The appendix, although considered a vestigial organ, is of considerable clinical importance because acute appendicitis is a common medical problem. There are also other disease processes involving the appendix. The appendix is among the first specimens that the pathologist (and surgeon) cuts one’s teeth on. Thus, there may be a tendency to underestimate the clinically and prognostically significant appendiceal pathologies.
We provide a vade mecum of the pathologic features of a wide range of nonneoplastic appendiceal pathologies, with an emphasis on developing a practical approach to grossing, microscopy, and reporting-all with clinical and therapeutic implications. Much of this is based on literature on MEDLINE with reference to years 2008 to 2023, as well as on personal experiences and interpretations.
The appendix can harbor a myriad of nonneoplastic pathologies, including infections, inflammations of varying etiologies (including interval appendectomy), endometriosis, diverticulosis, and so on. Chronic appendicitis, Crohn disease, and clinical audit are recurring themes while COVID-19 is a new entity.
Most importantly, all pathologists should appreciate that the appendix is not as “routine” a specimen as one would want to believe.

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