Appendiceal mucus cyst is a kind of retention cyst, not a real tumor, and is relatively rare in clinical practice. The etiology of appendiceal mucus cyst is still unclear, mostly secondary to appendiceal inflammation, because the appendiceal cavity is occluded by fecal stones and the mucosal secretions cannot be discharged normally, and the appendix gradually expands to form a gelatinous mucus cyst. It is classified as: 1) simple mucous cyst; 2) appendiceal pseudomucinous tumor; 3) mucous cyst adenoma; 4) mucous cyst adenocarcinoma, and some scholars support that appendiceal mucous cyst is a new tumor of the appendix. The pathophysiology of appendiceal mucinous tumor: Appendiceal mucinous cyst is mainly caused by appendiceal inflammation causing narrowing or obstruction in the appendiceal lumen, and the mucus secreted by mucus cells in the mucosal epithelial tissue of the distal appendix cannot be discharged, and the appendiceal lumen expands to form a cyst due to mucus retention, which is actually a retention cyst. Mucinous cystadenoma is characterized by atypical glandular infiltration in the appendiceal wall and crossing the mucosal muscle layer, or by peritoneal implantation to form a peritoneal pseudomucinous tumor without hematologic or lymphatic metastasis, and is therefore considered by most scholars to be a junctional or low-grade malignant tumor.