Abstract
OBJECTIVES: To investigate the feasibility of relative CT numbers to periappendiceal fat attenuation as an applicable index for estimating the severity of acute appendicitis. METHODS: In total, 308 consecutive surgery-confirmed acute appendicitis patients and 243 controls with available preoperative CT were analyzed retrospectively. The radiological parameters were appendix diameter, length, and wall thickness as concurrent appendicitis signs. CT numbers of periappendiceal fat, mesenteric fat, subcutaneous fat in the anterior and posterior abdominal wall, retroperitoneal fat, gluteal subcutaneous fat and psoas major muscle were measured, as well as the relative CT numbers of periappendiceal fat compared with other locations. RESULTS: There were 287 suppurative acute appendicitis (SAA) and 21 gangrenous or perforated acute appendicitis (GPAA) cases confirmed by pathology. The CT number of periappendiceal fat was significantly higher in patients than in controls (P＜0.01) although there was a wide overlap (-72.33 HU-117.43 HU). Significant differences in relative CT numbers were observed between the groups in gluteal subcutaneous fat (R(CTgl)) and psoas major muscle (R(CTps)) (P＜0.01). The AUCs of R(CTgl) and R(CTps) showed high accuracy to discriminate acute appendicitis from controls (AUC = 0.803, 0.761; 0.854, 0.847) and GPAA from SAA (AUC = 0.905, 0.851). CONCLUSIONS: Attenuation of periappendiceal fat on CT is related to the severity of appendicitis, and relative CT numbers (R(CTgl) and R(CTps)) could be an applicable index for severity determination. ADVANCES IN KNOWLEDGE: Periappendiceal fat infiltration is related to the severity of acute appendicitis (especially relative CT number). Other clinical and CT features also need to be considered in the evaluation of inflammation.