Prospective Double-Blinded Study of Abdominal-Pelvic Computed Tomography Guided by the Region of Tenderness: Estimation of Detection of Acute Pathology and Radiation Exposure Reduction

Study objective: Computed tomography (CT) is increasingly used for emergency department (ED) patients with abdominal tenderness. CT-related radiation contributes to 2% of US cancers. We hypothesized that in the ED patient with nontraumatic abdominal tenderness, the tender region accurately delineates acute pathology z axis-restricted CT guided by this region could detect pathology while reducing radiation dose. Methods: This was a prospective double-blinded observational trial with informed consent and was institutional review board-approved and registered with ClinicalTrials.gov. A convenience sample of ED patients undergoing abdominal CT was recruited, excluding pregnant women, patients with altered mental status or abdominal sensation, preverbal children, and patients with abdominal trauma or surgery in the previous month. Before standard CT, physicians demarcated the tender region with labels invisible to radiologists on abdominal windows. Radiologists blinded to the tender region recorded cephalad-caudad limits of pathology on CT. Personnel blinded to pathology location recorded label positions on lung windows. Two hypothetical CT strategies were then explored: CT restricted to the tender region and CT from the cephalad skin marker to the lower caudad limit of the usual CT The percentage of the pathologic region contained within the extent of the 2 hypothetical z axis restricted CTs was calculated. z axis reduction, which is linearly related to radiation reduction, from the restricted CTs was determined. Results: One hundred two subjects were enrolled, 93 with complete data for analysis. Fifty-one subjects had acute pathology on CT. CT limited to the tender region would reduce z axis (radiation exposure) by 69% (95% confidence interval [Cl] 60% to 78%). All acute pathology was included within these boundaries in 17 of the 51 abnormal cases (33%; 95% Cl 22% to 47%). CT from the cephalad marker through the caudad abdomen and pelvis would reduce z axis (radiation exposure) by 38% (95% Cl 29% to 48%). All acute pathology was included within these boundaries in 36 of 51 abnormal cases (71%; 95% Cl 57% to 81%). With both strategies 1 and 2, the pathologic region was at least partially included within the CT region in the majority of cases (84% and 92%, respectively) Conclusion: CT with z axis restriction based on abdominal tenderness could reduce radiation exposure but with a potentially unacceptably high rate of misdiagnosis, using our current methods. Further prospective study may be warranted to determine the diagnostic utility of partially visualized pathology. [Ann Emerg Med 2010;56.126-134.]