High-grade appendiceal mucinous neoplasm presenting as a giant appendiceal mucocele.

Appendiceal mucinous neoplasms are rare findings defined by an accumulation of mucus within the vermiform appendix, and can be caused by a variety of conditions. Appendiceal mucinous neoplasms are important to consider because they can develop into pseudomyxoma peritonei as a consequence of perforation. We report a case of a 55-year-old man who initially presented with increasing abdominal girth, constipation, anorexia, and unintentional weight loss. Computed tomography examination of the abdomen and pelvis demonstrated a huge thin-walled cystic mass causing significant displacement of the surrounding abdominal and pelvic structures. The mass was amenable to resection and removed without perforation. Gross pathologic examination demonstrated a 44.0 × 40.0 × 23.0 cm unilocular cystic mass with a section of attached bowel. Microscopic examination revealed high-grade appendiceal mucinous neoplasm arising in a background of low-grade appendiceal mucinous neoplasm. This case report provides an evidence to include appendiceal mucinous neoplasms in the differential diagnosis of large abdominal cystic masses.