Hydronephrosis

This term is used to describe a dilated renal pelvis. It is also used to describe a dilated pelvis and ureter, although technically this is hydronephroureterosis. A hydronephrosis may be obstructive or non-obstructive.

Obstructive hydronephrosis

A ureter may be obstructed in four different ways (Fig. 19.7):

1. A mass within the lumen: A ureteric stone, blood clot or sloughed necrotic papilla may all get stuck within the ureter and cause obstruction.

2. Narrowing of the wall: A stricture may result from previous surgery such as ureteroscopy or damage at open surgery (e.g. anterior resection). Fibrotic narrowing is seen as a result of chronic inflammatory conditions, such as renal tuberculosis and schistosomiasis. A tumour is a cause of "mass within the lumen" and failure of normal ureteric peristalsis in the region of the PUJ leads to classical PUJ obstruction.

3. Pressure from outside compressing the ureter: Metastatic lymph nodes or retroperitoneal fibrosis (RPF) can result in ureteric obstruction.

4. A mass at the end of the ureter obstructing outflow of urine: A bladder carcinoma or prostate carcinoma infiltrating the trigone of the bladder can occlude the ureteric orifice. In women, carcinoma of the cervix can cause a similar effect. A chronically distended bladder (due to benign prostatic hypertrophy (BPH) or urethral stricture) can cause backpressure and hydronephrosis.

External compression ^

Stricture

External compression ^

Stricture

Bladder cancer obstructing ureteric orifice

Figure 19.7. (a) Kidney showing sites of possible ureteric obstruction and (b) kidney with duplex ureters.

Bladder cancer obstructing ureteric orifice

Figure 19.7. (a) Kidney showing sites of possible ureteric obstruction and (b) kidney with duplex ureters.

Non-obstructive hydronephrosis

A dilated renal pelvis and ureter may be chronically distended rather than obstructed (e.g. VUR may produce a distended system). Following corrective surgery for a PUJ obstruction the hydronephrosis may seem unchanged, but prompt drainage will be demonstrated by renography. The congenital megaureter is another example of a dilated, but not obstructed ureter.

Ultrasonography will confirm the presence of a dilated system and an IVU may reveal the level of the obstruction. Isotope renography, using MAG 3, gives a functional measure of renal excretion and drainage and is an accurate way of quantifying obstruction, but will not show the anatomical level of obstruction.

If an obstructive cause is suspected, a cystoscopy and retrograde ureteropyelogram (RGPG) will confirm the site of obstruction and often gives an indication as to the cause of the obstruction. If an RGPG fails, percutaneous nephros-tomy and antegrade ureterography usually demonstrates the level and cause of obstruction reliably.

At the time of imaging it is possible to place an indwelling ureteric stent. This is a hollow plastic tube with a draining hole along its length and ends that curl up, hence the name double pigtail or double J® stent. This may be placed retrogradely or antegradely along the ureter from the renal pelvis to the bladder, effectively bypassing the obstruction. Further treatment will depend on the cause of the hydronephrosis.

Alternatively, in some circumstances CT and magnetic resonance imaging (MRI) scanning may be used to diagnose the site and cause of an obstruction, particularly for conditions in and around the kidney.

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