Overview
Definition:
Total Mesocolic Excision (TME) is a surgical technique that aims to resect the entire mesocolon, including its central vascular pedicles and associated lymphatic tissue, in continuity with the segment of the colon being removed
This approach emphasizes anatomical dissection along defined embryological planes, theoretically achieving a higher oncological clearance for colorectal malignancies.
Historical Context:
The concept of TME gained prominence with the work of Richard J
Heald and others, emphasizing en bloc resection and anatomical dissection
Early techniques focused on achieving negative margins, but modern TME incorporates a precise understanding of embryological planes and vascular supply to optimize oncological outcomes and reduce local recurrence rates.
Clinical Significance:
TME is crucial for achieving optimal oncological outcomes in colorectal cancer surgery, particularly for right-sided colon cancers
It aims to improve local recurrence rates and overall survival by ensuring complete removal of the tumor and its regional lymph nodes within the mesocolic envelope
Understanding the precise planes and vascular pedicles is paramount for safe and effective execution of this procedure, directly impacting patient care and treatment success.
Embryological Basis And Planes
Embryological Development:
The colon develops from the midgut and hindgut
The mesocolon, which anchors the colon to the posterior abdominal wall, is formed by fusion of the visceral peritoneum with the parietal peritoneum
TME dissection follows planes that respect these embryological fusion lines.
Right Hemicolectomy Plane:
For right-sided lesions (cecum, ascending colon, hepatic flexure), the dissection plane typically lies between the superior mesenteric artery (SMA) and the mesentery of the small intestine
The plane separates the colon from the retroperitoneum, preserving the duodenum, pancreas, and right ureter
The dissection is typically centered on the ileocolic artery and the right colic artery (or its origin from the SMA).
Left Hemicolectomy Plane:
For left-sided lesions (splenic flexure, descending colon, sigmoid colon), the dissection plane lies between the inferior mesenteric artery (IMA) and the descending colon mesentery
This plane respects the fusion of the mesentery of the descending colon to the retroperitoneum, preserving the left ureter, gonadal vessels, and spleen
The dissection is usually centered on the left colic artery (or its origin from the IMA).
Central Vascular Division:
A key principle of TME is the central division of the major vascular pedicles (ileocolic, right colic, middle colic for right TME
left colic, sigmoid branches for left TME) at their origin from the SMA or IMA
This ensures complete removal of the mesentery and lymphatics in an en bloc fashion.
Importance Of Plane Adherence:
Dissecting strictly within these embryologically defined planes is critical to avoid inadvertent injury to adjacent structures such as the duodenum, pancreas, aorta, vena cava, and ureters
It also ensures complete mesocolic resection and minimizes tumor spillage.
Vascular Pedicles And Landmarks
Superior Mesenteric Artery Supply:
The SMA supplies the right colon
Key branches for TME include the ileocolic artery (supplying the cecum and terminal ileum), the right colic artery (supplying the ascending colon), and the middle colic artery (supplying the transverse colon).
Inferior Mesenteric Artery Supply:
The IMA supplies the left colon
Key branches include the left colic artery (supplying the descending colon) and sigmoid arteries (supplying the sigmoid colon).
Landmarks For Dissection:
For right TME, the SMA and its branching pattern, the duodenum, head of pancreas, and the right ureter are critical landmarks
For left TME, the IMA origin, aorta, left renal vein, left ureter, and gonadal vessels are important.
Central Vascular Control:
Accurate identification and ligation of the main vascular pedicle (e.g., ileocolic artery and vein, right colic artery and vein, etc.) at their origin from the SMA or IMA is fundamental to TME
This allows for mobilization of the colon with its entire mesentery.
Importance Of Venous Drainage:
Understanding the venous drainage (e.g., ileocolic vein, right colic vein draining into the SMV
left colic vein draining into the IMV) is equally important for achieving complete oncological resection and preventing venous tumor embolization.
Surgical Technique And Considerations
Preoperative Assessment:
Detailed imaging (CT scan, MRI) to assess tumor resectability, involvement of adjacent structures, and lymph node status
Multidisciplinary team discussion is essential.
Approach Laparoscopic Vs Open:
TME can be performed laparoscopically or openly
Laparoscopic TME requires advanced skills but offers potential benefits such as reduced pain and faster recovery
The principles of anatomical dissection and plane identification remain the same.
Mobilization And Dissection:
The dissection begins by mobilizing the colon from the retroperitoneum along the defined embryological plane
Careful electrocautery or harmonic scalpel use is employed to divide the vascular branches and mesentery.
En Bloc Resection:
The goal is to remove the involved colonic segment with its entire mesentery and associated lymph nodes as a single specimen
This requires careful attention to the vascular pedicles and dissection planes throughout the procedure.
Anastomosis:
After resection, an anastomosis is performed, typically between the remaining bowel segments or between the bowel and a stoma, depending on the extent of resection and patient factors
Stapled or hand-sewn techniques are used.
Indications And Contraindications
Indications:
Primary indication is for resectable colorectal cancer, especially right-sided colon tumors, where complete mesocolic excision is deemed necessary for optimal oncological clearance
Also considered for certain inflammatory conditions or polyposis syndromes requiring extensive resection.
Contraindications:
Absolute contraindications include unresectable disease, distant metastases, significant comorbidities precluding major surgery, or extensive local invasion into vital structures that cannot be safely dissected
Relative contraindications may include severe adhesions or inflammatory changes obscuring anatomical planes.
Patient Selection:
Careful patient selection is crucial
Patients should be assessed for fitness for major abdominal surgery
The absence of extensive extra-mesenteric spread is generally required for TME to be oncologically effective.
Complications And Outcomes
Anastomotic Leak:
The most feared complication, occurring in 3-5% of cases
Risk factors include poor vascularity, technical issues, and patient comorbidities
Meticulous surgical technique and careful patient selection are key to prevention.
Intraoperative Injuries:
Injury to adjacent organs such as the duodenum, pancreas, small bowel, ureters, aorta, or vena cava can occur if dissection planes are not adhered to
Careful surgical technique and identification of landmarks are vital.
Bleeding:
Bleeding from major vessels or mesenteric vessels can occur
Careful ligation of vascular pedicles and adequate hemostasis are essential.
Infection:
Wound infection and intra-abdominal abscesses are potential complications, managed with antibiotics and drainage if necessary.
Outcomes:
When performed appropriately, TME can lead to improved local control rates and potentially better survival for colorectal cancer patients compared to less radical resections
However, outcomes are highly dependent on the stage of disease and surgical expertise.
Key Points
Exam Focus:
Understand the embryological planes for right and left TME
Know the key vascular pedicles and their origins (SMA/IMA)
Recognize the critical surrounding structures to preserve
Differentiate between standard colectomy and TME in terms of oncological principles.
Clinical Pearls:
Start dissection at a safe avascular plane
Identify the SMV/IMV and follow it proximally to the SMA/IMA to ensure correct vascular pedicle division
Always confirm preservation of the duodenum, pancreas, and ureters
Consider central vascular ligation at the earliest opportunity during mobilization.
Common Mistakes:
Dissecting outside the correct embryological plane, leading to injury of adjacent organs
Incomplete mesocolic excision due to inadequate mobilization or failure to ligate central vascular pedicles
Unnecessary ligation of secondary branches of the SMA/IMA leading to bowel ischemia.