Any constraint impeding urine passage through the urinary tract distal from the renal pelvis causes hydroureter, i.e., overfilling of the ureter with urine and subsequent distention. While most hydroureter are obstructive, non-obstructive conditions may trigger that same condition.
Sudden obstruction of the urinary system is normally associated with considerable pain. People may present to the emergency department with ureteral or renal colics particularly in cases of calculi locking in the ureter and completely blocking urine passage through it. However, certain anatomical malformations, prostatic hypertrophy, neoplasms and other conditions that provoke only partial urinary tract obstruction or that develop slowly do generally not cause painful hydroureter and hydronephrosis. Here, tissues may adapt to increased pressures. Of note, reduction of urine drainage by partial constraints may become painful if diuresis is induced either involuntarily or on purpose.
Tenderness and pain may be experienced in the lower back, in the respective side or in pelvic and genital regions. But although the site of pain may hint at an upper urinary tract (kidneys, upper ureter) or lower urinary tract (lower ureter, urinary bladder, urethra) obstruction, pain radiates and its location is not diagnostic.
Diagnosis of chronic hydroureter and hydronephrosis may be further complicated by the fact that impairment of renal function is compensated until less than 40% of all nephrons remain operative. If symptoms manifest, changes in urine quantity may be most easily noted. They are more common in patients suffering from lower urinary tract obstruction. Anuria, oliguria and polyuria may all indicate urine backlog and renal compromise, whereby anuria may be triggered by complete bilateral obstruction and polyuria is typically associated with acute renal failure. Hematuria is common.
Anatomic malformations are usually diagnosed prenatally by means of sonographic examinations. There is, however, no consensus regarding post-natal follow-ups and possible intervention, and although most cases of fetal hydroureter are benign, pediatric patients may indeed develop the above described symptoms of acute or chronic hydroureter and hydronephrosis .
From patients suspicious for urinary tract obstruction, a detailed medical history should be obtained. Previously detected urolithiasis, prostatic hyperplasia or cancer may constitute important hints as to possible causes for hydroureter and hydronephrosis. Patients may have observed alterations in urine quality and quantity and should be questioned accordingly.
After clinical examination, blood and urine samples should be obtained for laboratory analyses. An infection is usually indicated by elevated serum levels of inflammatory parameters and pyuria. Hematuria may also be caused by infection, but furthermore by urolithiasis - the most common trigger of this finding in hydroureter patients -, intrinsic tumors of the urinary tract or infiltrating neoplasms. Blood urea nitrogen and creatinine levels should be measured to assess renal function. Serum electrolyte concentrations have to be studied since imbalances, particularly hyperkalemia, may be life-threatening.
While the aforementioned tests may prompt a strong suspicion for urinary obstruction, this diagnosis should be confirmed and specified by applying diagnostic imaging techniques. While ultrasonography is often the method of choice to detect and follow-up on developmental anomalies, it does not compare to computed tomography scans and magnetic resonance imaging in achieving precise diagnoses in symptomatic patients   . Contrast-enhanced techniques like intravenous or retrograde pyelography may further improve sensitivity and specificity of the aforementioned techniques, but also of plain radiography. With regards to postnatal management of prenatally diagnosed malformations, additional methods like voiding cystourethrography, renal scintigraphy, and magnetic resonance pyelography may supplement the above mentioned traditional sonography .
Pharmacological treatment may relieve pain and prevent infection, but is usually not sufficient to remedy the cause of urinary tract obstruction. Additionally, patients suffering from uric acid stones or, to lesser degrees, from calcium oxalate and cystine calculi may benefit from urine alkalinization.
Most hydroureter patients require at least minimally-invasive surgical care. The specific procedure largely depends on the underlying disease and on the location of the constraint. Any sign of infection, particularly in immunodeficient patients, requires an urgent intervention to avoid sepsis.
Prenatal surgery is possible and may be indicated in cases of oligohydramnios, but evidence regarding long-term benefits is still lacking. Thus, at present, this procedure is the subject of controversial debate .
Prognosis of hydroureter largely depends on the underlying disease. If the condition can be remedied within a few weeks, the probability for complete renal functional recovery is good. However, prolonged hydronephrosis may lead to renal atrophy and chronic renal failure. If this condition affects both ureters and kidneys and adequate treatment is not provided, it may be life-threatening.
Backlog of urine increases the risk for infection, urolithiasis and formation of scar tissue. These may impede regeneration of physiological urine passage even after the primary constraint has been eliminated.
As has been indicated above, different causes account for hydroureter and hydronephrosis in distinct age groups.
Anatomical malformations are the most frequent triggers of these conditions in children. Actually, such abnormalities form during intra-uterine development and may be detected prenatally. Most common findings include vesicoureteral reflux, ureterovesical junction obstruction, posterior urethral valves and uterocele . They may or may not require post-natal medical intervention.
While most processes that trigger pathological hydroureter impair urine passage through the upper parts of the urinary tract, pathologies affecting the urinary bladder or the urethra may provoke backlog of urine up to ureters and kidneys. In these cases, both ureters and kidneys are overfilled with urine and dilated.
Physiological hydroureter are observed in pregnant women and result from the growing uterus compressing the urinary tract or from increased serum progesterone levels that cause relaxation of the smooth musculature forming the ureteral wall.
Hydroureter may be diagnosed in patients of any age. However, developmental defects usually manifest in early childhood and any other physiological or pathological leading to ureteral dilation is more prevalent among adults. Gender distribution has to be considered taking into account the age of the patients. With regards to young adults in fertile age, women are affected more frequently than men. This fact presumably results from pregnancy as a risk factor for hydroureter and hydronephrosis. Both females and males may develop urolithiasis and urogenital tumors, but the high incidence of prostatic hypertrophy and neoplasm significantly increases the share of males among hydroureter patients aged 60 years and older.
Distinct anatomical and functional conditions may impair urine flow through the urinary tract. Urine backlog leads to overfilling and distension of more proximal structures, namely of ureters and kidneys. Increased ureteral pressure impedes urine drainage from the renal pelvis and consequently interferes with glomerular filtration and tubular function. Pyelorenal backflow may be observed. In this context, excretion of metabolic products, maintenance of electrolyte balance and blood pressure may be significantly disturbed.
In most cases, hydroureter and hydronephrosis can be remedied and the aforementioned processes revert to their physiological state, even though this may occur in a delayed manner. The risk of permanent renal damage increases with duration of hydroureter and hydronephrosis. Renal atrophy, for instance, is irreversible. It has been estimated that irreversible tissue damage occurs after about six weeks of continuously increased ureteral and renal pressure . Therefore, this period of time is considered to mark transition from acute to chronic hydroureter.
Patients with a known predisposition for urolithiasis may benefit from dietary adjustments. No measures can be recommended to avoid other causes of hydroureter.
Any obstruction of the urinary tract that impairs urine passage leads to dilation of those parts of this organ system that are located more proximally. In this context, any constraint affecting the urinary system distal from the renal pelvis causes ureteral urine backlog and distention of this structure. This condition is designated obstructive hydroureter. It is by far the most common pathological form of hydroureter and is frequently encountered in distinct diseases affecting the retroperitoneal space, the abdominal cavity or the pelvic region. Dependent on the precise location of the obstruction or the overall size of a large, space-occupying process, a patient may be diagnosed with unilateral or bilateral obstructive hydroureter.
Hydroureter is not necessarily a pathologic condition. Indeed, it is commonly encountered in pregnant women and here, it is considered physiological. On the one hand, the growing uterus may temporarily compress one or both ureters and in this case, hydroureter etiology corresponds to that of the above described obstructive hydroureter. On the other hand, altered hormone levels in pregnant women, mainly increased serum progesterone concentrations, may significantly relax the muscular tissue of the ureter's tunica muscularis and thereby cause ureter dilation . The latter may serve as an example for non-obstructive hydroureter and can be observed in up to 80% of pregnant women and those females who recently gave birth . Because it does not necessarily occur bilaterally, differentiation between physiological and pathological may pose a diagnostic challenge .
Hydroureter may be diagnosed in patients of all ages. Anatomic abnormalities resulting in reduced urine passage through the urinary tract usually manifest in early childhood. They account for the majority of hydroureter cases diagnosed in pediatrics. Urolithiasis is the most common trigger of hydroureter in adults of any age, while prostatic hypertrophy and neoplasms are frequent causes of this pathology in the elderly.
Urine is produced in the kidneys, subsequently passes ureters, urinary bladder and urethra. If an obstruction of any type impairs urine passage through these organs, backlog of urine will occur proximal to this constraint. Thus, any condition impeding urine passage distal of the kidneys does affect one or both ureters. If an ureter overfills with urine and dilates, this condition is called hydroureter.
In most cases, this condition is caused by obstruction of the urinary tract or by compression from the outside. In detail, the following pathologies may account for hydroureter:
Of note, hydroureter are considered physiological in pregnant women if caused by elevated serum progesterone levels or by compression of the urinary system by the growing uterus.
While acute obstruction of the urinary tract is usually very painful, this may not be the case if slowly-developing processes like prostatic hypertrophy or tumors account for this condition. If pain is experienced, it may be noted in the lower back, in either of both sides, in pelvic or genital regions.
Some patients note changes in urine quantity. Others report to observe blood particles in their urine.
The patient's medical history is of utmost importance to identify the cause of a possible hydroureter. In this context, any information regarding previously detected calculi, prostate enlargement or cancer may be very helpful. Diagnosis itself, however, is based on blood and urine analyses and imaging techniques. The former will allow for an assessment of renal function and possible electrolyte imbalances and may indicate infection. The latter is applied to localize the constraint.
Anatomic malformations are often detected during prenatal ultrasound examinations.
Treatment largely depends on the underlying condition. In many cases, surgical interventions will be necessary to resolve the causative obstruction of the urinary tract. Physical destruction of calculi by means of lithotripsy may be an alternative to surgery. Drug therapy is often limited to pain relieve and prevention of infection.
If urine flow can be re-established within six weeks after onset of hydroureter, prognosis for full recovery of renal function is good.