Microscopy: The sections were taken through the appendiceal wall show obliteration of the submucosa, with mucinous epithelial lesion with a villiform architecture resting directly on the muscularis propria. The lining cells show nuclear crowding and mild stratification, coarse nuclear chromatin and tall apical cytoplasm containing mucin. There is the preservation of polarity to the basement membrane. The lumen contains large quantities of focally calcified, acellular mucin. At the site of rupture, acellular mucin dissects through the wall of the appendix and is present at the serosal surface, with an associated serosal reaction including mesothelial hyperplasia, a florid fibroblastic response and fibrin deposition on the serosal surface. Acellular mucin is also seen in the extruded material sampled over the appendiceal tip. Focally at the tip, mucin at the serosal surface contains clusters of low-grade neoplastic epithelial cells. Foci of chronic inflammation, including clustered lymphocytes, scattered multinucleated giant cells and granulomatous inflammation, are present within the wall. In areas, dense fibrosis replaces mural structures, including the muscularis propria, and there is acellular dissecting mural mucin.The lesion is clear of the proximal and distal margins, and there are no other mucosal abnormalities. There is no metastatic disease in regional lymph nodes.
Conclusion: Ruptured low-grade appendiceal mucinous neoplasm (LAMN), 90mm; low-grade dysplastic epithelium within extra-appendiceal mucin; negative resection margins; no metastatic disease in 20 regional lymph nodes.