article
Last reviewed: 04.07.2025
The causes of megaureter are congenital anatomical obstruction in the lower part of the ureter, which leads to a violation of the outflow of urine above the obstruction to an increase in intraureteral pressure, a gradual expansion of the lumen of the entire ureter, a violation of its contractility, expansion of the PMS, hydroureteronephrosis with gross irreversible morphological changes in the kidneys.
Similar changes are also caused by the congenital absence of the closure apparatus in the PMS. In these cases, the ureteral orifice is widened and gaping. These changes correspond to neuromuscular dysplasia of the lower ureteral cystoid (achalasia) with subsequent development of damage to all sections of the upper urinary tract (megaureter) and kidney (ureterohydronephrosis).
Neuromuscular dysplasia of the ureter is one of the most common and severe anomalies of the UUT. Despite the large number of works devoted to the study of this anomaly, there is still no consensus on the etiology, pathogenesis and treatment. The diversity of authors' views on these issues is evidenced by the variety of names for megaureter: atony, dalation, ureteral expansion, giant ureter, dysplasia. megaureter, megadolichoureter. hydroureter, achalasia of the ureter, forced ureter, etc.
The causes and pathogenesis of megaureter are explained differently. Some authors believe that the basis of congenital ureter dilation is the insufficiency of the development of the neuromuscular apparatus of the ureter, while others associate the development of megaureter with a functional or organic obstruction localized at the level of the prevesical, juxtavesical or intramural section of the ureter. Recently, neuromuscular dysplasia has been understood as a combination of congenital narrowing of the ureter and its intramural section with neuromuscular dysplasia of the lower cystoid.
Comparing the number of patients with this ureteral malformation detected in a polyclinic setting with the number of patients undergoing treatment in a clinic, we noted that ureteral dysplasia would be detected significantly more often if this category of patients were subjected to a urological examination.
Most often, early stage ureteral dysplasia is detected in children aged 3 to 15 years, mainly at the age of 6-10 years. In adults, late stage ureteral dysplasia is more often observed, complicated by pyelonephritis and renal failure. Females are more often affected by this developmental defect (the ratio of women to men is 1.5:1). Bilateral ureteral dysplasia is more common than unilateral. The defect is localized on the right almost 2 times more often than on the left.
N.A. Lopatkin, A.Yu. Svidler (1971) observed 104 patients and conducted a microscopic examination of 33 resected ureters, as well as ureters taken from corpses during autopsy. The authors found that the number of nerve fibers in the wall of the dysplastic ureter (from the renal pelvis to its prevesical section) is sharply reduced. They are not detected in most preparations. Such changes were found in dysplastic ureters of patients of different ages - from 26 weeks to 45 years. When examining the so-called aganglionic zone in the prevesical section of the ureter, the same basic nerve elements were found as in the ureter of healthy people. This allowed us to assume that the motor ability of the prevesical section of the ureter should not be impaired in case of its dysplasia. Congenital absence of intramural nerve plexuses along the entire ureter, with the exception of the prevesical section, means congenital degeneration of the neuromuscular elements of the ureter and leads to complete exclusion of its walls from contractions.
Megaureter should be considered as a manifestation of dysplasia. In this case, dysplasia may be expressed in the area of only the last or penultimate cystoid. In such cases, we can talk about achalasia of the ureter. This interpretation of the etiology of giant ureters explains the cause of a sharp expansion of the ureter along its entire length or in a limited area and allows us to consider achalasia and megaureter as stages of the same process. It should be noted that the inevitable consequence of achalasia is megaureter, which leads to ureterohydronephrosis.
There are several classifications of ureteral dysplasia, but first of all it should be emphasized that neuromuscular dysplasia of the ureters is a bilateral anomaly.
The consequences of the narrowing of the opening and the intramural section of the ureter, as well as the violation of the tone of the ureter, can be the lengthening and expansion of the cystoids. The expansion of the lower cystoid is called achalasia. In this case, the urodynamics of the upper cystoids is preserved. The involvement of two upper cystoids in the process with an increase in the length of the ureter is called megaureter. In this case, the ureter is sharply expanded and lengthened, its contractile movements are significantly slowed down or absent, the dynamics of emptying are sharply impaired. This allows us to distinguish the following stages of ureteral dysplasia:
- I - hidden or compensated (achalasia of the ureters);
- II - the occurrence of megaureter as the process progresses;
- III - development of ureterohydronephrosis.
Neuromuscular dysplasia of the ureters has no characteristic manifestations and is usually discovered during urinary tract infection.
Anatomical or functional obstruction in the lower part of the ureter leads to stasis of urine above the obstruction, an increase in intraureteral pressure, a gradual expansion of the lumen of the entire ureter, a violation of its contractility, expansion of the pelvioureteral segment, ureterohydronephrosis with gross irreversible morphological changes in the kidneys.
Since the anomaly is bilateral, slow progression of the pathological process in the kidneys leads to the development of severe chronic renal failure. The unfavorable outcome of the disease is explained by the absence of pathognomonic symptoms for this developmental defect and late diagnosis.
Macroscopically, with megaureter, the ureters are sharply dilated, elongated, as a result of which they bend in the retroperitoneal space in the most bizarre way. The diameter of the ureters reaches the diameter of the small intestine. The intramural and juxtavesical sections of the ureters are narrowed over 0.5-1.0 cm to 0.5-0.6 cm, their wall is thickened. In this case, apparently, we should not talk about a true, but about a relative narrowing compared to the sharply dilated overlying sections of the ureter.
[ Megaureter classification
Obstructive megaureter is a consequence of the obstruction of the ureter. It occurs in neuromuscular dysplasia of the ureter, congenital stricture of the ureter and ureteral valve.
The most appropriate classification of megaureter is considered to be the one proposed by N. A. Lopatkin and A. G. Pugachev in 1940, based on indicators of the secretory function of the kidneys, assessed using radioisotope dynamic nephroscintigraphy.
Classification of megaureter by N.A. Lopatkin and A.G. Pugachev according to the degree of renal dysfunction
- Grade I - decrease in renal secretory function by less than 30%.
- Grade II - decrease in the secretory function of the kidney by 30-60%.
- Grade III - decrease in renal secretory function by more than 60%.