To retrospectively evaluate the multidetector computed tomography (MDCT) findings of extraperitoneal ascending appendicitis.

The MDCT examinations of 10 patients with extraperitoneal ascending appendicitis confirmed by laparoscopic surgery were retrospectively analyzed. Preoperative MDCT examinations were obtained after intravenous administration of iodinated contrast material in all patients. Transverse and coronal reformatted MDCT images were reviewed in consensus by two radiologists. The presence of the extraperitoneal triangle sign, the split interfascial plane sign, and the other classical findings of appendicitis were evaluated.

Luminal dilatation, wall enhancement of the inflamed appendix, and fat infiltration were present in 10/10 patients (100%). The perforation of the inflamed appendix with abscess formation was present in 4/10 patients (40%). The split interfascial plane sign was present in 7/10 patients (70%), and parts of inflamed appendix or periappendiceal abscess were located behind the right extraperitoneal triangle in 8/10 patients (80%).

The split interfascial plane sign and the presence of an appendiceal tip or periappendiceal abscess located in the right extraperitoneal triangle are highly suggestive of extraperitoneal ascending appendicitis on MDCT.