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Investigation of loin pain

Departments of ¹ Radiology and ² Urology, Derriford Hospital, Plymouth PL6 8DH, UK

• Evaluation of a patient presenting with acute loin pain is a common reason for emergency referral to a radiology department. In the majority of cases the prime diagnostic consideration will be colic due to a ureteric stone.
  
• Although most ureteric stones are sufficiently radio-opaque to be visible on a plain radiograph of the abdomen, they are frequently obscured by bony structures and bowel contents. Other abdominal calcifications, particularly phleboliths, can be impossible to differentiate from ureteric stones. For this reason a plain film alone is usually not adequate for diagnosis. IVU has been the traditional method of diagnosing ureteric calculi and although it has a high sensitivity in demonstrating ureteric obstruction it frequently cannot directly identify a stone as the cause. It also requires the use of intravenous contrast medium, exposes the patient to ionising radiation, and diagnosis may be delayed by the need for late films.
  
• Ureteric stones are usually difficult to identify with ultrasound, which instead relies on evidence of obstruction to indirectly indicate the presence of a stone. The presence of hydronephrosis lacks specificity in this regard but diagnostic accuracy may be improved by identifying changes in intrarenal blood flow that occur in acute obstruction and by the analysis of ureteric jets. In combination with a plain radiograph, ultrasound provides an acceptable imaging technique when CT is not available. The use of ultrasound is particularly attractive in patients presenting with loin pain in pregnancy in whom it should be the primary imaging investigation.
  
• Unenhanced spiral CT has now become the imaging technique of choice for most patients with flank pain, not only owing to its unrivalled ability to directly visualise ureteric stones, but also its speed and ease of use. It provides all the imaging information required for patient management. CT also has the major advantage of demonstrating many other possible causes of loin pain in patients that do not have ureteric stones. The radiation exposure of CT must always be considered, particularly in young patients and those with recurrent stone formation, and dose reduction techniques should be applied whenever possible.
  

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