Ultrasound images of Non-dilated renal obstruction

Ultrasound images of Obstruction may occasionally be present in the acute stages before renal dilatation is apparent: beware—the finding of a non-dilated PCS on ultrasound does not exclude obstruction in any patient with symptoms of renal colic. Spectral Doppler is useful in diagnosing acute, early renal obstruction, before PCS dilatation develops, because of the associated increase in blood flow resistance in the affected kidney (Fig. 7.14). This causes an increase in the resistance and pulsatility indices (RI and PI) on the obstructed side, due to a reduction in diastolic flow. A raised RI in itself is a non-specific finding, not necessarily indicating obstruction; it is known to be age-related or can be associated with extrinsic compression of the kidney (for example by a fluid collection or mass) or with some chronic renal diseases or vascular disorders.
This can be overcome by analysing Doppler spectra from both kidneys and evaluating any difference between the two sides. A marked difference in the RI between the kidneys in a patient with renal colic points towards obstruction of the kidney with the higher resistance. A difference in RI of greater than 6 is highly suspicious of obstruction in a patient with renal colic; a reduction in the RI on the affected side can be observed when the obstruction has been relieved or after the renal PCS has become dilated. This effect often does not persist once the kidney dilates, presumably because the intrarenal pressure is relieved, which emphasizes the use of Doppler in acute cases, before dilatation has become established.14 Because of the vagaries of the stage of obstruction, renal pressure, etc. the interpretation of RI should be made cautiously. IVU will show delayed PCS opacification and is also more useful than ultrasound in assessing the level of obstruction. CT IVU, as mentioned previously, is more commonly fulfilling the role previously held by the IVU.
ultrasound images A patient with acute renal colic has a normal-looking, non-dilated RK with a raised resistance index of 75.8. IVU subsequently confirmed early obstruction of the RK. The resistance index (RI) subsequently returned to normal following relief of the obstruction.
ultrasound images In the same patient, the contralateral, normal kidney has a much lower resistance index of 67.2%.
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