Mesorectal Excision for Rectal Cancer - An Overview

Introduction

Total mesorectal excision for rectal cancer is a surgical procedure of removal of cancer tissue along with the surrounding perirectal lymphatic tissue. With the help of new diagnostic procedures such as ectosigmoidoscopy can help detect cancer in its early stage. The treatment has multiple approaches, such as surgery, chemotherapy, and radiotherapy for post and pre-operative cases. Total mesorectal excision surgical procedure has reduced local recurrence rates and has improved outcomes.

What Is a Rectal Cancer?

A malignant neoplasm that starts in the rectum is called rectal cancer, the last part of the large intestine. When the colon is involved, it is called colon cancer; together, it is known as colorectal cancer. Rectal cancer is the second most cancer after colon cancer, affecting the large intestine.

What Are the Symptoms of a Rectal Cancer?

The symptoms of rectal cancer include:

• Rectal bleeding is the most common symptom.

• Extension of the tumor into adjacent organs in case of advanced-stage of cancer.

• Tenesmus (feeling to pass the stools, even though it is empty).

• Rectal, abdominal, or pelvic pain.

• Incomplete bowel movement and change in bowel habits.

• Pencil thin stools.

• Hematochezia (blood in the stools).

• Iron deficiency anemia is common in right-sided rectal cancers.

• Metastasis can occur in the liver, lungs, and bone.

• Intestinal obstruction.

• Peritonitis (inflammation of the peritoneum that lines the abdominal cavity).

• Fistula (an abnormal connection between the organs) into adjacent organs such as the bladder.

• Abscess around perforated cancer.

• Bacteremia (a condition where bacteria is present in the blood).

• Sepsis (extreme reaction to the infection, which causes fever, fast heart rate, difficulty breathing, mental confusion, etc.).

• Fever.

What Is the Diagnosis of Rectal Cancer?

The diagnosis of rectal cancer includes signs, symptoms and by rectal examination, which are:

• Colonoscopy is used for biopsy and evaluating polyps and tumors.

• Ectosigmoidoscopy (a diagnostic test of the lower colon which is done with the help of a sigmoidoscope, a thin instrument with lens and light to view).

• Double-contrast barium enema (DCBE, a diagnostic procedure of colon and rectum X-ray with the help of barium which helps in outlining the structures).

• Computed tomographic colonography (CTC) is a non-invasive diagnostic method examining extracolonic organs.

• Magnetic resonance imaging (MRI) and endoscopic ultrasound determine the cancer stage.

• Serum markers such as carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 (CA 19-9) can be used.

What Is Total Mesorectal Excision for Rectal Cancer?

Total mesorectal excision involves the removal of the entire tumor along with the lymphatic vessels, which are contained in the mesorectum (a fatty tissue layer that contains lymph nodes and blood vessels which is present adjacent to the rectum). Total mesorectal excision is the standard surgical treatment, where the perirectal areolar tissue and the mesorectal’s lateral and circumferential margins are removed using sharp dissection. Five centimeters beyond the rectal tumor is excised.

What Is the Technique of Total Mesorectal Excision?

The pre-operative evaluation should contain detailed history and physical examination. A digital rectal exam and a rigid proctoscopy should be done, which precisely measures the tumor’s distance from the anal verge. The size of the tumor is determined with the help of transrectal ultrasound (TRUS). The surgical technique involves:

• Before the surgery, the stoma site should be marked by an enterostomal therapist, sequential compression devices (SCDs) should be started before giving general anesthesia to avoid deep vein thrombosis, and intravenous antibodies should be given one hour before skin incision.

• Surgery is performed with the patient in a modified-lithotomy position, a foley catheter is placed, and saline and povidone-iodine irrigation is done in the rectum.

• Any dissection on the rectum is performed sharply, preventing the mesorectum's disruption and the tumor's spread.

• A midline incision is made, the peritoneal cavity is opened, and the liver is evaluated for metastasis. Next, the incision is made between the colonic mesentery, and the retroperitoneum is opened.

• After the colon's mobilization, the inferior mesenteric artery, nerve fibers of the preaortic sympathetic/superior hypogastric plexus, and left colic artery are divided and ligated. Dissection is done up to the distal edge of the colon along the course of the left colic artery, which will provide collateral blood supply. The dissection plane is between the investing fascia of the mesorectum and the presacral fascia; hypogastric nerves are preserved at this point. An electrocautery is used for dissection, and the tissues are stretched using the blades of a Kelly clamp.

• Further anterior peritoneal dissection is done between the anterior wall of the rectum and the lower uterus.

• If the tumor is present in the anterior wall of the rectum, the peritoneum is incised anteriorly.

• For posterior tumors, dissection is done posterior to the peritoneal reflection and between the anterior rectal wall and Denonvilliers' fascia, which is made in a U shape to avoid nerve injury.

• After the rectum's complete mobilization, the tumor's distal margin is divided, and anastomosis is carried out. An adequate distal margin of 5 centimeters and radial margins of more than one millimeter should be divided.

• The patient is placed in a jack-knife position, using a pursestring suture; the anus is closed to prevent extrusion of tumor cells and a diamond-shaped incision is made around the anus and deepened into the ischiorectal fossa .proximal end of the rectum is brought through the posterior perineal wound, then anterior dissection is completed.

• After removal of the tumor tissue, the deep tissues of the perineal are irrigated, interrupted figure-of-eight sutures are placed, and the skin is loosely approximated and sutured.

This surgical technique preserves pelvic autonomic nerves, reduces the risk of post-operative genitourinary dysfunction, and has a low recurrence rate and increased survival rate. However, complications such as anastomotic leaks may occur.

What Are the Other Treatments for Rectal Cancer?

The other surgical treatments for rectal cancer include:

• Local Excision: This is done in case of distal rectal tumors, which are non-aggressive. Transanal excision is the most common local excision, which involves the excision of full-thickness rectal cancer with a minimum lateral margin of 1 cm and a deep negative margin.

• Low Anterior Resections (Sphincter-Sparing Procedures): This procedure is done in case of tumors in the rectum's upper or middle parts.

• Abdominoperineal Resection: This is indicated in low rectal tumors, with no space between the sphincter and the tumor. The sigmoid colon, rectum, and anus are removed, followed by a permanent colostomy.

• Neoadjuvant Therapy: This is indicated in cancers in the middle or distal rectum. Along with mesorectal excision, short-course radiotherapy (SCRT) and long-course chemoradiotherapy (LCCRT) are given. This approach has a low recurrence rate.

Conclusion

The prognosis depends on the cancer’s stage while performing surgery and the behavior of the cancer. The recurrence of rectal cancer depends on the surgical approach and proper patient selection. Neoadjuvant therapy and total mesorectal excision provided added benefits and improved the surgical procedure.