Imaging test characteristics: Is sonography enough?
Thus, it is imperative that any pregnant patient that comes in to the hospital or clinic with abdominal pain be evaluated for appendicitis. Ultrasound was a valuable diagnostic tool in this case and saved both the patient and developing fetus the radiation exposure of a CT scan. Ultrasound has a high specificity for diagnosing appendicitis if the appendix is visualized with abnormal findings. However, the sensitivity is not as high as CT, and failure to visualize the appendix adequately would have required a decision between appendectomy on clinical grounds only or going through with the CT scan.
The sensitivity, specificity, and positive and negative predictive values for ultrasonography and CT scans in the diagnosis of appendicitis are given in the TABLE (level of evidence [LOE]=1a).7
In a prospective study of patients with clinical signs and symptoms of acute appendicitis using a graded compression technique of ultrasonography, sonographic testing was as accurate as the focused unenhanced single-detector helical CT. The primary sonographic criterion for diagnosing acute appendicitis was an incompressible appendix with a transverse outer diameter of 6 mm or larger, as seen in this patient. The sensitivity of CT and sonography was 76% and 79%, respectively; the specificity was 83% and 78%; the accuracy was 78% and 78%; the positive predictive value was 90% and 87%; and the negative predictive value was 64% and 65% (LOE=2a).8
In conclusion, it is reasonable to use graded compression ultrasonography in a pregnant woman with suspected appendicitis. If the suspicion for appendicitis is high, a negative result may still need further evaluation with a CT or ultimately lead to abdominal surgery despite negative imaging studies.
TABLEUltrasound and CT in the diagnosis of appendicitis
| TEST | SN | SP | LR+ | LR– |
|---|---|---|---|---|
| Ultrasound | 0.86 (0.83–0.88) | 0.81 (0.78–0.84) | 5.8 (3.5–9.5) | .019 (0.13–0.27) |
| CT | 0.94 (0.91–0.95) | 0.95 (0.93–0.96) | 13.3 (9.9–17.9) | 0.09 (0.07–0.12) |
| Sn, sensitivity; Sp, specificity; LR+, positive likelihood ratio; LR–, negative likelihood ratio; CT, computed tomography. | ||||
| Source: Teresawa et al, Ann Intern Med 2004.7 | ||||
Corresponding Author
Richard P. Usatine, MD, University of Texas Health Science Center at San Antonio, Department of Family and Community Medicine, MC 7794, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900. E-mail: usatine@uthscsa.edu