Produce mucin which dilates appendix into cystic or sausage shaped structure filled with mucin
This may rupture and cover the serosal surface
Sometimes mural calcification produces “ porcelain appendix”
Microscopy:
Circumferential proliferation of neoplastic mucinous epithelium which replaces normal epithelium
Epithelium may show different grades of dysplasia or invasion
Tumor cells have crowded tall columnar epithelium with basally located hyperchromatic pseudostratified nuclei and clear to eosinophilic cytoplasm having mucin vacuole
Mitotic activity is usually low
Classic pattern seen in these neoplasms is filiform villous architecture lined by tumor cells
Submucosa and muscularis show varying degrees hyalinization and fibrosis
Mucinous cystadenoma show minimal cytologic atypia. Term mucinous cystadenoma is no longer used. But now the term “ low grade mucinous neoplasm “ is used for the lesion with bland cytological features
Lesions with high grade cytological features are termed as “high grade mucinous neoplasm”
Mucinous lesion with dysplasia and infiltration are termed as mucinous adenocarcinoma
Intraluminal mucin may compress epithelium which appears flattened and its neoplastic nature could not be recognised
Increased luminal pressure due to accumulation of intraluminal mucin can cause diverticula or can rupture
After rupture mucin may spread on to the serosal surface and into peritoneal cavity
Mucin collected in the abdominal cavity along with tumor implants is called pseudomyxoma peritonei
Treatment and Prognosis:
Treatment is surgical excision
Recurrence rate is less than 5%
Recurrence rate in patients with presence of mucin in abdominal wall– 33% to 75%
Differential Dignosis:
Mucocele – benign mucoceles are usually less than 1cm in diameters larger lesions commonly indicates neoplastic process.