Acute flank pain is the most common urological presentation in the emergency room. The diagnostic workup requires comprehensive history-taking, physical examination and radiological investigation. Although the present day urologist's armamentarium is replete with investigative tools, the ideal initial radiological workup remains controversial .
Urinary tract imaging is required prior to ESWL to identify the cause and degree of obstruction. Obstruction most commonly is due to stones, but may have many other aetiologies. Urinary tract imaging can also determine the site and size of the stone and delineate the intracalyceal anatomy. Intravenous urogram has been the standard imaging modality in uroradiology since the 1930s . It is able to demonstrate the anatomy of the entire urinary tract, it localizes the site and level of obstruction, and provides a gross assessment of excretory renal function. Some of its potential drawbacks, however, are its associated contrast reaction, inability to identify radiolucent calculi, contraindications to use in renal failure and, often it takes long time for acquiring delayed films in cases of obstruction.
In recent years, UHCT has proved to be an accurate radiographic modality . The potential benefit of UHCT is its use in patients with contrast allergies, pre-existing renal failure and unclear clinical diagnosis mimicking renal colic. Unenhanced helical CT has proven to be an accurate, safe and rapid examination for diagnosing and treating patients presenting with acute flank pain. Helical CT can be used in place of IVU to plan treatment of patients with flank pain caused by obstructing ureteral stones. Stones that are larger than 5 mm, located within the proximal two-thirds of the ureter and seen on two or more consecutive CT images are more likely to require endoscopic removal, lithotripsy, or both. Computed tomography is adequate for both diagnosis and treatment. Besides stone visualization, UHCT detects obstructions by several indirect signs, such as pyelo-ureteral dilatation, perinephric and periureteral stranding, renal enlargement, renal sinus fat blurring and rim sign [11–13], which are useful when a stone is not readily identifiable. The superiority of UHCT compared with IVU in terms of sensitivity and specificity has been confirmed in a number of recent clinical trials [4–6].
Identification of concomitant anatomical abnormalities and coexisting urinary (acute pyelonephritis, subcapsular renal haematoma) and non-urinary abnormalities is important for making therapeutic decisions . Using a functional study (IVU, magnetic resonance, CT urography and radioisotope studies) ensures that UPJ obstruction cannot be missed. Non-calculus ureteric obstruction can be identified on UHCT by indirect signs such as ureteric dilatation and peri-ureteric stranding, and on US by hydroureter. The findings of this study indicate that, in a selected group of patients, contrast study prior to treating ≤ 20 mm renal and ureteric stones by ESWL is not necessary.