Hydronephrosis and Hydroureter

Etiology

The cause of urinary obstruction can be broadly classified as intrinsic and extrinsic compression. Causes of intrinsic obstruction include renal stones, malignancy, ureteropelvic junction stenosis, ureteral strictures from prior inflammation, renal cysts, posterior urethral valves, benign prostatic hyperplasia, and neurogenic bladder, etc. Causes of extrinsic compression include pregnancy, peripelvic cysts, retrocaval ureter, malignancy, trauma, retroperitoneal fibrosis, and prostate abscess, etc.

Anatomic abnormalities account for the majority of cases in children. These include urethral valves or stricture, and stenosis at the ureterovesical or ureteropelvic junction.

Epidemiology

The causes and presentations vary among age groups. In newborns and children, structural abnormalities are the primary cause. Yearly, of the estimated 6% total new births worldwide (8 million) born with serious birth defects, as many as 1% of the newborns have congenital defects of kidney and urinary tract.[1] Hydronephrosis is present in a growing number of neonates and infants, most commonly due to ureteropelvic junction obstruction. This is found in up to 1 in 100 live births in the United States and is treated conservatively. In the majority of cases, spontaneous resolution is found by 2 years of age. Less commonly found is vesicoureteral reflux, which accounts for 10%-20% of neonatal and infantile hydronephrosis. Obstruction of ureterovesical junction, posterior urethral valves, and stricture are the other common anatomical abnormalities.

Nephrolithiasis is the most common cause of hydroureteronephrosis in young adults. Approximately 600,000 adults in the US suffer kidney stones per year, affecting nearly 1 in 11 persons. As per the National Health and Nutrition Examination Survey (NHANES), the prevalence of kidney stones is 8.8% in the United States. Among men, it is 10.6% compared to 7.1% in women. White race, obesity, and diabetes are strongly associated with kidney stones.[2]  Prostate hypertrophy and neoplasm, pelvic and retroperitoneal tumors, and renal stones are the more common causes in the elderly population. 

Hydronephrosis is commonly seen in up to 80% of pregnant women. Mechanical compression of the ureters due to the enlarging uterus and the effects of progesterone are thought to be the etiology. It is mostly identified in the second trimester and may persist up to 6 to 12 weeks postpartum. Ureteral stenting is a treatment of choice if patients develop pain and renal failure.[3]

Hydronephrosis is more common in women for the age range 20-60 due to pregnancy and gynecologic malignancy. For the age group greater than 60, it becomes more common in men due to prostate disease and complications.

Pathophysiology

The obstruction of the outward flow of urine leads to an increase in the hydrostatic pressure of the collecting system. This causes an increase in intraglomerular pressure, which will ultimately affect the glomerular filtration rate. The duration and severity of obstruction determine the extent of loss of kidney function. If the obstruction is not relieved, it can lead to kidney scarring and permanent kidney damage with the compromise of glomerular and tubular function. Hence hydronephrosis can be considered acute if kidney function recovers completely when an obstruction is relieved.

In contrast, the kidney function does not recover in chronic hydronephrosis even after the obstruction is relieved. The prolonged obstruction causes a dilated collecting system, compression of papillae, and thinning of parenchyma leading ultimately to cortical atrophy and tubulointerstitial fibrosis. Impairment of sodium reabsorption, disruption of urinary acidification leading to metabolic acidosis, and urinary concentrating ability are some of the physiologic effects.

History and Physical

Infants are typically asymptomatic. However, in more severe cases of congenital hydroureteronephrosis, lack of appetite, and frequent urinary tract infections may be present.[4]

Adults with acute urinary outflow obstruction typically present with constant dull pain thought to be the result of stretching of the renal capsule, with intermittent episodes of severe pain due to genitourinary peristalsis transiently increasing the pressure. Many patients report nausea and vomiting, as well as dysuria or urinary urgency. On exam, these patients have tenderness at the costovertebral angle and often cannot find a position of comfort in the exam room.[5] Patients with more distal obstruction from prostate hypertrophy may report severe lower abdominal pressure and the urge to urinate.[6]

Evaluation

Infants with congenital hydroureteronephrosis should undergo a voiding cystourethrogram to identify patients with vesicoureteral reflux.[7] When presenting with fever, abdominal pain, nausea, or decreased oral intake, a urinalysis should be obtained as these patients are predisposed to urinary tract infections (UTIs). A basic metabolic panel should be ordered to establish a baseline renal function which can be followed to indicate the resolution of hydronephrosis as well as indicate surgical management in patients with worsening renal function.

Adult patients with renal colic due to hydronephrosis should have a basic metabolic panel to evaluate renal function, as well as a urinalysis. Imaging is indicated in these cases based upon their medical history. A computed tomography (CT) scan is highly sensitive and specific when nephrolithiasis or external compression from neoplastic disease is the cause of symptoms. Additionally, CT will be sufficient to evaluate other causes of acute severe flank pain. In patients with a history of frequent kidney stones and symptoms consistent with prior episodes, an ultrasound is sufficient to evaluate for hydronephrosis.[8] Ultrasound is also the imaging modality of choice in pregnant patients with hydronephrosis.[9]

Treatment / Management

In infants with antenatal hydronephrosis, the management approach depends on the persistence of postnatal hydronephrosis, bilateral involvement, and the severity of hydronephrosis. 

Bilateral hydronephrosis is due to obstruction distal to the urinary bladder. Posterior urethral valves are the most common cause of bilateral hydroureteronephrosis. A voiding cystourethrogram should be performed for further diagnosis. A renal pelvic diameter > 15 mm in a newborn is considered severe hydronephrosis. They carry a greater risk of severe renal impairment. Mild to moderate cases resolve by 18 months of age.[10]

Infants with antenatal hydronephrosis are at high risk of developing pyelonephritis with a stronger association in girls.[11] There is no strong evidence to show that infants with severe hydronephrosis will benefit from continuous antibiotic prophylaxis to prevent UTIs.[12](A1)

The cause of hydronephrosis drives specific treatment. A high possibility of renal dysfunction, suspicion for infection leading to severe sepsis, and symptoms of severe pain, nausea, and vomiting warrant urgent treatment of hydronephrosis.

Placement of a urinary catheter is important when lower urinary tract obstruction at the bladder level is highly suspected. Cystoscopy guided ureteral stent placement is a common procedure for various intrinsic and extrinsic causes of hydronephrosis at the ureter level. Fluoroscopy guided percutaneous nephrostomy tube placement is a less invasive procedure performed by interventional radiologists when ureteral stent placement is contraindicated or cannot be done.

Extracorporeal shockwave lithotripsy is used to treat renal stones in the renal pelvis to prevent future hydronephrosis and obstruction. Surgery is also required for some cases with extrinsic compression from pelvic, retroperitoneal tumors, and aortic aneurysms, etc.

Differential Diagnosis

Other conditions to be included in the differential diagnosis include:

• Peripelvic cysts
• Congenital megacalices
• High urine flow
• Pyelonephritis
• Renal calyceal diverticula

Prognosis

Prolonged obstruction from hydronephrosis or hydroureter can lead to irreversible kidney damage from tubular atrophy and interstitial fibrosis. The overall prognosis of renal recovery after the obstruction is relieved depends on the duration and severity of obstruction.

Complications

Urinary tract infection is the most common complication of hydronephrosis. It can further lead to pyelonephritis, infection of the kidney itself. When a chronic obstruction is relieved, patients may develop post obstructive diuresis.