Hydronephrosis

Hydronephrosis is an aseptic dilatation of the kidney due to a partial or complete obstruction to the outflow of urine.

Unilateral hydronephrosis

Unilateral hydronephrosis (Table 64.3) is caused by some form of ureteric obstruction, with the ureter above the obstruction being dilated.

Bilateral hydronephrosis

Bilateral hydronephrosis is usually the result of urethral obstruction, but it may be caused by one of the lesions described above occurring on both sides.

When due to lower urinary obstruction, the cause may be:

1. Congenital:

(a)  congenital stricture of the external urethral meatus or, rarely, phimosis;

(b)  congenital valves of the posterior male urethra or congenital contracture of the bladder neck.

2. Acquired:

(a)  benign prostatic enlargement or carcinoma of the prostate; postoperative bladder neck scarring;

(b)  inflammatory or traumatic urethral stricture, phimosis.

Urethral obstruction tends to lead to hypertrophy of the bladder detrusor muscle which can lead to obstruction to the ureters in the intramural part of their course.

Pathology

In a kidney with an extrarenal pelvis, the dilatation first affects the pelvis alone (pelvic hydronephrosis). If the obstruction is not relieved, the calyces become increasingly dilated and the renal parenchyma is progressively destroyed by pressure atrophy. In a kidney with a predominantly intrarenal pelvis, destruction of the parenchyma occurs more rapidly. A kidney destroyed by long-standing hydronephrosis is a thin-walled lobulated sac containing pale uriniferous fluid of low specific gravity.

Clinical features

Unilateral hydronephrosis

The female:male ratio of unilateral hydronephrosis (most commonly caused by idiopathic pelviureteric junction obstruction or calculus) is 2:1; the right side is more com­monly affected.

Presenting features include the following.

1. Insidious onset of mild pain or dull aching in the loin. There is often a sensation of dragging heaviness which is made worse by excessive fluid intake. An enlarged kidney may be palpable if the cause is pelviureteric junction obstruction.

2. Attacks of acute renal colic may occur with no palpable swelling.

3. Intermittent hydronephrosis. After an attack of acute renal pain a swelling in the loin is found. Some hours later, following the passage of a large volume of urine, the pain is relieved and the swelling disappears (Dietl’s crisis).

Bilateral hydronephrosis

From lower urinary obstruction. There is little to call attention to the hydronephrosis except, perhaps, a dull loin ache. Symptoms of bladder outflow obstruction predominate. The kidneys are unlikely to be palpable because renal failure intervenes before the kidneys become sufficiently large.

From bilateral upper urinary tract obstruction.

 This is rare compared with unilateral lesions although idiopathic retro­peritoneal fibrosis commonly affects both ureters. Although both systems are obstructed, symptoms may be referred to one side only.

From pregnancy. Dilatation of the ureters and renal pelves occurs early in pregnancy and becomes more marked until the 20th week. The condition results from the effects of high levels of circulating progesterone on the ureteric smooth muscle and it may be considered as part of normal pregnancy. The ureters return to their normal size within 12 weeks of delivery. The main importance of the condition is an increased liability to infection and the possibility that abdominal pain during pregnancy may be erroneously ascribed to ureteric obstruction.

Imaging

Ultrasound scanning (Fig. 64.17) is the least invasive means of detecting hydronephrosis and has been used to diagnose pelviureteric junction obstruction in utero.

Excretion urography is helpful if there is still significant function in the obstructed kidney. The extrarenal pelvis is dilated and the minor calyces lose their normal cupping and become ‘clubbed’. In very advanced cases, the thin rim of poorly functioning renal parenchyma may give a faint nephrogram around the dilated calyces — a ‘soap-bubble’ appearance. If the level of obstruction is in doubt it can help to take follow up films up to 24 hours after the contrast has been injected. The radio-opaque medium slowly diffuses to fill the obstructed system down to the block.

Isotope renography is the most helpful test to establish that dilatation of the renal collecting system is due to obstruction. A substance [usually diethylenetriaminepenta acetic acid (DTPA) or MAG-3] which is filtered by the glomeruli and not absorbed is injected intravenously. The DTPA is labelled with technetium 99m, a gama -ray emitter, so that the passage (of 99mTC labelled DTPA) through the kidneys can be tracked using a gamma camera. 99mTc-DTPA is quickly cleared from a normal kidney but if the ureter is obstructed the marker is trapped in the renal pelvis and will not be washed out even if the flow of urine is increased by administering frusemide (Fig. 64.18).

Very occasionally, doubt still persists and a Whitaker test is indicated. A percutaneous puncture of the kidney is made through the loin and fluid is infused at a constant rate with monitoring of intrapelvic pressure. An abnormal rise in pressure confirms obstruction. Retrograde pyelography (Fig. 64.19) is rarely indicated but will confirm the site of obstruction immediately before corrective surgery.

Treatment

The indications for operation are bouts of renal pain, increasing hydronephrosis, evidence of parenchymal damage and infection. Conservation of renal tissue is the aim; nephrec­tomy should be considered only when the renal parenchyma has been largely destroyed. Mild cases should be followed by serial ultrasound scans and operated upon if dilatation is increasing.

Pyeloplasty

The Anderson—Hynes operation (Fig. 64.20) is appropriate in cases of pelviureteric junction obstruction where a reasonable thickness of functioning parenchyma remains. The affected kidney is displayed and the upper third of the ureter and the renal pelvis carefully mobilised. A renal vein overlying the distended pelvis can be divided but an artery in this situation should be preserved to avoid infarction of the territory that it supplies. The anastomosis is made in front of such an artery using absorbable stitches to avoid calculus formation on the suture line. It is usual to protect the anastomosis with a nephrostomy tube or a ureteric stent.

Endoscopic pyelolysis

Disruption of the pelviureteric junction by a specially designed balloon passed up the ureter and distended under radiographic control has been used to treat idiopathic pelviureteric junction obstruction. The long-term benefit of this and other minimal access techniques still has to be proved.