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.