Rationale: The horseshoe anomaly of the vermiform appendix is extremely rare. Preoperative confirmation of this anomaly is difficult; therefore, routine procedures, such as appendectomy, may become unexpectedly challenging when such anomalies are encountered during the surgical process.
Patient concerns: A 33-year-old man presented with abdominal pain in the right lower abdomen owing to acute appendicitis confirmed via computed tomography. Immediate laparoscopic appendectomy was decided as the method for treatment.
Diagnosis: Horseshoe anomaly was diagnosed as a gross finding during surgery.
Intervention: First, the appendiceal base was resected and appendectomy was performed via the retrograde method because the appendiceal tip was curled behind the cecum. However, it was discovered that the appendiceal tip was connected to the lateral part of the ascending colon and showed a horseshoe-shaped anomaly. The second appendiceal base arising from the ascending colon was also ligated, and the appendectomy was completed without any further complications.
Outcomes: After successful completion of appendectomy, the patient was discharged without any complications 2 days later.
Lessons: An appendiceal anomaly is rarely seen during appendectomy or other forms of abdominal surgery; however, the ability of surgeons to both recognize and categorize an appendiceal anomaly is crucial if detected during surgery. After successfully recognizing the horseshoe anomaly of the appendix, it is important to know that 2 appendiceal base ligations will be required to complete the surgery successfully.