A previous report proposed ultrasonography-based classification as a promising means of predicting pediatric spontaneously resolving appendicitis. The present study investigated the long-term prognosis of supportive care for low-grade appendicitis identified by ultrasonography, defined as an appendix with a smooth submucosal layer irrespective of blood flow or an appendix with an irregular layer and increased blood flow.
The present, retrospective cohort study enrolled patients under 16 years of age with acute appendicitis at a children’s hospital between October 2010 and September 2016. The inclusion criteria were ultrasonography findings showing an appendix with (1) full visualization, (2) a diameter ≥6 mm, (3) a smooth submucosal layer or an irregular layer with increased blood flow, and (4) no appendiceal mass, abscess, or perforation. The exclusion criteria were: (1) a history of acute appendicitis, (2) antibiotic administration within 72 hours before diagnosis, and (3) antibiotic administration or surgery before supportive care. The primary outcome was the event-free duration, defined as a period of supportive care alone with no additional intervention or recurrence of appendicitis.
One hundred and eighty-two patients were enrolled. The median Alvarado score was 7 (interquartile range, 6-8), and the median follow-up duration in event-free cases was 1,922 days (interquartile range, 1,347-2,614 days). The event-free rate was 75.0%, 67.0%, and 62.5%, at 1, 2, and 5 years, respectively.
The long-term, event-free rate exceeded 60% in patients with low-grade appendicitis defined by ultrasonography who received neither surgery nor antibiotic treatment. Most recurrences occurred within 2 years of the initial diagnosis.

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