Staging of appendiceal mucinous neoplasms: challenges and recent updates

Low-grade appendiceal mucinous neoplasms are unique tumors of the appendix, characterized by low-grade mucinous epithelium with villiform, undulating, or flat architecture. These tumors lack infiltrative growth or destructive invasion, but can extend into the appendiceal wall by a "pushing" pattern of invasion, with a broad front that can mimic a diverticulum. These neoplasms have a propensity for peritoneal dissemination, resulting in the clinical presentation of pseudomyxoma peritonei. The pathologic staging of these neoplasms is challenging and fraught with confusing terminology and numerous classification systems. This review focuses on the AJCC pathologic staging of these tumors with a focus on challenging situations.