Right-Sided Abdominal Pain in a Child With Situs Inversus and Left-Sided Acute Appendicitis: A Diagnostic Imaging Pitfall

Background: Situs inversus is a rare congenital anomaly characterized by mirror-image transposition of the viscera. Acute appendicitis in patients with situs inversus may be diagnostically challenging because the appendix is typically located on the left, while symptom localization may be atypical or discordant with the underlying anatomy. We present a pediatric case of left-sided acute appendicitis in a patient with known situs inversus who presented with predominantly right-sided abdominal pain.

Case Presentation: A 14-year-old boy presented to the pediatric emergency department with acute diffuse abdominal pain, more pronounced on the right, accompanied by nausea and vomiting. Because of clinical suspicion for acute appendicitis, he was referred for abdominal ultrasonography. Although the patient had known situs inversus, this information was not documented on the imaging referral. Initial graded-compression ultrasonography of the right lower quadrant did not visualize the appendix. During the examination, the spleen was unexpectedly identified on the right side, raising suspicion of reversed visceral anatomy. Review of prior imaging confirmed situs inversus. Targeted examination of the left lower quadrant was subsequently performed; however, the appendix remained nonvisualized.

Imaging Findings and Management: Because clinical suspicion persisted after nondiagnostic ultrasonography, contrast-enhanced CT was performed. CT confirmed situs inversus and demonstrated a left-sided appendix dilated to approximately 12 mm, with mural thickening and surrounding inflammatory fat stranding, consistent with acute appendicitis. The patient subsequently underwent laparoscopic appendectomy, with a postoperative diagnosis of acute phlegmonous appendicitis.

Conclusion: Acute appendicitis in situs inversus may present with symptoms that do not mirror the anatomical location of the appendix. This case highlights the importance of recognizing unexpected visceral orientation during ultrasonography, reviewing prior imaging, communicating known anatomical variants on imaging referrals, and proceeding to appropriate cross-sectional imaging when clinical suspicion persists after nondiagnostic ultrasonography.