الفهرس 
Embryology and Anatomy of Colon and Rectum.Only 14 pages are availabe for public view
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Abstract
The goal of colorectal cancer surgery is complete removal of the tumor along with the major vascular pedicle feeding the affected colonic segment and the lymphatic drainage basin.
Although segmental resection alone may be sufficient for primary tumor removal, wider resection is generally needed to achieve a sufficient lymphadenectomy.
The purpose of screening for colorectal cancer is to eradicate potential cancers while they are still in the benign stage of the adenoma-carcinoma sequence. Screening also increases the likelihood of discovering existing cancers while they are still in the early stage.
People at increased risk for colorectal cancer including those with affected first-degree relatives, begin the screening at age 40 years rather than age 50 years, those with a family history of FAP or HNPCC, Genetic counseling and genetic testing are recommended to determine whether the person is a gene carrier, those with a personal history of adenomatous polyps, should have a repeat examination at 1 to 3 years. Patients who have colorectal cancer and undergo resection for cure should have a repeat colonoscopy after 1 year. Patients with long-standing IBD, should undergo colonoscopy every 1-2 years after 8 years of diffuse disease or after 15 years of localized disease.
Colorectal cancer prevention strategies are based on our understanding of colorectal carcinogenesis and availability of pharmacologic agents that are effective yet minimally toxic.Celecoxib, a selective cyclooxygenase-2inhibitor was effective in decreasing the number and size of polyps on serial colonoscopies. Although aspirin use has been proven to decrease colon cancer risk, this association may vary among population subgroups. Some recent trials focused on combined inhibition of polyamine production and cyclooxygenase inhibition. A recent report from a large randomized trial described a dramatic effect of this combination in reducing polyp recurrence in patients with prior history of colon polyps. But still confirmatory trials are ongoing.
Bleeding is the most common symptom of rectal cancer, occurring in 60% of patients, change in bowel habits is present in 43% of patients, large tumors can cause obstructive symptoms, tumors located low in the rectum can cause a feeling of incomplete evacuation and tenesmus, partial large-bowel obstruction may cause colicky abdominal pain and bloating, back pain is usually a late sign caused by a tumor invading or compressing nerve trunks. Urinary symptoms may also occur if the tumor is invading or compressing the bladder or prostate.Other manifestations include emergencies such as peritonitis from perforation (3%) or jaundice, which may occur with liver metastases (< 1%).
Physical examination is performed with specific attention to size and location of rectal cancer in addition to possible metastatic lesions, including enlarged lymph nodes or hepatomegaly.Digital rectal examination (DRE) provides an opportunity to readily detect abnormal lesions. Rectal tumors can be assessed for size, ulceration, and presence of any pararectal lymph nodes. Rigid proctoscopy is also performed to identify the exact location of the tumor in relation to the sphincter mechanism
Determination of optimal treatment plan for patients with colorectal cancer involves a complex decision-making process. Strong considerations should be given to the intent of surgery, possible functional outcome, and preservation of anal continence and genitourinary functions.Preservation of both anal and rectal reservoir function in treatment of rectal cancer is highly preferred by patients. Sphincter-saving procedures for rectal cancer are now considered the standard of care.
The local transanal excision including Transanal Endoscopic Microsurgery (TEM) of rectal cancer is reserved for early-stage cancers in a highly selected group of patients. When local recurrence is detected, patients usually have advanced disease, requiring extensive pelvic excisions. Therefore, strict selection criteria are essential when considering local excision.
Low anterior resection (LAR) with total mesorectum excision is generally performed for lesions in the middle and upper third of the rectum and, occasionally, for lesions in the lower third. Because this is a major operation, patients who undergo LAR should be in good health. They should not have any preexisting sphincter problems or evidence of extensive local disease in the pelvis. TME yields a lower local recurrence rate (4%) than transanal excision (20%), but it is associated with a higher rate of anastomotic leak (11%). For this reason, TME may not be necessary for lesions in the upper third of the rectum.
Abdominal perineal resection (APR) is performed in patients with lower-third rectal cancers and should be performed in patients in whom negative margin resection will result in loss of anal sphincter function. Disadvantages of APR includes, need for permanent colostomy, significantly higher short-term and long term morbidity and mortality, higher rate of sexual and urinary dysfunction.
Inadequate sampling of lymph nodes may reflect non-oncologic resection. The use of more extended pelvic lymphadenectomy has been studied for rectal cancer. Extended lymphadenectomy involves removal of all lymph nodes along the internal iliac and common iliac arteries. This procedure has been associated with significantly higher sexual and urinary dysfunction without any additional benefit in local recurrence especially in patients with adjuvant radiotherapy.
Recurrence after curative surgery for colorectal cancer remains a serious problem. Inadequate removal of the tumor is faraway the most important reason for recurrence. Surgical resection is the primary treatment modality for recurrent CRC, and outcome is most closely related to the extent of disease at presentation.
The liver is the most frequent site of blood borne metastases from primary colorectal cancers. In a subgroup of patients, the liver is the only site of recurrent disease, and surgical excision of the metastases is the only curative option for these patients.
A variety of ablative options for liver metastases are available today, including cryotherapy, radiofrequency, thermal, laser, and ultrasonic ablation aiming for the destruction of the intrahepatic neoplastic lesion. Of all the modalities, radiofrequency ablation (RFA) has dominated this group and is most studied.
Because the colon is drained solely by the portal system, one would not expect metastases to the lung without evidence of tumor in the liver. In contrast, rectal cancers may spread through the portal or systemic venous systems and can theoretically give rise to isolated pulmonary metastases. In select patients, particularly those with rectal cancers, resection of pulmonary recurrences can result in a 5 year survival rate of 20%.
Minimally invasive surgery has gained tremendous popularity following the success of laparoscopic cholecystectomy. The use of laparoscopy for large-bowel resection is technically challenging. But it certainly depends on the surgeon’s ability, knowledge of the anatomy, and experience with laparoscopy.
The laparoscopic approach to colorectal cancer is associated with decreased pain and narcotic use, earlier return of bowel function, reduced perioperative complications, shorter hospitalization and quicker convalescence when compared with the open approach.
The outcomes of laparoscopic and open approach in rectal cancer treatment are very similar. Particularly, mesorectal excision quality and colonic negative margins results have proven that the laparoscopic technique is safe and comparable to open surgery in rectal cancer treatment.
Robotic colorectal surgery is both safe and feasible. However, it has no clear advantages over standard laparoscopic colorectal surgery in terms of early postoperative outcomes or complications profile. However, the cost involved may restrict its use to patients with challenging rectal cancer and in specialist centers.