Appendiceal adenoma is a precancerous lesion of appendiceal adenocarcinoma: Appendiceal adenoma is defined as the absence of evidence of infiltration. A diagnosis of appendiceal adenoma implies a cure by total resection. If there is any doubt, other diagnoses should be made, such as low-grade mucinous tumor of the appendix, and any mucus present outside the appendix should not be diagnosed as appendiceal adenoma, even if it has no cellular component. Definition of appendiceal adenocarcinoma: malignant epithelial tumor of the appendix that infiltrates beyond the mucosal muscle layer. Appendiceal adenocarcinoma can be classified as non-mucinous (it has a similar biological behavior to the colonic carcinoma of the same name) and mucinous (when the extracellular mucus of appendiceal adenocarcinoma exceeds 50%, it is called mucinous adenocarcinoma). In patients with primary appendiceal adenocarcinoma, the appendix may be thickened, deformed, or completely destroyed. Due to the cystic dilatation caused by the collection of mucus in the appendiceal lumen, it may be called a mucinous cyst at this time, but this is a descriptive diagnosis, not a pathological one. Definition of mucinous adenocarcinoma: When the extracellular mucus of appendiceal adenocarcinoma exceeds 50%, it is called mucinous adenocarcinoma. Adenocarcinoma of the appendix is indistinguishable from acute appendicitis, in which most cases present as an abdominal or pelvic mass. CT can reliably demonstrate appendiceal adenomas and adenocarcinomas, characteristically presenting as cystic dilatation or soft tissue masses. The term peritoneal pseudomucinous tumor peritoneal pseudomucinous tumor refers to the slow and continuous production of mucus by tumorigenic mucus-secreting cells in the abdominal cavity I which accumulates and causes gelatinous ascites. the cells of LAMN have a mild morphology and float in the mucus. In most cases, the appendix is the primary site of mucinous adenocarcinoma from other organs such as colorectum, gallbladder, stomach, pancreas, fallopian tubes, umbilical ureter, lungs, and breast. Current evidence suggests that the ovary is very rare as a primary site, and the only cases are highly differentiated mucinous intestinal adenocarcinomas originating from mature cystic teratomas. Peritoneal pseudomucinous tumors can be classified as high-grade or low-grade. In general, low-grade peritoneal pseudomucinous tumors correspond to LAMN and high-grade lesions correspond to mucinous adenocarcinoma, although the opposite can occur. The unique feature of peritoneal pseudomucinous tumors, especially low-grade tumors, is their distribution in the abdomen: generally not in the peritoneum on the surface of the intestine, but more in the greater omentum, the right hemi-diaphragm, the right hemi-posterior hepatic space, the Treitz ligament, the left side of the abdomen, and the pelvis. When a patient has both an ovarian mucinous tumor and an appendiceal mucinous adenocarcinoma, molecular analysis suggests that the appendix is generally primary and the ovarian tumor is secondary to a low-grade or high-grade peritoneal pseudomucinous tumor are significantly different prognostic factors. Whether the mucus spread beyond the right lower 1/4 quadrant was an independent prognostic factor. If the mucus is anaplastic, the prognosis may improve.