The adenoma grows as a slightly raised lesion. There are focal glandular architectural abnormalities as seen by basal gland disorientation and branching (11:00).
The base of the crypts are bulbous, a helpful architectural feature for identifying this lesion.
The appendix is thought to be a vestigial organ in the GI tract, although there is new evidence that it may function as a reservoir of gut flora which can repopulate the GI tract subsequent to an infection (Randall, Smith).
A number of serrated polyps of the colon are recognized, including hyperplastic polyp, sessile serrated adenoma, and traditional serrated adenoma. Much less is known about morphologically similar serrated lesions of the appendix, which have been described under a variety of overlapping names.
With respect to molecular characterization of serrated polyps of the appendix, Bellizzi et al did not detect abnormal nuclear localization of β-catenin in any of the cases of hyperplastic polyp or SSA, a finding confirmed by another study (Yantiss). Yantiss et al also found that loss of MLH-1 was frequent in serrated polyps but unassociated with MSI-H -- and that serrated lesions with dysplasia were less frequently associated with BRAF mutations.
In contrast, SSAs of the colon frequently display BRAF mutations or MSI-high pathway and thus, there is growing evidence that the molecular alterations of appendiceal SSAs may differ from its colonic counterpart -- but much work still needs to be done to fully characterize the pathogenesis, behavior and prognostic implications of appendiceal SSAs (Upton).
Colonic SSAs are markers of malignant transformation (similar to adenomatous polyps) and appendiceal SSAs may be even more strongly associated with malignancy, at least in one study. Rubio et al examined 38 non-carcinoid appendiceal neoplasms and found four hyperplastic polyps, 10 SSAs, 16 villous adenomas and 8 mucinous adenocarcinomas. 4/10 SSAs and 11/16 villous adenomas had progressed to invasive carcinoma.
Bellizzi AM, Rock J, Marsh WL, Frankel WL. Serrated lesions of the appendix: a morphologic and immunohistochemical appraisal. Am J Clin Pathol. 2010 Apr;133(4):623-32.
Randal Bollinger R, Barbas AS et al. Biofilms in the large bowel suggest an apparent function of the human vermiform appendix. J Theor Biol. 2007 Dec 21;249(4):826-31. Epub 2007 Sep 7.
Rubio CA. Serrated adenomas of the appendix. J Clin Pathol. 2004 Sep;57(9):946-9.
Upton MP. Looking through a keyhole: serrated neoplasia in the vermiform appendix. Am J Clin Pathol. 2010 Apr;133(4):529-32.
Yantiss RK,et al. A comprehensive study of nondysplastic and dysplastic serrated polyps of the vermiform appendix. Am J Surg Pathol. 2007;31:1742–1753.