BACKGROUND: Left-sided acute appendicitis, although well described in the literature, is still an easily missed diagnosis. Midgut malrotation and situs inversus are 2 known leading conditions that contribute to misdiagnosis of appendicitis.

CASE REPORT: Here is the case of a 27-year-old male without any previous medical history, who presented with left lower quadrant tenderness and was misdiagnosed with gastroenteritis as an outpatient and sent home; the patient presented the next day to the emergency department where he was found to have acute appendicitis with situs inversus. He underwent laparoscopic appendectomy where a phlegmon was identified. Pathology came back as peri-appendiceal mucocele with no signs of malignancy.

CONCLUSIONS: This case report aimed to revisit the idea of left-sided acute appendicitis and discuss the management of a perforated appendiceal mucocele contained by a phlegmon.

Keywords: Abdominal Pain, Appendectomy, appendicitis, Diagnostic Errors, Gastroenteritis, Mucocele, Situs Inversus