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 (Fig.below). 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.
ultrasound images Ultrasound images of Moderate to marked hydronephrosis of the right kidney secondary to a pelvic lesion. The cortical thickness is normal suggesting the obstruction is relatively recent and that relief of obstruction should produce a significant improvement in renal function.
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.
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