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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