Complicated and uncomplicated appendicitis follow different epidemiological trends also suggesting different pathophysiology behind these two different forms of appendicitis. In 3-10% of patients complicated acute appendicitis is enclosed by formation of a circumscribed periappendicular abscess. The clinically established practice of antibiotic therapy and drainage, if necessary, has been shown safe and effective, allowing the acute inflammatory process to subside in more than 90% of cases without surgery. The need of subsequent interval appendectomy has been questioned with appendicitis recurrence risk varying between 5-26%.

During trial enrollment in our randomized Peri-APPAC trial based on the interim analysis results with 17% appendiceal tumor rate in the study population, the trial was prematurely terminated based on ethical concerns. All the follow-up group patients were re-evaluated and surgery was offered and recommended to all follow-up group patients. After this assessment and additional appendectomies, two more tumors were diagnosed resulting in neoplasm rate of 20% in the whole study group all diagnosed in patients over 40 years and the neoplasm rate in patients over 40 years was 29%.

Based on high appendiceal tumor rate in patients over 40 years, the appendiceal neoplasm rate needs to be further evaluated in prospective patient cohorts undergoing interval appendectomy as interval appendectomy is generally well tolerated and obliterates the risk of missing a possible tumor. In a recent systematic review of retrospective cohort studies with 13.244 acute appendicitis patients the overall appendiceal tumor rate was 1% after appendectomy, but in patients presenting with appendiceal inflammatory mass the neoplasm rate varied from 10% to 29%.

This nationwide prospective multicenter cohort study is designed to assess the prevalence of appendiceal tumors associated with a periappendicular abscess. All consecutive patients presenting with a periappendicular abscess are recommended to undergo interval appendectomy after initial conservative treatment with antibiotic therapy and drainage, if necessary. All patients older than 35 years will undergo laparoscopic interval appendectomy at 2 to 3 months and this is also recommended for the patients between 18 and 35 years of age. Asymptomatic patients under 35 years not willing to undergo interval appendectomy, will undergo a follow-up MRI at 1 year after the initial non-operative treatment.

Complicated and uncomplicated appendicitis follow different epidemiological trends also suggesting different pathophysiology behind these two different forms of appendicitis. In 3-10% of patients complicated acute appendicitis is enclosed by formation of a circumscribed periappendicular abscess. The clinically established practice of antibiotic therapy and drainage, if necessary, has been shown safe and effective, allowing the acute inflammatory process to subside in more than 90% of cases without surgery. The need of subsequent interval appendectomy has been questioned with appendicitis recurrence risk varying between 5-26%.

During trial enrollment in our randomized Peri-APPAC trial, the high incidence of appendiceal tumors in the study population alarmed the researchers. Based on the interim analysis results with 17% appendiceal tumor rate in the study population, the trial was prematurely terminated based on ethical concerns. All the follow-up group patients were re-evaluated and surgery was offered and recommended to all follow-up group patients. After this assessment and additional appendectomies, two more tumors were diagnosed resulting in neoplasm rate of 20% in the whole study group all diagnosed in patients over 40 years and the neoplasm rate in patients over 40 years was 29%.

Based on high appendiceal tumor rate in patients over 40 years, the appendiceal neoplasm rate needs to be further evaluated in prospective patient cohorts undergoing interval appendectomy as interval appendectomy is generally well tolerated and obliterates the risk of missing a possible tumor. In a recent systematic review of retrospective cohort studies with 13.244 acute appendicitis patients the overall appendiceal tumor rate was 1% after appendectomy, but in patients presenting with appendiceal inflammatory mass the neoplasm rate varied from 10% to 29%.

This nationwide prospective multicenter cohort study is designed to assess the prevalence of appendiceal tumors associated with a periappendicular abscess. All of the study hospitals will have a common clinical protocol of recommending interval appendectomy to all patients presenting with a periappendicular abscess after initial conservative treatment with antibiotic therapy and drainage, if necessary. Considering the high rate of appendiceal neoplasms, all patients older than 35 years will undergo laparoscopic interval appendectomy at 2 to 3 months after the successful initial non-operative treatment and this is also recommended for the patients between 18 and 35 years of age. Asymptomatic patients under 35 years not willing to undergo interval appendectomy, will undergo a follow-up MRI at 1 year after the initial non-operative treatment.

Inclusion Criteria:

• periappendiceal abscess proven by CT, Mri or US

Exclusion Criteria:

• patient declines to participate, complicated appendicitis without periappendiceal abscess

IPD is available from the PI upon request, if needed.

At study completion

Please see above.