OBSTRUCTIVE UROPATHY (Dr Mohamed Shafik)

Definitions:

Obstructive uropathy:

Resistance to the flow of urine any where along the urinary tract.

Obstructive nephropathy:

Damage to the renal parenchyma as a result of obstructive uropathy.

Hydronephrosis:

Descriptive term referring to dilatation of the pelvis and calyces. It can occur with or without obstruction.

During the past 20 years we have learned that urinary tract dilatation is not the same as UT obstruction.

Clinical presentation: symptoms

Wide range: asymptomatic→ renal colic

Depending on:

Degree: complete or partial

Time interval: acute or chronic

Etiology: intrinsic Vs extrinsic

Laterality: unilateral or bilateral

Signs: Wide range: no signs

- Abdominal mass- Volume overload- Azootemia

Pathophysiology:

Correlation between RBF & UP.

Mediators of acute obstruction.

Clinical implications of pathophysiology for management of obstructive uropathy.

Clinical Implications Of Pathopysiology For Management Of Obstructive Uropathy :

1. Renal colic.

2. Postobstructive diuresis.

3. Prevention of destructive effects of obst. urop. (calcium channel blockers).

4. Hydronephrosis and hypertension.

1. RENAL COLIC

NSAIDs in renal colic:

Advantages:

Provide the same degree of pain relief as narcotics.

Avoid the complications of narcotics (addiction, respiratory depression, mental changes, constipation).

Disadvantages:

Decrease RBF by 35%

Consider renal function

Routes of Administration:

IV, IM, Rectal, Oral, Sublingual.

IV indomethacin is more effective than IM diclofenac.

Rectal route is less effective than parentral route.

Oral diclofenac prophylaxis prevents new episodes of renal colic.

Sublingual piroxicam is as effective as parentral diclofenac.

2. POSTOBSTRUCTIVE DIURESIS

Definition:

Polyuria (> 200 ml/ hour for 24 hours) that occurs after relief of BUO or obstruction of a solitary kidney.

Pathogenesis:

Physiologic: Retained urea, sodium & water.

Pathologic: Impairment of concentrating ability of sodium reabsorption.

Clinical Manifestations:

Edema

Congestive heart failure

Hypertension

Weight gain

Azotemia

Sometimes uremic encephalophathy

Follow up:

Vital signs / 2h.

Urine output / 2h.

Body weight / 24 h.

S. Creatinine / 24 h.

S. electrolytes / 12 h.

Urine electrolytes / 24 h.

Urine osmolarity / 24 h.

Treatment Physiologic Diuresis:

Characters:

It is the most common.

S.creat. & BUN → normal with in 1-2 days

The patient is alert.

Replacement: Oral fluids is sufficient

Treatment Pathologic diuresis:

Characters:

It is less common.

Diuresis persists > 2 days.

S.creat. & BUN remain elevated.

Urine osmolarity remains low.

Patient is usually not alert.

Replacement:

Replace half of urine output until S.creat & BUN become normal.

Supplement with sodium containing IV fluids ( 5 % dextrose in 0.45% saline).

Diagnosis:

IVP: IVP is the gold standard for the detection of ureteral obstruction in patients who have:

1. Normal renal function.

2. No allergies

3. Not pregnant.

(acute obstruction)

4. Obstructive nephrogram.

5. Delay in filling of the collecting system with contrast.

6. Dilatation of the collecting system.

7. Possible fornix rupture with urinary extravasation.

(chronic obstruction)

8. Ureteral dilatation and tortuosity.

9. Standing column of contrast material in the ureter to the point of obstruction.

10. The kidney may demonstrate marked parenchymal thinning.

US:

1. Gray-scale US

2. Diuretic US:

Gray–scale US is done before and after injection of a diuretic

Diagnosis of obstruction is based upon:

Increase of pelvicalyceal diameter after diuretic.

Prolongation of the time taken for the renal collecting system to return to initial diameter.

Criticism: not objective.

Current value: of limited use.

3. Doppler US :

Resisitive index (RI): (Peak systolic velocity diastolic velocity)/ peak systolic velocity.

Relation to obstruction: Value diagnostic of chronic obstruction: > 0.7

Ureteric jets: It is useful only for unilateral obstruction.

Symptomatic side is compared to the normal side for 10-15 minutes after good hydration.

Interpretation: - Complete obstruction: no jets - Partial obstruction: asymetric jets

Criticism: -Technically difficult- Time consuming

Current use: pregnancy

4. Ultrasonographic multivariate scoring system

(Garcia-Pena et al 1997): 7 items

a) Increased echogenicity

b) Parenchymal thickness ≤ 5 mm

c) Contralateral hypertrophy

d) RIR ≥ 1.10

e) ∆RI ≥ 0.07

f) Ureteric diameter ≥ 10mm

g) Aprestaltic ureter

Renogram :

1. Standard diuretic renogram (DR) curve

2. Half time drainage (T ½)“Kass, 1985”

Definition: Time necessary for half of isotopes to be eliminated from the renal pelvis.

Interpretation: < 10 minutes à normal > 20 minutes à obstructed 10 - 20 minutes à equivocal

3. Frusemide minus 15 (F-15) DR

4. Measurement of individual renal function: Progressive deterioration of GFR of the corresponding kidney on subsequent radioisotope studies over time.

Spiral CT:

Acute obstruction: non contrast spiral CT (NCCT): sensitivity-98%, specificity-100%

Potential Pitfalls

Pelvic phleboli: can mimic ureteric stones.

Gonadal vein: can be confused with a dilated ureter.

Disadvantages

1. No evaluation of renal function.

2. No evaluation of urothelium.

3. Expensive.

4. High radiation limiting its use in pregnancy.

5. Needs special training.

6. Not universary available.

Chronic obstruction: contrast-enhanced spiral CT

Limitations:1. Renal impairment.2. Pregnancy.3. Allergy to contrast materials

MRU

Principle: The static column of urine in the dilated urinary tract is easily visualized by T2- weighted MRU as a bright white column, but without injection of radiocontrast material

Indications of T2 MRU:

Contraindications to IVP

Allergy

Pregnancy

Renal impairment

Failure of IVP to reach diagnosis

No excretion

Persistent nephrogram

Poor excretion

No definite diagnosis

Advantages:

1. No injection of contrast materials

2. No exposure to ionizing radiation

3. Noninvasive

4. Can save the patient invasive procedures (ante & retrograde studies).

Diagnostic value in obstructive uropathy:

It can accurately identify:

Presence of obstruction

Degree of dilation

Level of obstruction

Cause of obstruction

Calcular: not accurate

Non calcular: sensitive and specific

Whitaker test

Ante and Retrograde studies