Hydronephrosis

Question 1

What is the blood supply of the kidneys?

Answer 1

• The renal artery supplies blood to the kidney and proximal ureter, as well as small branches off the gonadal artery and aorta
• The middle ureter is fed by blood vessels from the common iliac artery, internal iliac, superior vesical, middle rectal, and inferior vesical arteries
• Proximal to the iliac artery, the blood supply comes medially distal to the iliac artery; it comes laterally

Question 2

What are the significant regions of the ureter when it comes to obstruction?

Answer 2

• It is important to understand the blood supply of the ureter when contemplating surgery on it
• The ureter has a variable diameter of approximately 5-10mm but has 3 distinct areas of narrowing:
  
  • the ureteral pelvic junction (2-3mm)
  • the region over the iliac vessels (4mm)
  • and the ureteral vesical junction (2-4mm)
• Stones, which typically form in the kidney, tend to hang up these areas of narrowing, causing obstruction and renal colic

Question 3

What are the three major categories of acute renal failure?

Answer 3

• Acute renal failure can be sub-categorized into 3 groups: prerenal, renal, and postrenal
• This lecture will deal with postrenal obstruction

Question 4

Define the following terms: hydronephrosis, obstructive uropathy, and obstructive nephropathy.

Answer 4

• Hydronephrosis: is a descriptive term referring to dilatation of the renal pelvis and calyces
• Obstructive Uropathy: is structural impedence to the flow of urine anywhere along the urinary tract
• Obstructive Nephropathy: refers to damage of the renal parenchyma resulting from obstruction of urine flow anywhere along the urinary tract

Question 5

What is the presentation of acute renal obstruction?

Answer 5

• Patients with acute obstruction typically present with:
  
  • flank pain
  • lower abdominal pain
  • groin pain
  • penile or testicular pain
  • inner thigh pain
  • nausea
  • vomiting
  • when infection is present:
    
    • fevers and chills
• Serum studies may show azotemia and hyperkalemia
• Hematuria, proteinuria, and pyuria may be present in the urine. With bilateral obstruction patients are anuric.

Question 6

What are the phases of obstruction?

Answer 6

• Acute obstruction has 3 phases:
  
  • Phase I: renal blood flow and ureteral pressure rise (1-1.5 hours)
  • Phase II: decreased renal blood flow and increased ureteral pressure (1.5-5 hours)
  • Phase III: decreased renal blood flow, decreased ureteral pressure (greater than 5 hours)

Question 7

Describe the process of recovery after kidney damage from obstruction.

Answer 7

• Damage to the kidney occurs gradually over a period of 6 weeks
• Studies in dogs have shown that with unilateral ureteral obstruction of 7 days, full recovery is possible within 2 weeks
• Fourteen days of unilateral ureteral obstruction results in permanent decline in renal function to 70% of control levels with 3-6 months necessary for recovery time
• After 4 weeks of unilateral ureteral obstruction, some recovery is possible
• After 6 weeks, no recovery is possible
  
  • This is an important point when managing ureteral stones as patients can safely be followed for up to a week, allowing them time to spontaneously pass the stones

Question 8

What are the gross and histologic findings of an obstructed kidney?

Answer 8

• Grossly obstructed kidneys become hydronephrotic with compression of the papillae, caliceal blunting, and thinning of the parenchyma
• Histologically, there is dilatation of the tubules and glomerular hyalinization

Question 9

What is the presentation of chronic renal obstruction?

Answer 9

• Patients with chronic obstruction typically present with:
  
  • weight gain
  • edema
  • malaise
  • uremia (resulting in mental status changes, tremors and bleeding)
  • and typically in males
  • may have a weak or intermittent stream
  • overflow incontinence
  • polyuria secondary to a poor concentrating ability

Question 10

What are the diagnostic tests for renal obstruction?

Answer 10

• Obstruction is typically diagnosed by a variety of radiographic studies:
  
  • Intervenous urogram / Pyelogram (IVU or IVP), which typically shows a delayed nephrogram, delayed pyelogram, hydronephrosis, columning, and in high-grade obstruction, forniceal rupture
  • Ultrasonography shows dilated collecting system and echoic central areas in the normally eugenic renal sinus with parenchymal thinning
  • Computerized tomography (typically shows findings similar to ultrasonography)
  • Diuretic renography shows an elevated T1 half (clearance of tracer after Lasix) with less than 10 minutes considered normal, 10-20 min. elevated, greater than 20 min. indicative of obstruction
  • Whitaker test is the gold standard for determining obstruction. Percutaneous infusion of saline in contrast into the renal pelvis at 10ml/minute shows a pressure gradient typically of less than 15cm of water. If the pressure gradient is greater than 22cm of water, this is indicative of obstruction

Question 11

What is post obstructive diuresis?

Answer 11

• Post obstructive diuresis refers to polyuria after release of bilateral obstruction
• It is the normal physiologic release of urea, sodium and water
• In pathologic conditions, there is impaired concentrating ability and sodium resorption
• If urine output is >200ml/hour for 2 hours, or the urine osmolality is low, or the patient is unable to drink, urine should be replaced at a rate of one half cc of D5.45 normal saline per cc of urine

Question 12

What is the presentation of a combination of obstruction and infection? What is the treatment?

Answer 12

• The combination of obstruction and infection can be deadly
• Typically, these patients have flank pain, fevers, chills, leukocytosis, pyuria and bacteri urea
• Urine enters the blood stream via pyelolymphatic and pyelovenous back flow
• Forniceal rupture may lead to a perinephric abscess, typically contained within Gerota’s fascia
• Patients with obstruction and infection should immediately have their blood and urine cultured
• Broad-spectrum intervenous antibiotics should be started and the obstructed kidney or bladder should be drained with percutaneous nephrostomy tubes, ureteral stents, or urethral catheters

Question 13

What is the presentation and etiology of urolithiasis?

Answer 13

• Urolithiasis occurs with supersaturation, crystallization and aggregation
• When the solubility product (Ksp) is reached, crystallization occurs
• More important is the formation product as urine is metastable with respect to calcium oxalate due to factors such as inhibitors, matrix, and nucleation
• Intrinsic factors causing urolithiasis are hereditary factors, age, and sex
• Extrinsic factors include geography, water intake, diet and occupation
• The etiology of stones in 95% of cases can be determined by a metabolic stone evaluation, which includes two 24-hour urine collections and blood tests

Question 14

What are the imaging findings of urolithiasis?

Answer 14

• 75% of stones are formed of calcium oxalate and calcium phosphate
  
  • These tend to be radiopaque in nature and typically are caused from hypercalciuria, hyperoxaluria and hypocitraturia
• Magnesium ammonium phosphate (struvite) stones are the result of infection with urea-splitting bacteria and compose 8% of kidney stones
  
  • These stones are radiopaque
• Uric acid stones occur in 6% of the population
  
  • They are radiolucent and form in acid (pH5) urine
  • Cystine stones are rare (2% of stones) and are secondary to homocystinuria

Question 15

What are the different types of stones and what are the diagnostic findings and predisposing factors?

Answer 15

• Calcium oxalate with or without calcium phosphate
  
  • 75%
  • Opaque
    
    • Hypercalciuria
    • Hyperuricosuria
• Pure calcium phosphate
  
  • 9%
  • Opaque
    
    • Renal tubular acidosis
    • Medications: Diamox, Calcium, Vitamin D
• Magnesium ammonium phosphate (struvite)
  
  • 8
  • Opaque
    
    • Infection with urea-splitting bacteria
• Uric acid
  
  • 6%
  • Lucent
    
    • Hyperuricosuria
    • ​Acid urine
    • ​Low urine volume
• Cystine
  
  • 2%
  • Opaque
    
    • Cystinuria

Question 16

What is the definition of hypercalcuria, and what are the three major causes?

Answer 16

• Most stone formation is due to underlying metabolic abnormalities. Hypercalciuria refers to elevated levels of calcium in the urine (greater than 250mg/24 hours). There are 3 causes of hypercalciuria:
  
  • Resorptive hypercalciuria occurs when calcium is resorbed from bones
    
    • This condition typically occurs with hyperparathyroidism and patients have elevated serum calcium levels
    • The treatment for this condition is parathyroidectomy
  • Absorptive hypercalciuria is the most common cause of hypercalciuria and occurs from increased absorption of calcium in the gut
    
    • This is typically treated with thiazide diuretics
  • Renal leak hypercalciuria is due to excess leakage of calcium from the kidney into the urine and is treated with thiazide diuretics

Question 17

What is the definition of hyperoxaluria?

Answer 17

• (greater than 40mg/24 hours) refers to too much oxalate in the urine
• In some rare cases, it can be caused by a primary liver disease (oxalosis), but is more commonly due to increased absorption in the bowel

Question 18

What is the definition of hypocituria?

Answer 18

• (less than 320ml/24 hours) refers to low citrate levels in the urine
• Citrate inhibits kidney stone formation and can be treated with diet, dietary modifications (lemonade), or potassium citrate tablets

Question 19

What is the definition of hyperuricosuria?

Answer 19

• (greater than 600ml/24 hours) refers to excessive uric acid levels in the urine
• This can be seen in gout or in patients with excessive purine (meat, fish, etc.) intake

Question 20

What is the definition of struvite stones?

Answer 20

• Caused by urease producing bacteria (proteus, klebsiella, pseudomonas, staphylococcus, etc.)
• Urease producing bacteria use urease, an enzyme, to supply their demand for nitrogen, which they obtain for the urine
• Urea represents the principal excretory nitrogenous product in the urine
• Bacteria split urea with urease to produce ammonia (NH3)
• Calcium, magnesium, and phosphate, which are normally present in the urine combine with ammonium (NH4+) at pH greater than 7.2 to form struvite stones (Magnesium ammonium phosphate stones)

Question 21

What is the definition of cystinuria?

Answer 21

• Refers to the inborn error of transport of dibasic amino acids:
  
  • cystine
  • ornithine
  • lysine
  • arginine
• Excessive secretion of cystine results in supersaturation and stone formation
• Cystine precipitates when the cystine concentration exceeds 250ml/L
• The treatment for cystine stones is alkalinization with potassium citrate (K-citrate) and Thiola, a reducing thiol compound
• Thiola binds with cysteine to form a mixed disulfide bond (Thiola-cysteine) and is soluble

Question 22

What is the mainstay of kidney stone prevention?

Answer 22

• The mainstay of kidney stone prevention, however, is a high-fluid (3-4 liters/day), low salt diet
• Patients with recurrent stones should have yearly X-rays, physical exams, and 24-urine collections to monitor for new stone formation