The CT at presentation was read as "probable sigmoid diverticulitis causing reactive appendicitis", with the caveat that the patient should be reimaged if he had persistent or worsening abdominal pain in order to ensure no appendiceal complication occurred. Primary acute appendicitis was felt unlikely due to the presence of oral contrast and air within the appendiceal lumen, and because the inflammation was centered the diverticulum. Appendiceal diverticulitis was felt unlikely because it is so rare. 

The patient returned one week later with diffuse abdominal pain. Follow-up CT images show definitively show that the inflamed diverticulum arose from the appendiceal tip, not the sigmoid colon. The inflammatory findings are now nearly resolved, with a small amount of remaining fluid/stranding. Nothing acute was found to account for his worsening pain. 

Appendiceal diverticulitis is a rare condition. The etiology and pathogenesis of acquired appendiceal diverticulosis are unknown. These patients are thought to have a higher risk of complications such as perforation and neoplasm ¹. Therefore, appendectomy is recommended in most cases.