Is ultrasound (US) or kidney, ureter, and bladder (KUB) X-ray better for evaluating costovertebral angle (CVA) tenderness?

From the Guidelines

Neither ultrasound nor KUB X-ray is specifically indicated for evaluating costovertebral angle tenderness, as CVA tenderness is a clinical finding assessed through physical examination, not through imaging. When a healthcare provider checks for CVA tenderness, they tap or punch the area over the kidneys (the costovertebral angle) to elicit pain, which may indicate kidney inflammation or infection. Once CVA tenderness is identified clinically, imaging studies like ultrasound or CT scan may be ordered to evaluate the underlying cause, such as pyelonephritis, kidney stones, or other renal pathology.

Key Points to Consider

• Ultrasound is generally preferred as the initial imaging modality for suspected kidney issues because it avoids radiation exposure, provides real-time images, and can detect hydronephrosis, stones, and other abnormalities 1.
• KUB X-ray has limited sensitivity for many kidney conditions but may be useful for visualizing larger kidney stones 1.
• The choice between imaging modalities should be based on the suspected diagnosis after clinical assessment of CVA tenderness, not for evaluating the tenderness itself.
• Recent studies suggest that combining US findings with complementary KUB improved the sensitivity for urolithiasis and had acceptable specificity when compared with either modality alone 1.

Recommendations

• Ultrasound is the preferred initial imaging modality for evaluating suspected kidney issues due to its ability to avoid radiation exposure and provide real-time images 1.
• KUB X-ray may be considered as an adjunct to ultrasound in certain cases, such as visualizing larger kidney stones 1.
• The most recent and highest quality study supports the use of ultrasound as the initial imaging modality for suspected kidney issues 1.

From the Research

Evaluating CVA Tenderness

• For evaluating costovertebral angle (CVA) tenderness, the choice between ultrasound (US) and kidney, ureter, and bladder (KUB) X-ray depends on various factors, including the clinical presentation and the suspected underlying condition 2, 3.
• Ultrasound has been shown to be useful in confirming or refuting suspected cases of acute pyelonephritis, particularly when used in conjunction with sonopalpation, which may aid in localizing pain to discrete anatomic structures 3.
• However, for the detection of ureteral stones, ultra-low-dose CT (ULD CT) has emerged as a highly sensitive and specific imaging modality, outperforming both US and KUB in certain cases, especially for small and distal ureteral stones 4.
• A study comparing the diagnostic accuracy of US and unenhanced CT for stone and obstruction in patients with renal failure found that US was sensitive and specific for renal stones (81% and 100%, respectively) but had lower sensitivity for ureteric stones (45%) 5.
• The combination of US and KUB has been suggested as a less invasive and more sensitive approach than intravenous urography for the diagnosis of calculi in patients with symptoms and signs suggestive of stone disease 6.

Comparison of Imaging Modalities

• US is preferred for its sensitivity in detecting renal stones and hydronephrosis, but its sensitivity for ureteric stones is lower 5.
• KUB X-ray is superior for the diagnosis of ureteral stones but may not detect all renal stones, especially smaller ones 6.
• The choice between US and KUB should be guided by the clinical context, including the patient's symptoms, laboratory findings, and the suspected location of the stone or obstruction 2, 3, 4.