Spontaneously resolving appendicitis: frequency and natural history in 60 patients.

PURPOSE: To establish the frequency and natural history of ultrasonographically (US) documented spontaneously resolving appendicitis following conservative treatment.

MATERIALS AND METHODS: From July 1987 to July 1997, the authors encountered 106 patients with US-diagnosed spontaneously resolving appendicitis. We retrospectively studied clinical data and US findings obtained at admission and follow-up relating to 60 patients who were treated conservatively. Over the same 10 years, 1,280 appendectomies for acute appendicitis were performed in the authors' hospital.

RESULTS: Of 60 patients, 23 (38%) had recurrent appendicitis after a median of 14 weeks (range, 2-254 weeks), with 16 (70%) having recurrence within 1 year of the first attack. US findings indicated that patients with an appendiceal diameter of at least 8 mm were more prone to recurrence than patients with an appendiceal diameter of less than 8 mm; the recurrence rates were 47% (21 of 45 patients) and 13% (two of 15 patients). The other parameters did not show a statistically significant difference.

CONCLUSION: Spontaneously resolving appendicitis occurs in at least one in 13 cases of appendicitis and has an overall recurrence rate of 38%, with the majority of cases reccurring within 1 year.