Left Side Appendicitis with Abscess Caused by Midgut Malrotation Mimicked by Complicated Diverticulitis of Sigmoid Colon: A Case Report.

Midgut malrotation (MM) is a rare anatomical abnormality that complicates the diagnosis and management of acute abdominal pain. Moreover, appendicitis and diverticulitis of the sigmoid colon can be considered when there is pain in the lower left abdomen. The patient in this case report was an 86-year-old female who had continuous abdominal pain two days before the visit to the emergency room. Abdominopelvic computed tomography revealed MM, and uneven concentric wall thickening from the distal descending colon to the proximal sigmoid colon with surrounding fatty infiltration was confirmed in the left lower abdomen. Moreover, the possibility of left-sided appendicitis due to MM could not be excluded. The patient's abdominal pain increased next day. The surgery was performed laparoscopically, and the location of the appendix was reversed. The surgical findings revealed an abscess caused by perforation from inflammation of the proximal part of the appendix, and the sigmoid colon adhered mildly to the side immediately behind the abscess cavity. The base of the appendix was intact, and only an appendectomy was performed. Left-sided appendicitis due to MM was discriminated from the diverticulitis of the sigmoid colon. Diagnostic laparoscopic surgery through a physical examination based on the surgeon's experience is important.