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Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

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1. In a retrospective review of 72 patients with renal stones that underwent unenhanced computed tomography (CT) followed by contrast-enhance CT in the portal venous phase, the overall sensitivity of contrast-enhanced CT for stones greater than 2mm in size was 99%.

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Evidence Rating Level: 3 (Average)

Study Rundown:

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Renal stone disease is common in emergency and primary care settings associated with renal colic and hematuria. A non-contrast enhanced CT is the preferred imaging modality of choice for detection of renal stones given the strong contrast between stone and surrounding kidney parenchyma. However, symptoms of renal colic can be mimicked by other acute abdominal or urological diseases, which is better evaluated with a contrast-enhanced CT scan. The purpose of this retrospective review was to investigate the sensitivity of kidney stone detection in contrast-enhanced CT scans.

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The study retrospectively reviewed 72 patients with at least one renal stone that underwent both unenhanced CT scan followed by contrast-enhanced CT in the portal venous phase. Two expert evaluators independently recorded the number of stones seen in the contrast enhanced images. At the conclusion of the trial, the average sensitivity of the axial contrast-enhanced images for stones greater than 2 mm and 3 mm in size was 98.5% and 100%, respectively. The study is limited by the relatively small sample size as well as a lack of a true reference standard for renal stones aside from the non-contrast enhanced CT scan. However, the results of this study support the hypothesis that contrast-enhanced CT scans may have high sensitivity in detecting renal stones. This can be helpful in patients presenting with non-specific symptoms, where the pre-test probability of a non-stone related etiology is high.

In-Depth [retrospective cohort]:

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This was a retrospective cohort study of 59 patients with a diagnosis of renal stones that had both a non-contrast and contrast-enhanced CT scan in the portal venous phase between 2009 to 2014 in a single center in the United States. Exclusion criteria included patients with medullary nephrocalcinosis, polycystic kidney disease, or with significant CT motion artifact. CT scans were reconstructed at a thickness of 1.25mm with maximum projection intensity images. Image analysis on the contrast-enhanced CT scans was performed by two independent subspecialty radiologists blinded to the clinical information and radiology reports. The reference standard was the number and size of stones seen on the non-contrast enhanced CT scan. At the conclusion of the trial, the sensitivity of thin axial images was 89.9% (95%CI 83.5 to 94.0%), 99.0% (95%CI 94.0 to 99.9%), and 100.0% (95%CI 92.2 to 100.0%) for reviewer 1 and 83.1% (95%CI 75.9 to 88.6%), 98.0% (95%CI 92.6 to 99.7%) and 100.0% (95%CI 92.2 to 100.0%) for reviewer 2 for all stones, stones greater than 2mm, and stones greater than 3mm, respectively.

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