IMPORTANCE: The role of interval appendectomy after conservative management of perforated appendicitis remains controversial. Determining the etiology of perforated appendicitis is one reason to perform interval appendectomies.

OBJECTIVE: To determine whether adult patients undergoing interval appendectomy experience an increased rate of neoplasms.

DESIGN: Retrospective study.

SETTING: A single tertiary care institution.

PARTICIPANTS: All patients 18 years or older who underwent appendectomy for presumed appendicitis from January 1, 2006, through December 31, 2010.

EXPOSURES Appendectomy for presumed appendicitis.

MAIN OUTCOMES AND MEASURES: Underlying neoplasm as the cause of presentation for presumed appendicitis. Demographic data, clinicopathologic characteristics, interval resection rate, and complication data were collected and analyzed.

RESULTS: During the study period, 376 patients underwent appendectomies. Interval appendectomy was performed in 17 patients (4.5%). Neoplasms were identified in 14 patients (3.7%); 5 of those tumors occurred in patients who had undergone interval appendectomy (29.4%). Nine neoplasms were mucinous tumors (64.3%), including all neoplasms associated with interval appendectomies. The mean age of all patients with appendiceal tumors was 49 years (range, 35-74 years).

CONCLUSIONS AND RELEVANCE: Mucinous neoplasms of the appendix were found in 5 of 17 patients (29.4%) undergoing interval appendectomy. Interval appendectomies should be considered in all adult patients, especially those 40 years or older, to determine the underlying cause of appendicitis. A multi-institutional study to determine the generalizability of these findings is warranted.