ObjectiveTo analyze the multidetector computed tomography (MDCT) findings of normal appendices and appendices of acute appendicitis in old patients, and to explore the clinical value of MDCT in assessing acute appendicitis in old patients. MethodsSixty-six cases of acute appendicitis confirmed by surgery in 24 hours after MDCT scan from Jun. to Oct. 2016 (acute appendicitis group), and 40 cases underwent MDCT scan for non-abdominal pain causes without appendiceal lesions from Sep. to Oct. 2016 (normal appendices group), were included, and the MDCT images of both 2 groups were retrospectively analyzed. Observation items included:location, diameter, mural thickness, intra-luminal contents, and changes of surrounding structures. Results① Rate of appendices visualization. In total of 95.5% (63/66) appendices were visualized on MDCT in acute appendicitis group, while 95.0% (38/40) appendices were visualized on MDCT in normal appendices group (P > 0.05). ② Locations of appendices. Acute appendicitis group:appendices were found to be located at pelvic cavity in 22 cases, in front of ileum in 2 cases, behind ileum in 10 cases, below cecum in 25 cases, and behind cecum in 4 cases. Normal appendices group:appendices were found to be located at pelvic cavity in 15 cases, in front of ileum in 3 cases, behind ileum in 7 cases, below cecum in 5 cases, and behind cecum in 8 cases. There was significant difference between 2 groups in terms of location of appendices (P < 0.05). The appendices in acute appendicitis group located mainly at pelvic cavity and below cecum, while the appendices in normal appendices group located mainly at pelvic cavity. ③ The diameter and thickness of appendices. The appendiceal diameter and thickness in acute appendicitis group were (11.4±4.2) mm (6.2-21.9) mm and (4.3±2.2) mm (1.1-8.6) mm, respectively, while those in normal appendices group were (6.1±1.4) mm (3.7-8.6) mm and (1.7±0.8) mm (0.5-3.2) mm, respectively. The diameter and thickness of appendices in acute appendicitis group were significantly greater than those in normal appendices group, respectively (P < 0.05). ④ Contents of appendices. Acute appendices group:there was effusion with air in 14 cases in appendiceal cavity, full of effusion in 36 cases, and appendicolith combined with effusion in 13 cases. Normal appendices group:there was full of air in 15 cases in appendiceal cavity, air with a little faeces of higher density in 13 cases, and nothing in 10 cases. Effusion was more common in appendiceal cavity in acute appendicitis group, while air was more common in normal appendices group. ⑤ Around appendices. Fat stranding was seen in 57 cases, adjacent parietal peritoneum thickening was seen in 56 cases, focal effusion was seen in 18 cases, abscess was seen in 2 cases, free air in peritoneal cavity was seen in 8 cases, and lymphadenopathy was seen in 35 cases. None of these imaging features were seen in normal appendices group. ConclusionsMDCT can demonstrate features of normal appendices and acute appendicitis in old patients. MDCT yield high diagnostic accuracy in acute appendicitis in old patients, and can provide useful information before surgery.