Intravenous urography (pyelography) is a designation for X-ray examination of the urinary tract. In many indications, it has been replaced by other imaging methods, but it still has a use in modern medicine.
The principle is in intravenous administration of the contrast agent. The word "contrast" means a solution that is visible on X-ray. The fluid flows through blood vessels and reaches kidneys, where it is filtered into the urine. Then, the contrast agent flows through the urinary tract towards the urinary bladder. The examiner can watch the flow of the contrast by taking repeated X-ray images. The contrast helps to visualize both kidneys, ureters and the urinary bladder.
The examination does not need any special preparation with the exception that it is performed on an empty stomach. The injected contrast agent can cause an allergic reaction and therefore, it is advisable to use an anti-allergic medication before the procedure.
The main importance of the intravenous urography is visualization of the urinary tract and detection of any narrowing or obstruction (cancers of the urinary tract, urinary stones, etc.). The examination can be performed in a patient with unilateral suspected hydronephrosis, when we want to find the reason of renal pelvis dilation and distinguish hereditary distended pelvis from its pressure distension due to obstruction of the urine flow.
In fact, the only problem is the risk of an allergic reaction after administration of the contrast agent. It is an exceptional case, but even strong allergy manifesting as anaphylactic shock can not be excluded. Preventive application of anti-allergic medication further minimizes the risk.
The main advantage of intravenous urography is its wide availability and non-invasiveness. The exposure to radiation is relatively low.