Pathologic examination and staging of rectal carcinoma: a critical review

In rectal carcinoma, accurate pathological examination is crucial for a correct staging and identification of predictors of risk of both local recurrence and overall survival. Accordingly, surgical pathologists determine many facets of rectal carcinoma patient care. Although rectal carcinoma shares many pathologic features with colon carcinoma, however, the anatomical location of the rectum poses additional problems in formulation of a pathological report. The most critical issues of pathological examination in rectal carcinoma involve assessment of: i) surgical resection margins (distal and circumferential resection margins); ii) total mesorectal excision (the plane of surgery); iii) peritoneal serosa involvement; iv) distance of invasion beyond the muscularis propria; v) number of lymph nodes to be recovered; vi) mesorectal tumor deposits; and vii) histologic regression grade after preoperative chemoradiotherapy. Although seemingly straightforward, the definition and macroscopic/microscopic interpretation of these key pathological features are still controversial, and lead to pathological reports that are variable not only among the different institutions but even within a single institution. The aim of this critical review on rectal carcinoma is to discuss confusing and/or challenging pathological problems, especially those with clinical impact, in order to provide a checklist that is useful for practicing surgical pathologists.