Obstructive Uropathy

The term obstructive uropathy refers to a blockage preventing urine flow through the ureters, bladder and urethra. 

 

Anatomy of the Urinary Tract

The key structures of the urinary tract are the:

  • Kidneys
  • Ureters
  • Bladder (with the detrusor muscle)
  • Urethra
  • Internal urethral sphincter (smooth muscle under autonomic control)
  • Prostate (in males)
  • External urethral sphincter (skeletal muscle under voluntary control)

 

It is worth being familiar with the basic anatomy of the kidney. From the outside in, the basic structures are the:

  • Cortex
  • Medulla
  • Pyramids and columns
  • Major and minor calyx (pleural: calyces)
  • Renal pelvis
  • Pelviureteric junction (PUJ)
  • Ureter

 

Obstructive Uropathy

Obstruction leads to back-pressure in the urinary system, causing areas proximal to the site of obstruction to become swollen with urine. For example, obstruction at the opening of the ureters in the bladder, from a bladder tumour, will result in swelling of the ureter and kidney on that side. Swelling of the kidney is known as hydronephrosis. Vesicoureteral reflux (VUR) refers to urine refluxing from the bladder back into the ureters.

When obstructive uropathy leads to an acute reduction in kidney function, it is referred to as a “post-renal” acute kidney injury (AKI). This is different from “pre-renal” AKI, which is caused by hypoperfusion of the kidneys (e.g., due to dehydration, sepsis or acute blood loss), and “renal” AKI, which refers to damage within the kidney itself (e.g., due to glomerulonephritis or nephrotoxic medications).

TOM TIP: Whenever someone asks you the cause of renal impairment, always answer: “the causes are pre-renal, renal or post-renal”. This will impress them and allow you to think through the causes more logically.

 

Presentation

An upper urinary tract obstruction (i.e. in the ureters) presents with:

  • Loin to groin or flank pain on the affected side (due to stretching and irritation of ureter and kidney)
  • Reduced or no urine output
  • Non-specific systemic symptoms, such as vomiting
  • Impaired renal function on blood tests (i.e. raised creatinine)

 

Lower urinary tract obstruction (i.e. in the bladder or urethra) presents with:

  • Difficulty or inability to pass urine (e.g., poor flow, difficulty initiating urination or terminal dribbling)
  • Urinary retention, with an increasingly full bladder
  • Impaired renal function on blood tests (i.e. raised creatinine)

 

An ultrasound of the kidneys, ureters and bladder can be helpful in diagnosing obstructive uropathy.

TOM TIP: “Loin” is a vague term that can be confusing and does not describe a specific location. Sometimes “loin” is used to describe the sides of the body between the lower ribs and pelvis, although “flank” is also used for the same area. “Loin” is also used to describe the side of the lower back, where the kidneys are situated; as well as the lumbar region of the back, the groin and the area around the hips. “Loin to groin” pain usually refers to pain that circles from the kidney area at the back, round the sides and down into the groin. “Loin to groin” pain is a sign of pathology in the ureter and kidney on that side, such as kidney stones or pyelonephritis. The “renal angle”, also called the “costovertebral angle”, refers to the angle formed by the twelfth rib and vertebral column at the back. The lower part of the kidneys are at the renal angle. Tenderness in the renal angle suggests kidney pathology.

 

Common Causes

Upper urinary tract obstruction:

  • Kidney stones
  • Tumours pressing on the ureters
  • Ureter strictures (due to scar tissue narrowing the tube)
  • Retroperitoneal fibrosis (the development of scar tissue in the retroperitoneal space)
  • Bladder cancer (blocking the ureteral openings to the bladder)
  • Ureterocele (ballooning of the most distal portion of the ureter – this is usually congenital)

 

Lower urinary tract obstruction:

  • Benign prostatic hyperplasia (benign enlarged prostate)
  • Prostate cancer
  • Bladder cancer (blocking the neck of the bladder)
  • Urethral strictures (due to scar tissue)
  • Neurogenic bladder

 

Neurogenic Bladder

Neurogenic bladder refers to abnormal function of the nerves innervating the bladder and urethra. It can result in overactivity or underactivity in the detrusor muscle of the bladder and the sphincter muscles of the urethra.

Key causes are:

  • Multiple sclerosis
  • Diabetes
  • Stroke
  • Parkinson’s disease
  • Brain or spinal cord injury
  • Spina bifida

 

Neurogenic bladder can result in a variety of problems, including:

  • Urge incontinence
  • Increased bladder pressure
  • Obstructive uropathy

 

Management

Management involves removing or bypassing the obstruction. 

A nephrostomy may be used to bypass an obstruction in the upper urinary tract (e.g., a ureteral stone). A nephrostomy involves surgically inserting a thin tube through the skin at the back, through the kidney and into the ureter. This tube allows urine to drain out of the body, into a bag.

A urethral or suprapubic catheter may be used to bypass an obstruction in the lower urinary tract (e.g., a urethral stricture or prostatic hyperplasia). A urethral catheter is a tube, inserted through the urethra, into the bladder. A suprapubic catheter is a tube, inserted through the skin just above the pubic bone, directly into the bladder.

 

Complications of Obstructive Uropathy

  • Pain
  • Acute kidney injury (post-renal)
  • Chronic kidney disease
  • Infection (from bacteria tracking up urinary tract into areas of stagnated urine)
  • Hydronephrosis (swelling of the renal pelvis and calyces in the kidney)
  • Urinary retention and bladder distention
  • Overflow incontinence of urine

 

Hydronephrosis

Hydronephrosis is swelling of the renal pelvis and calyces in the kidney. This occurs due to obstruction of the urinary tract, leading to back-pressure into the kidneys.

Idiopathic hydronephrosis is the result of a narrowing at the pelviureteric junction (PUJ) – the site where the renal pelvis becomes the ureter. This narrowing may be congenital or develop later. It can be treated with an operation to correct the narrowing and restructure the renal pelvis (pyeloplasty).

Typical presenting features of hydronephrosis are vague renal angle pain and a mass in the kidney area. It may be seen on an ultrasound, CT scan or intravenous urogram (x-ray with IV contrast collecting in the urinary tract).

Treatment of hydronephrosis involves treating the underlying cause. If required, pressure can be relieved with either:

  • Percutaneous nephrostomy – inserting a tube through the skin and kidney into the ureter, under radiological guidance
  • Antegrade ureteric stent – inserting a stent through the kidney into the ureter, under radiological guidance

 

Last updated May 2021