Obstructive uropathy accounts for about 10% of the cases of Acute kidney injury and 4% of cases of chronic renal failure. Stone disease is one of the most common causes of obstruction. Other causes include malignancy, inflammatory (tuberculosis, schitsosomiasis, amyloidosis, endometriosis ) and congenital (ureteric stricuture, renal cyst, ureterocoele).1
Obstructive uropathy is responsible for a wide range of metabolic and electrolyte abnormalities that may lead to renal failure especially if the obstruction is bilateral. Patients may not be aware or have only mild symptoms if the progress is gradual and may present in frank renal failure
Ultrasonography, CT and CT urography are the gold standard diagnostic tests. US is often the first imaging performed.2
The hallmark of obstruction on US is the presence of hydronephrosis. Prominent anechoic structures in the renal sinus represent a dilated pelvi-calyceal system and calculi may be demonstrated as echogenic focus with or without shadowing.
The degree of hydronephrosis can be estimated visually:
Limitations of US:
The false negative rate with US is as high as 35% in patients with ureteric calculus. Technical limitations such as bowel gas, obesity can hamper imaging.
Mourmouris, Chiras, Paptsoris. Obstructive uropathy- from etiopathology to therapy. World J Nephrol Urol. 2014; 3(1):1-6. PDF
Sameet Rao. Acute obstructive uropathy imaging. Medscape Oct 2015. Link