Appendiceal mucinous neoplasms are rare lesions of the appendix, with about 1500 new cases reported annually in the United States. They most commonly present in patients in their 50s and 60s, with a slightly higher incidence in females. They often present asymptomatically and are discovered incidentally on imaging or colonoscopy. If symptomatic, signs can include abdominal pain, abdominal tenderness, palpable mass, constipation, nausea, vomiting, and weight loss. Abdominal CT may reveal a soft-tissue mass in the right lower quadrant (RLQ), with mural curvilinear calcification. Other signs can include intussusception, appendicitis, appendicular abscess, or obstruction.

The clinical course of appendiceal mucinous neoplasms has a wide range that depends on the specific diagnosis, stage, and histologic grade of the neoplasm. Appendiceal mucinous neoplasms include serrated polyps, hyperplastic polyps, low-grade appendiceal mucinous neoplasms (LAMNs), high-grade appendiceal mucinous neoplasms (HAMNs), and mucinous adenocarcinomas of the appendix. Low-grade tumors confined to the appendix can be slowly progressing with good prognosis, whereas high-grade adenocarcinomas can be aggressive with high rates of reoccurrence.

Prognosis also depends on whether there is progression to pseudomyxoma peritonei, characterized by peritoneal spread of mucin. As the appendiceal mucinous neoplasm proliferates, mucin accumulates and can involve the peritoneal cavity in cases of mucin dissecting through the wall, or mural perforation. Complication by pseudomyxoma peritonei indicates advanced-stage disease, and prognosis is less favorable. Around 20% of patients with an appendiceal mucinous neoplasm develop pseudomyxoma peritonei.