The kidneys have many important functions in the human body. They are the major organs for maintaining fluids and electrolytes balance, they do not only share a great role of acid-base balance in the body, but they also have a vital role in controlling blood pressure and erythropoietin secretions.
During fetal life, the kidneys develop from the metanephric mesoderm up to the distal tubules. The collecting duct, major and minor calyces, renal pelvis, and ureters arise from the ureteric bud which originates from the mesonephric duct during the fifth week of the intrauterine phase.
This explains that the ureteropelvic junction (UPJ) is wholly made by the ureteric bud rather than the fusion of two different mesenchymal tissues.
Ureteropelvic junction obstruction (UPJO) is a well-recognized clinical entity, which results in impaired urine flow from the renal pelvis into the ureter, and if not detected and treated properly, can result in complete loss of the affected kidney. UPJO is mainly a congenital condition that can be detected by antenatal ultrasound during the second trimester.
Ureteropelvic junction obstruction is either a congenital or acquired disease, with the former being the most common etiology.
This is mainly caused by an external compression on the ureteropelvic junction or the proximal ureter.
Ureteropelvic junction obstruction is more commonly seen in the pediatric age group rather than adults, and this anatomical pathology is seen more frequently in boys than in girls, with up to twice the number of cases in males compared to females. The left side is as well affected twice as often as the right side. It is the most common cause for antenatally detected hydronephrosis at around 80% of all causes.
UPJO has an estimated incidence of 1 in 1000 to 1500.
Although it is more common in pediatrics, that does not make it rare to be seen in adults.
The flow of urine from the renal pelvis to the ureter depends on two main factors, firstly, the pressure within the renal pelvis and it’s compliance, which is affected by the produced urine volume, the internal diameter of the UPJ and the collecting system. Secondly, the peristaltic activity of the ureter, which might be affected by the abnormal smooth muscle arrangements, absence, or hypertrophy, in the proximal ureteral walls affecting the peristaltic function. With the latter being the main cause of congenital ureteropelvic junction obstruction.
Less commonly as a congenital cause of UPJO, an accessory renal vessel arising from the renal vessels, aorta, vena cava, or the iliac vessels can interfere with the collecting system.
On the other hand, acquired stenosis of the UPJ due to the previously mentioned causes can result in reactive fibrosis in the affected ureteral segment, and annual strictures might appear.
Most of the UPJOs seen are partial. In this type of obstruction, there is an increase in the production of the vasoactive peptides and cytokines as interleukin (IL)-5 and eotaxin-2 from the urothelium, acting as a chemoattractant for leukocytes, lead to inflammatory cell infiltration. By changing the eicosanoid elaboration in the kidney, the monocytic infiltration is believed to affect the renal blood supply and decrease the total GFR in the affected kidney, however, single nephron GFR will be increased. A good understanding of the pathophysiology of the UPJO might guide the treating physician toward an early intervention to prevent worse outcomes.
In human models, no clear correlation was proven between split renal function and histological findings in the affected population. However, parenchymal damage was observed in severe cases of ureteropelvic junction obstruction. The lack of clear histological findings is considered one of the major obstacles in the clinical assessment of UPJO.
The condition is usually detected during the antenatal scan and is not associated with any antenatal complications.
Pediatric ureteropelvic junction obstruction might be associated with other congenital anomalies as an imperforated anus, multicystic kidney, and ipsilateral ureterovesical reflux, in the similar patients, UPJO should be treated first as distal ureteric diseases are commonly not severe.
In cases of duplex renal system, the lower moiety is more commonly affected, and in this case, ureterovesical reflux is likely to be found and can be diagnosed using voiding cystourethrogram (VCUG).
Common symptoms in older children:
Similarly, adults present with symptoms similar to those in the pediatric age group; however, hematuria and chronic loin pain are commonly seen. Usually, it is associated with increased fluid intake, diuresis, as tea and coffee.
On examination, patients will have chronic loin tenderness in association with hematuria; other signs of pyelonephritis might be present as well, like fever and rigors.
All patients who have symptoms of UPJO should have a full set of blood, including complete blood count, kidney function tests, including creatinine, GFR, and BUN.
Patients will present with high levels of creatinine and decreased GFR, in case of infection, leukocytosis can be seen.
A urine sample should be sent for analysis and culture as recurrent urinary tract infections are commonly seen in these patients.
Hydronephrosis can be detected as an incidental finding on antenatal ultrasound, which might reflect underlying UPJO.
In neonates who were found to have mild to moderate hydronephrosis on an antenatal scan, a follow-up scan should be done after 48 hours, to avoid transient neonatal dehydration period, however, in severe cases, a scan should be performed within the first 48 hours as it might need urgent intervention.
The SFU grading system is used to evaluate the severity of hydronephrosis as follows:
Keep in mind that almost 20% of antenatally detected hydronephrosis is not found after birth.
Poor drainage in pediatric patients less than 18 months might be transient and might improve after a few months spontaneously, given that the patient has normal kidney function. In older patients with split renal function more than 40%, the renal scan should be repeated on 3, 6, and 12 months intervals. Surgery is to be performed if the function is deteriorated.
Surgical intervention is the gold standard treatment of UPJO if indicated.
The indications for surgical treatment include:
Options of Surgery
Medical management is considered to maintain sterile urine, treating urinary tract infections, and assess renal function and the grade of hydronephrosis on a regular basis. However, UPJO cannot be revered using medical management solely.
Finally, in patients with split kidney function less than 10%, asymptomatic patients can be observed. A nephrectomy might be indicated in the case of recurrent urinary tract infection, persistent loin pain, or hematuria.
The differential diagnosis for hydronephrosis at the level of the ureteropelvic junction can be categorized depending on the age of the patient.
Neonatal UPJO and hydronephrosis gradually resolve without any surgical intervention in most of the patients.
There has been shown a strong correlation between the grade of hydronephrosis and the chance of spontaneous resolution, The Society for Fetal Urology suggested grading system for hydronephrosis into four grades, grade I resolves in approximately 50% of patients, and grades II, III, IV hydronephrosis resolve in 36%, 16%, and 3% of cases, respectively.
Complications of UPJO
Complications of Surgical Management of UPJO
Pregnant women are advised to attend their antenatal clinic appointments as UPJO can be diagnosed antenatally, and that would help the interprofessional team to improve the management of the affected individuals. Moreover, patients with symptoms of urinary tract infections should not be neglected and be evaluated promptly.
The management of UPJO should be implemented by an interprofessional team that consists of a urologist, emergency department doctor, radiologist, primary care doctor, and a nephrologist. Moreover, the gynecologist plays a major role in diagnosing the condition antenatally. Urologic nurses should be a part of the team as well, taking care of patients and responding to their needs. Pharmacists are asked to review the patients' medications to avoid any insult to the kidney or drug-drug interactions that might worsen the situation.
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