Asymptomatic Appendiceal Mucocele with Typical Onion Skin Sign on Ultrasound

Abstract

Appendiceal mucocele is an obstructive dilatation of the appendix caused by abnormal accumulation of mucoid material. Its incidence is 0.2-0.3% of all appendectomy specimens and it does not have typical clinical features. It can mimic acute appendicitis in patients with right lower quadrant pain. Some patients have appendiceal mucocele with acute appendicitis. For this condition, 25% of cases were asymptomatic and were discovered incidentally on ultrasound examination, computed tomography, or colonoscopy due to nonspecific abdominal symptoms. Ultrasound examination or computed tomography is an important diagnostic tool for accurate preoperative diagnosis. If mucocele is treated incorrectly, pseudomyxoma peritonei may develop. The present study reports a case of a 79-year-old male with constipation. Ultrasonography showed a typical layered echogenic pattern of the appendiceal wall (onion sign or onion skin sign), which suggested appendiceal mucocele. Computed tomography showed a dilated appendix filled with low-attenuated material, indicating a pathologic diagnosis of low-grade appendiceal mucinous neoplasm.