Excision Margins

Doughnuts/anastomotic rings/staple gun transections—involved/not involved.

Distances to the: nearest longitudinal resection limit (mm); mesorectal CRM (mm); mesocolic resection margin (mm).

Longitudinal spread beyond the gross edge of a colorectal carcinoma is unusual (<5% of cases) and anterior resection of rectal carcinoma is generally considered satisfactory if a macroscopic clearance of 2-3 cm beyond the lesion edge is feasible.

Block the nearest longitudinal surgical margin if <3 cm from the tumour edge, or if >3 cm but with any of: an unusually infiltrative tumour margin, extensive lymphovascular or mesorectal invasion or morphology such as signet ring cell, small cell, undifferentiated carcinoma.

CRM involvement = direct or discontinuous tumour spread, or tumour within a lymphatic, node or vessel <1 mm from the painted margin. Distances to this margin are best assessed using transverse serial slices of the resection specimen. Note that non-peritonealized CRMs exist not only in the mesorectum but also where the superior mesorectum joins the inferior aspect of the sigmoid mesentery, and in relation to the posterior aspects of the proximal ascending colon and descending colon.

The prognostic significance of mesocolic margin involvement has not been fully clarified but is clearly an index of spread of disease and/or adequacy of surgery.

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