Differentiation of Periappendiceal Abscess from Acute Appendicitis by Semi-Quantitative Tc-HMPAO Labeled Leukocyte Scan

Received 9/2/2002; revised 11/23/2002; accepted 12/12/2002. For correspondence or reprints contact: Shung-Shung Sun, M.D., Department of Nuclear Medicine, China Medical College Hospital, 2 Yuh-Der Road, Taichung 404, Taiwan. Tel: (886)4-22052121 ext. 3475, Fax: (886)4-22023442, E-mail: [email protected] Background: Clinical management of periappendiceal abscess (ABS) and acute appendicitis (APP) is quite different. The latter needs early appendectomy while the former requires conservative treatment followed by elective interval appendectomy. The purpose of this study is to assess the reliability of Tc-HMPAO leukocyte scan (TC-WBC) with semi-quantitative method to differentiate ABS from APP. Methods: Twenty-five patients were referred due to atypical symptoms and signs of APP (M:F = 20:5, mean age = 44 y/o). The leukocyte was labeled with the method of Kao et al. [1]. The mean labeling efficiency is 75±9% (56-88%). At 4 h after injection, 800K counts static image over anterior abdomen was obtained. All patients were asked to void before imaging. Two ROIs were defined, one over the lumbar spine bone marrow (BM) and the other over the appendiceal zone (AZ). The mean pixel count of AZ/BM ratio (ABR) was calculated. Results: Six patients were diagnosed with APP and 9 patients with ABS by excisional biopsy. Ten patients with acute abdomen but with no appendicitis served as controls (CON). The mean ABR for CON, APP and ABS was 0.7503±0.0826, 0.8444±0.0930, and 1.1487±0.2142, respectively. The Rank test showed the ABR for ABS was significantly different from APP and CON (P < 0.05 and P < 0.001). With cutoff value of ABR ≥1.0000 defined as sensitivity, specificity, accuracy, positive predictive value and negative predictive value for TC-WBC to diagnose ABS were 78%, 100, 100, 89% and 92%, respectively. Conclusion: The semi-quantitative TC-WBC can effectively differentiate ABS from APP. This will provide the clinicians with useful tool in the diagnosis and management of the patients with ABS and APP.