Carpenter’s Level Sign

One of the most important things a radiologist must do when interpreting a barium enema is to distinguish polyps from air bubbles and other filling defects. This applies to both solid-column and double-column barium enemas. John Mulloy and Randall Scott ¹ (University of Tennessee, Memphis) have aided us in this task with regard to the solidcolumn barium enema, by their recent description of the ‘carpenter’s level sign’ ¹ . When a filling defect maintains a central position on a solid-column barium enema, with views at 90° (e.g. supine and lateral), a carpenter’s level air bubble sign is present (Figure 1). As in a carpenter’s level (Figure 2), the filling defect in the column is an air bubble seeking the highest point in the column. After discussing the movement of an air bubble verses a polyp, during a film interpreting session, the authors devised a model that would simulate the in vivo findings (Mulloy, personal communication). ‘An air bubble and a sessile polyp can occupy similar positions within the image of the colon [on supine or prone films] if the polyp is located centrally on the anterior or posterior wall. When the model was turned 90°, the air bubble was seen to hold its central position in the highest point of the column, whereas the polyp moved with the direction of rotation to display a profile view from what was then the lateral wall.’ ¹ The authors then confirmed their experimental results during barium enema examination of patients. Figure 1 ‘Comparison of radiographic appearance of an air bubble and a sessile polyp in perpendicular views. A, an air bubble (arrow) and a sessile polyp (a gumdrop in this model; arrowhead) can produce a nearly identical appearance on radiographs. B, after model is rotated 90 degrees, simulated polyp (arrowhead) is seen in profile projecting from lateral wall. Air bubble (arrow) has maintained central highest point—a positive ‘carpenter’s level sign’.’ Reprinted from Mulloy and Scott’. Differentiating colonic polyps from air bubbles on barium enema: the ‘carpenter’s level sign’. <italic>Am. J. Roentgenol.,</italic> <bold>1994, 163, 84</bold>–6, with the permission of the ARRS https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003076568/34c29fd5-5662-4e8f-b58c-badd7fa5d724/content/fig13_1_B.jpg"/> Figure 2 A carpenter’s level https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003076568/34c29fd5-5662-4e8f-b58c-badd7fa5d724/content/fig13_2_B.jpg"/>