TUESDAY , DECEMBER 2 , 2003 Review Session for Residents : Generating a Meaningful Radiology

Large-colon torsion is a common cause of colic in horses and has a worse prognosis and highercost than other causes of surgical colic of the large colon. During large-colon torsion, the colonwall becomes thick due to vascular occlusion. Therefore, we hypothesized that detectingincreased colon-wall thickness during ultrasonography would be an accurate pre-operative testfor large-colon torsion. The sample population consisted of 42 horses that were admitted forsurgical treatment of colic localized to the large colon. The diagnosis was confirmed at surgeryor necropsy examination. Twelve (29%) of these horses were diagnosed with large-colon torsion.Duplicate ultrasonographic measurements of colon-wall thickness were made at 6 abdominallocations and an average measurement was calculated. For 4 of these 6 sites, a significantdifference (p<0.005) was detected between horses with and without large-colon torsion. All 4tests were highly specific and moderately sensitive for diagnosing large-colon torsion using 5decision criteria. Using a ventral abdominal window, a colon-wall thickness ≥ 9 mm accurately predicted large-colon torsion in 8/12 horses (sensitivity, 67%; confidence interval [CI], 36 to98%) and correctly predicted that large-colon torsion was absent in 28/28 horses (specificity,100%; CI 98 to 100%). Intraobserver repeatability was assessed by evaluating the differencebetween the first and second measurement obtained, which was ≤ 2 mm. Therefore, detectingincreased large-colon-wall thickness during ultrasonography is a reproducible and accurate pre-operative test for large-colon torsion in horses with surgical colic localized to the large colon.