OBSTRUCTIVE UROPATHY PCS DILATATION

PELVICALYCEAL SYSTEM DILATATION AND OBSTRUCTIVE UROPATHY
Not all PCS dilatation, i.e. hydronephrosis, is pathological, or indeed obstructive, that is, there can be dilatation without physiological obstruction. Conversely, not all obstructive uropathy necessarily results in PCS dilatation.

Physiological dilatation
Mild dilatation of the renal collecting system is a common finding, most commonly secondary to an over-distended bladder. Following micturition, the collecting system decompresses and returns to normal. An external renal pelvis is a nonobstructive ‘baggy’ dilatation of the pelvis and can be regarded as a normal variant. The intrarenal collecting system is normal in this situation. Pregnancy is another common cause of mild PCS dilatation, more frequently on the right, particularly in the second and third trimester. This is thought to be due partly to pressure on the ureters from the advancing pregnancy and partly hormonal. It is however wrong to assume that the kidney is not obstructed just because the patient is pregnant. If symptomatic, the suspicion of obstruction in a dilated system is increased, particularly if echoes are present in the PCS.

Obstructive uropathy
Renal obstruction, particularly if long-standing, can irreversibly damage the kidney or kidneys, leading eventually to renal failure. If diagnosed early enough, renal function can be preserved and therefore ultrasound plays a prominent role as one of the first-line investigations in patients with loin pain, renal colic or micturition disorders. In the vast majority of cases, urinary tract obstruction causes dilatation of the collecting system proximal to the site of obstruction. Whether the hydronephrosis is bilateral or unilateral and whether or not it involves the ureter(s) depends on the cause and site of the obstructing lesion. Dilatation of the collecting system may be localized. Sometimes only one moiety of the kidney may be obstructed by a stone or tumour, whilst the rest of the kidney remains normal. In a duplex kidney, dilatation of the upper pole moiety is a common occurrence due to an anomaly at the VUJ, that is, a ureterocoele. If the obstruction is long-standing the renal cortex may atrophy, becoming thin. Normal thickness of cortex is a good prognostic indicator. Function may be assessed with a nuclear medicine (DTPA) scan prior to further management.

Further management of renal obstruction
In the majority of cases the exact level and cause of obstruction are difficult to identify on ultrasound. Confirmation of the cause and identification of the exact level is traditionally best established on IVU; however CT IVU is becoming a rapidly universally adopted first-line investigation. A plain abdominal X-ray is useful in confirming the presence of calculi in the renal tract, but ultrasound may demonstrate stones which are nonopaque on X-ray; CT is probably the best overall test for stone detection. It is important to assess the function of the obstructed side, as a chronic, longstanding obstruction with no residual function cannot be treated, but a kidney which still has function is worth saving. A DTPA scan can assess the relative functions of the obstructed and non-obstructed side.

Percutaneous nephrostomy (the placing of a tube into the PCS to drain the urine) in the case of unilateral obstruction is performed to relieve the obstruction, minimizing damage to the kidney and maintaining renal function and drainage. This may be done under either ultrasound or fluoroscopic guidance or a combination of both. The decision of whether to proceed to nephrostomy or cystoscopic stent will depend upon patient presentation and local factors and policies.

Pyonephrosis
Pyonephrosis is a urological emergency. An obstructed kidney is prone to become infected. High fever and loin pain can suggest obstructive pyonephrosis. Pus or pus cells may also be detected in the urine. Low level echoes can be seen within the dilated PCS on ultrasound, and may represent pus. Sometimes, however, the urine may appear anechoic, despite being infected. The clinical history should help differentiate pyo- from simple hydronephrosis. Percutaneous drainage by ultrasound or fluoroscopically guided nephrostomy is usually necessary, partly as diagnostic confirmation and partly as a therapeutic procedure.

Haemo-hydronephrosis
Blood within the dilated PCS may be due to trauma or other local or semilocal pathological processes such as infection or tumour. It is not usually possible to determine whether obstruction is caused by a blood clot or whether the blood is the result of an obstructing lesion which is also causing bleeding. Renal colic as a result of obstruction by a blood clot in the absence of trauma or blood dyscrasia must naturally be thoroughly investigated to exclude an underlying lesion. Like pyonephrosis, low-level echoes may be seen on ultrasound within the collecting system. Although ultrasonically it is not possible to differentiate pyo- from haemohydronephrosis, the clinical picture can be suggestive of one or the other.