Radiological Diagnosis of "Renal Colic"

The IVU has been the traditional imaging method for the diagnosis of acute ureteric obstruction. It has now been replaced with multislice CTof the urinary tract  with low-dose technique  (CT Urogram or CTU) .

CTU has established advantages when compared to IVU:

Greater Accuracy - Sensitivity 97% and Specificity 96%. With CT all stones are visible as compared to traditional X - ray KUB and IVU where up to 20%, usually uric acid stones, are non-opaque.

Faster - when ureteric obstruction is present an IVU may take several-hours, while a CTU in the same situation requires only 15-30 minutes.

Avoids IV Contrast Medium

Alternative Diagnoses - in reported series approximately 50% of those clinically suspected of "renal colic' are confirmed with imaging. In the remaining 50% who do not have renal colic, approximately 20% will have a CT demonstrated cause for their pain. This includes appendicitis, diverticulitis, gynaecological causes, carcinoma of the colon and ruptured aortic aneurysm.

Radiological Diagnosis

Primary Sign (Fig 1) Identification of a stone within the kidney, ureter or bladder. Virtually all stones greater than 2mm diameter will be visible. Pelvic phleboliths can be confusing.

Secondary Signs (Fig 1) These are due to increased pressure proximal to the stone and include enlargement of the kidney, perinephric fluid and dilatation of the pelvicalyceal system and ureter

Theoretical Disadvantages of CTU compared to IVU

Radiation Dosage -research at Christchurch Hospital showed that the total radiation dose from CTU is 1.4 times greater than for an IVU. This is an acceptable difference given the other advantages of CTU.

Dr Tony Young

CHRISTCHURCH RADIOLOGY GROUP