A Case of Appendiceal Mucocele due to Low-grade Appendiceal Mucinous Neoplasm Correctly Differentiated from Acute Appendicitis Based on Diffusion-weighted Imaging and the Apparent Diffusion Coefficient Value

• Published in: Japanese Journal of Magnetic Resonance in Medicine Vol. 40; no. 1; pp. 14 - 19
• Main Authors: INOUE, Akitoshi, YOSHIDA, Erina, OTSUKI, Akinori, OHTA, Hiroyuki, MEKATA, Eiji, TSUJIKAWA, Tomoyuki, WATANABE, Shobu, OTA, Shinichi, NITTA, Norihisa, MURATA, Kiyoshi
• Format: Journal Article
• Language: English
• Published: Japanese Society for Magnetic Resonance in Medicine 15.02.2020
• Subjects: acute appendicitis; apparent diffusion coefficient value; appendiceal mucocele; diffusion-weighted image; low grade appendiceal mucinous neoplasm
• ISSN: 0914-9457; 2434-0499
• DOI: 10.2463/jjmrm.2019-1688

Patients with inflammation- or perforation-induced appendiceal mucocele may present with right lower abdominal pain, and a dilated appendix, resembling acute appendicitis, is demonstrated on imaging examination. Ruptured appendiceal mucocele due to appendiceal mucinous neoplasm may result in peritoneal dissemination and pseudomyxoma peritonei. Therefore, it is occasionally challenging but essential to distinguish appendiceal mucocele from acute appendicitis. A 65-year-old man presented with right lower abdominal pain. Computed tomography showed a dilated appendix without wall thickening, atypical of acute appendicitis. Magnetic resonance imaging (MRI) demonstrated high signal intensity on T2-weighted imaging and low signal intensity on diffusion-weighted imaging (DWI) of the dilated appendiceal component. The appendiceal component had an apparent diffusion coefficient (ADC) value of 3.351×10−3 mm2/s. Based on the MRI findings, appendiceal mucocele due to appendiceal mucinous neoplasm, particularly low-grade appendiceal mucinous neoplasm (LAMN) was more likely than acute appendicitis. Laparoscopic right hemicolectomy with lymph node dissection was performed instead of routine appendectomy 17 days after the MRI examination. Histopathology revealed LAMN with a small perforation. The postoperative course was uneventful, and she discharged without complications. No recurrences were observed 1 year after the operation. The dilated appendix with thin wall showing high signal intensity on DWI, and the appendiceal component without significant diffusion restriction could be characteristic findings of appendiceal mucocele due to LAMN and helpful in distinguish them from acute appendicitis. Herein, we report this case with a literature review focused on the utility of MRI including DWI and ADC value in acute abdominal pain.