Objective The purpose of this study was to investigate whether changes occurred in the clinical features of acute colonic diverticulitis (ACD) over a period of 10 years, to estimate the long-term probability of disease recurrence and to investigate whether it could be treated in an outpatient setting.

Methods Between January 1998 and January 2009, 488 ACD patients were diagnosed and treated in Saiseikai Central Hospital, Tokyo. The diagnoses were made by ultrasonography (US) and/or CT. We investigated the time-dependent changes in the characteristics of patients with ACD, and we used the Kaplan-Meier method to estimate the cumulative probability of recurrence, based on information from a questionnaire.

Results The percentage of patients who were diagnosed with left-sided ACD significantly increased over time in comparison to those with right-side disease (4% in 1998, 36% in 2009). Patients with left-sided ACD were significantly older and were diagnosed at a more advanced disease stage than those with right-sided ACD. Among the 212 ACD patients who responded to the questionnaire, the cumulative probability of recurrence in 125 patients with no history of ACD at 2.9, 5.9 and 10.1 years was 16.0%, 20.1% and 26.2%, respectively. The probability of recurrence in patients with right-sided and left-sided ACD did not differ to a statistically significant extent. In addition, outpatient treatability in patients with left-sided to right-sided ACD did not differ to a statistically significant extent (66.6% vs. 70.1%).

Conclusion The ratio of left-sided to right-sided ACD was found to have increased over the past decade. Left-sided ACD patients were older and their incidence of complications was higher in comparison to right-sided patients; however, the rate of recurrence and outpatient treatability in patients with left-sided and right-sided ACD did not differ to a statistically significant extent.