Subtitle: A step-by-step guide to grossing a total mesorectal excision specimen: grading the mesorectum, inking the CRM, slicing, block selection and the prognostic features you must report. Includes 10 interactive MCQs.
Author: PathologyMCQ Editorial Board
Category: GI Pathology / Grossing
Last Updated: October 2026
Read Time: 9 minutes
At-a-Glance
- Why it matters: the mesorectum is the main route of local spread, so the quality of its excision predicts local recurrence.
- Before you cut: photograph, grade the mesorectum (complete, nearly complete, incomplete) and ink the CRM.
- Open smartly: open anteriorly above and below the tumour; leave the tumour segment intact, fix, then slice transversely every 3–5 mm.
- Must report: CRM distance (involved if ≤1 mm), mesorectal grade, nodes (at least 12), EMVI, and regression score after neoadjuvant therapy.
The Mesorectum and Why TME Matters
The mesorectum is the fatty envelope around the rectum, enclosed by the mesorectal (visceral) fascia. It carries blood vessels, lymphatics and the regional lymph nodes, and it is the main route of local spread for rectal cancer. In a total mesorectal excision (TME) the surgeon dissects sharply in the plane outside this fascia, removing the rectum with an intact mesorectal package.
Clinical significance
- TME is the standard operation for mid and low rectal cancer.
- Dissection follows the avascular plane between the mesorectal fascia and the parietal (presacral) fascia, often called the “holy plane”.
- It removes the rectum, the intact mesorectum and its regional lymph nodes in one package.
- Compared with conventional surgery, published series report local recurrence falling from 20–30% to around 10% or less, with further reduction after neoadjuvant therapy, and better survival.
- The pathologist’s grading of the mesorectum is direct feedback on the quality of surgery.
Grading the Mesorectum (Quirke)
Grade the fresh, unopened specimen from all sides, before inking or cutting. Grade the worst area.
Complete
- Intact, bulky mesorectum with a smooth surface
- Only minor irregularities; no defect deeper than 5 mm
- No coning towards the distal margin
- Smooth, regular CRM on slicing
Nearly complete
- Moderate bulk with an irregular surface
- Defects deeper than 5 mm, but muscularis propria not visible
- Moderate coning
Incomplete
- Little bulk
- Defects reaching down to the muscularis propria
- Very irregular CRM on slicing
Coning is tapering of the mesorectum towards the distal end. It shows the surgeon came inside the mesorectal plane near the pelvic floor, and it raises the risk of an involved CRM.
Grossing a TME Specimen, Step by Step
Receive fresh and unopenedNote the procedure (anterior resection, LAR or APR), orientation stitches and any perforation.
Photograph anterior and posterior viewsBefore anything else, so the surgical plane is documented as received.
Grade the mesorectumComplete, nearly complete or incomplete, with coning and any defects described.
Ink the CRMPaint the non-peritonealised mesorectal surface. Identify the anterior peritoneal reflection and keep it separate in your description.
Open anteriorly, away from the tumourOpen above and below the tumour, leaving the tumour segment intact. Insert formalin-soaked gauze into the ends.
Fix thoroughlyAllow good fixation (commonly 48–72 hours or longer, per local protocol) so the fat slices cleanly.
Slice transversely every 3–5 mmLay the slices out in order from proximal to distal and photograph them. Measure the closest distance from tumour, deposits or nodes to the CRM.
Measurements and Description
| Parameter | What to record |
|---|---|
| Specimen and rectal length | In cm |
| Mesorectal envelope | Bulk, defects, smoothness; Quirke grade |
| Coning | Present or absent |
| Tumour size | Length × width × thickness, in cm |
| Distance to margins | Proximal and distal, in cm |
| Tumour location | Relation to the anterior peritoneal reflection: above, at or below; anterior or posterior |
| CRM | Closest distance in mm, and its clock position |
| Perforation | Present or absent, and its site |
Block Selection
| Tissue or region | Guideline |
|---|---|
| Tumour | At least 1 block per cm of tumour, or the whole tumour if small |
| Deepest invasion | At least 2 blocks |
| Closest CRM | At least 2 blocks, including the inked margin |
| Peritoneal surface | Blocks where tumour is close to the peritonealised surface |
| Treated tumour bed (post-neoadjuvant) | Generous sampling of the scar; submit entirely if no tumour is seen grossly |
| Proximal and distal margins | En face, or perpendicular if tumour is close |
| Lymph nodes | All nodes, in their entirety; bisect larger nodes |
| Apical node | Submit separately if identified |
| Nodes or deposits near the CRM | Record their distance to the CRM and clock position |
Photographs to Take
- Fresh specimen, anterior and posterior views
- All transverse slices laid out in order, proximal to distal
- Close-ups of tumour nearest the CRM, mesorectal defects and any involved nodes
Prognostic Features to Report
| Feature | Why it matters |
|---|---|
| CRM involvement (tumour ≤1 mm) | Strongest predictor of local recurrence; also lowers survival |
| Mesorectal grade | Poor (incomplete) excision predicts recurrence |
| EMVI and perineural invasion | Associated with distant metastasis and worse outcome |
| Tumour budding | Marker of aggressive behaviour |
| Lymph node yield (at least 12) | Quality benchmark for accurate staging |
| Tumour regression score (CAP, 0–3) | TRG 0 (no viable tumour) carries the best prognosis |
| Lymph node ratio | Proposed additional prognostic measure |
| Acellular mucin after therapy | Not counted as viable tumour or positive node |
Correction note: an earlier version of this article labelled the incomplete mesorectum as grade 3. Incomplete is grade 1; complete is grade 3.
Test Yourself: 10 MCQs
TME grossing: 10 MCQs
Planes, grading, inking, CRM, nodes and regression. Tap an answer for the explanation.
More practice: the GI pathology MCQ bank →
Exam Pearls
- Grade first, ink second, open third: never cut through the tumour segment before fixation.
- Complete = grade 3, nearly complete = grade 2, incomplete = grade 1.
- CRM involved = tumour ≤1 mm from the inked margin, by any route.
- The peritonealised anterior surface is not the CRM; tumour breaching it is pT4a.
- Acellular mucin after neoadjuvant therapy is not a positive node.
Video walkthrough
TME grossing, explained
Watch a TME specimen handled from start to finish: grading, inking, opening and slicing.
Ultimate FRCPath Part 2 Study Program
- Macro and grossing stations, with how examiners expect specimens to be described
- Timed short surgicals on virtual slides with model answers
- Long cases reported against the RCPath datasets
More courses
Preparing for an exam?
The Pathology MCQ app
A slide and an MCQ every day
Daily MCQ with streaks, pinch-zoom virtual slides with annotations, and your courses in one place.
Related reads: Rectal cancer grossing: anatomy, APR vs LAR and virtual slides →
Leave a Reply