Sunday 19 June 2016

Sigmoid Colon-Variation in Length and Location of the Sigmoid Colon-Cancer of the Sigmoid Colon-Volvulus--Diverticula-Sigmoidoscopy-Colonoscopy-Colostomy

Sigmoid Colon
The sigmoid colon begins as a continuation of the descending colon it is 10 to 15 in. (25 to 38 cm) long and lies in front of the pelvic brim. Below, it becomes continuous with the rectum in front of the 3rd sacral vertebra. The sigmoid colon is mobile and hangs down into the pelvic cavity in the form of a loop.
The sigmoid colon is attached to the posterior pelvic wall by the fan-shaped sigmoid mesocolon

 
Variation in Length and Location of the Sigmoid Colon
The sigmoid colon shows great variation in length and may measure as much as 36 in. (91 cm). In the young child, because the pelvis is small, this segment of the colon may lie mainly in the abdomen.

Cancer of the Sigmoid Colon
Because the lymphatic vessels of this segment of the colon drain ultimately into the inferior mesenteric nodes so The sigmoid colon is a common site for cancer of the large bowel. it follows that an extensive resection of the gut and its associated lymphatic field is necessary to extirpate the growth and its local lymphatic metastases. The colon is removed from the left colic flexure to the distal end of the sigmoid colon, and the transverse colon is anastomosed to the rectum.

Volvulus
Because of its extreme mobility, the sigmoid colon sometimes rotates around its mesentery. This may correct itself spontaneously, or the rotation may continue until the blood supply of the gut is cut off completely. The rotation commonly occurs in a counterclockwise direction and is referred to as volvulus.

 
Diverticula
The term diverticulitis refers to the inflammation of a diverticulum or diverticula, and this may result in perforation of the gut wall. Diverticula of the mucous membrane along the course of the arteries supplying the sigmoid colon is a common clinical condition and It consists of a herniation of the lining mucosa through the circular muscle between the teniae coli and occurs at points where the circular muscle is weakest. In patients with diverticulitis or ulcerative colitis, the sigmoid colon may become adherent to the bladder, rectum, ileum, or ureter and produce an internal fistula.

Sigmoidoscopy
Because the sigmoid colon lies only a short distance from the anus (6.5 in. [17 cm]), it is possible to examine the mucous membrane under direct vision for pathologic conditions. A flexible tube fitted with lenses and illuminated internally is introduced through the anus and carefully passed up through the anal canal, rectum, sigmoid colon, and descending colon. This examination, called sigmoidoscopy, can be carried out without an anesthetic in an outpatient clinic. Biopsy specimens of the mucous membrane can be obtained through this instrument.

Colonoscopy
Direct inspection of the lining of the entire colon including the cecum has become an important weapon in the early diagnosis of mucosal polyps and large bowel cancer in recent years.

Not only can the colon be observed and suspicious areas photographed for future reference, but also biopsy specimens can be removed for pathologic examination.
For the diagnosis of early cancer, physicians previously relied almost entirely on rectal examination, sigmoidoscopy, and the detection of occult blood in the feces. The disadvantage of colonoscopy is the high cost. Following a regime in which the large bowel is thoroughly washed out, the patient is relaxed under a light anesthetic. The flexible endoscopic tube is introduced through the anus into the anal canal, rectum, and colon. Colonoscopy can also be used in the diagnosis and treatment of ulcerative colitis and Crohn’s disease.

Colostomy
The sigmoid colon is often selected as a site for performing a colostomy in patients with carcinoma of the rectum. Its mobility allows the surgeon to bring out a loop of colon, with its blood supply intact, through a small incision in the left iliac region of the anterior abdominal wall. Its mobility also makes it suitable for implantation of the ureters after surgical removal of the bladder.









































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