Diagnosis: Mucinous cystic neoplasm of the appendix
• Primary mucinous appendiceal tumors are found in less than 2% of appendix resections. These tumors characteristically cause cystic dilatation of the appendix owing to accumulation of copious gelatinous material in the lumen.
• Mucinous appendiceal neoplasms display a circumferential growth pattern with a variable papillary architecture. The tumor cells often contain abundant cytoplasmic mucin and with mildly enlarged nuclei that are basally located, with minimal cytologic atypia.
• Pseudomyxoma peritonei (PMP) is a term used to describe mucinous ascites or mucin deposits within the peritoneal cavity. PMP consists of organizing pools of mucin within peritoneal fat or on the serosal surfaces of the viscera, which contain variable numbers of neoplastic epithelial cells. Most cases reflect dissemination of an appendiceal mucinous neoplasm, in which case, mucin pools that contain scant strips and clusters of low-grade neoplastic epithelial cells are typical.
• Cytologic grade should be specified when classifying PMP into low-grade mucinous carcinoma peritonei, and high-grade mucinous carcinoma peritonei. Bradley and colleagues found that low-grade mucinous carcinoma peritonei was associated with a significantly better 5-year survival rate (63%) than was high-grade mucinous carcinoma peritonei (38%).
• Treatment for a mucinous adenoma that has not ruptured and that is confined to the appendix is appendectomy. Treatment of mucinous tumors that have spread extensively into the abdomen, resulting in PMP, includes cytoreduction (debulking) surgery to remove mucin and tumor implants in the abdominal cavity followed by intraoperative peritoneal chemotherapy. In cases in which high-grade or poorly differentiated carcinoma is present, treatment includes systemic chemotherapy.
• The American Joint Committee on Cancer staging guidelines assign tumor (T) stage for appendiceal mucinous neoplasms similar to those used for colonic adenocarcinoma, with the exception that T4a denotes both serosal involvement and extra-appendiceal disease limited to the right lower quadrant. Mucinous deposits beyond the right lower quadrant (PMP) are considered to represent metastatic disease and are denoted as M1a.
