Colon, rectum, and anus

Colon, Rectum, and
Anus
By Dr Mengistu.K

Embryology
• The primitive gut is derived from the endoderm
and divided into three segments: foregut,
midgut, and hindgut.
• Both midgut and hindgut contribute to the colon,
rectum, and anus.
• The midgut develops into the small intestine,
ascending colon, and proximal transverse colon,
and receives blood supply from the superior
mesenteric artery.
7/30/2016 Dr.mengistu 2

• During the sixth week of gestation, the midgut
herniates out of the abdominal cavity, and then
rotates 270° counterclockwise around the
superior mesenteric artery to return to its final
position inside the abdominal cavity during the
tenth week of gestation.

• During the sixth week of gestation, the distal-
most end of the hindgut, the cloaca, is divided
by the urorectal septum into the urogenital sinus
and the rectum.
• The distal anal canal is derived from ectoderm
and receives its blood supply from the internal
pudendal artery.
• The dentate line divides the endodermal hindgut
from the ectodermal distal anal canal.

Anatomy
• The wall of the colon and rectum comprise five
distinct layers: mucosa, submucosa, inner
circular muscle, outer longitudinal muscle, and
serosa.
• In the distal rectum, the inner smooth muscle
layer coalesces to form the internal anal
sphincter.
• The intraperitoneal colon and proximal one-
third of the rectum are covered by serosa; the
mid and lower rectum lack serosa.

Colon Landmarks
• The rectosigmoid junction is found at
approximately the level of the sacral promontory
and is arbitrarily described as the point at which
the three teniae coli coalesce to form the outer
longitudinal smooth muscle layer of the rectum.
• The cecum is the widest diameter portion of the
colon (normally 7.5–8.5 cm) and has the thinnest
muscular wall. As a result, the cecum is most
vulnerable to perforation and least vulnerable to
obstruction.

• The attachments between the splenic flexure and
the spleen (the lienocolic ligament) can be short
and dense, making mobilization of this flexure
during colectomy challenging.
• The sigmoid colon is the narrowest part of the
large intestine and is extremely mobile.
• The narrow caliber of the sigmoid colon makes
this segment of the large intestine the most
vulnerable to obstruction.

Colon Vascular Supply
 Ileo-colic artery is absent in up to 20% of people

• The terminal branches of each artery form
anastomoses with the terminal branches of the
adjacent artery and communicate via the
marginal artery of Drummond. This arcade is
complete in only 15% to 20% of people.

Colon Nerve Supply
• Sympathetic nerves arise from T6-T12 and L1-
L3.
• The parasympathetic innervation to the right
and transverse colon is from the vagus nerve.
• The parasympathetic nerves to the left colon
arise from sacral nerves S2-S4 to form the
nervi erigentes.

Anorectal Landmarks
• The rectum is approximately 12 to 15 cm in
length.
• At S4, the rectosacral fascia (Waldeyer’s fascia)
extends forward and downward and attaches to
the fascia propria at the anorectal junction.
• Denonvilliers’fascia separates the rectum from
the prostate and seminal vesicles in men and
from the vagina in women.

• The dentate or pectinate line marks the
transition point between columnar rectal mucosa
and squamous anoderm.
• The dentate line is surrounded by longitudinal
mucosal folds, known as the columns of
Morgagni, into which the anal crypts empty.
• The surgical anal canal measures 2 to 4 cm in
length and is generally longer in men than in
women.

• The venous drainage of the rectum parallels
the arterial supply.

• Lymphatic drainage of the rectum parallels the
vascular supply.
• The upper and middle rectum drain superiorly
into the inferior mesenteric lymph nodes.
• The lower rectum drain both superiorly into
the inferior mesenteric lymph nodes and
laterally into the internal iliac lymph nodes.

• Anal canal: proximal to the dentate line, lymph
drains into both the inferior mesenteric lymph
nodes and the internal iliac lymph nodes.
• Distal to the dentate line, lymph primarily
drains into the inguinal lymph nodes, but can
also drain into the inferior mesenteric lymph
nodes and internal iliac lymph nodes.

Anorectal Nerve Supply.
• Sympathetic nerve fibers are derived from L1-L3 and
join the preaortic plexus………extend below the
aorta to form the hypogastric plexus,….joins the
parasympathetic fibers to form the pelvic plexus.
• Parasympathetic nerve fibers originate from S2-S4.
• The internal anal sphincter is innervated by
sympathetic and parasympathetic nerve fibers; both
types of fibers inhibit sphincter contraction.

• The external anal sphincter and puborectalis
muscles are innervated by the inferior rectal
branch of the internal pudendal nerve.
• Sensory innervation to the anal canal is
provided by the inferior rectal branch of the
pudendal nerve.

NORMAL PHYSIOLOGY
• The colon is a major site for water absorption and
electrolyte exchange.
• Under normal circumstances, approximately 90%
of the water contained in ileal fluid is absorbed in
the colon (1000–2000 mL/d), but up to 5000 mL
of fluid can be absorbed daily.
• Sodium is absorbed actively via sodiumpotassium
(Na+/K+) ATPase.
• The colon can absorb up to 400 mEq of sodium
per day.

• Water accompanies the transported sodium and
is absorbed passively along an osmotic
gradient.
• Potassium is actively secreted into the colonic
lumen and absorbed by passive diffusion.
• Chloride is absorbed actively via a chloride
bicarbonate exchange.

Colonic Microflora and Intestinal Gas
• Approximately 30% of fecal dry weight is
composed of bacteria (1011–1012 bacteria/g of
feces).
• Anaerobes are the predominant class of
microorganism, and Bacteroides species are the
most common (1011–1012 organisms/mL).
• Escherichia coli are the most numerous aerobes
(108–1010 organisms/mL).

Colonic gas
• Nitrogen and oxygen are largely derived from swallowed
air.
• Carbon dioxide is produced by the reaction of
bicarbonate and hydrogen ions and by the digestion of
triglycerides to fatty acids.
• Hydrogen and methane are produced by colonic bacteria.
The production of methane is highly variable.
• The gastrointestinal tract usually contains between 100
and 200 mL of gas, and 400 to 1200 mL/d are released as
flatus, depending on the type of food ingested.

CLINICAL EVALUATION
• Clinical Assessment: Hx and P/E
• Anoscopy: measure approximately 8 cm in length.
• Proctoscopy: useful for examination of the rectum and
distal sigmoid colon. The standard proctoscope is 25 cm
in length and available in various diameters.
• Flexible Sigmoidoscopy: provide excellent visualization
of the colon and rectum. Measure 60 cm in length.
• Colonoscopy: measure 100 to 160 cm in length and are
capable of examining the entire colon and terminal ileum.

• Double-contrast barium enema (use of barium
followed by the insufflation of air into the colon) has
been reported to be 70% to 90% sensitive for the
detection of mass lesions greater than 1 cm in
diameter.
• For detection of small lesions colonoscopy is
preferred
• Endorectal ultrasound is primarily used to evaluate
the depth of invasion of neoplastic lesions in the
rectum.
• Overall,the accuracy of ultrasound in detecting
depth of mural invasion ranges b/n 81% and 94%

Physiologic and Pelvic Floor
Investigations
• Manometry: Anorectal manometry is performed
by placing a pressure-sensitive catheter in the lower
rectum.
• The resting pressure in the anal canal reflects the
function of the internal anal sphincter (normal, 40–
80 mmHg)
• Whereas the squeeze pressure,reflects function of
the external anal sphincter (normal, 40–80 mmHg
above resting pressure).
• The high-pressure zone estimates the length of the
anal canal (normal, 2.0–4.0 cm).
Squeeze pressur = maximum voluntary contraction pressure
minus the resting pressure

• Tumor markers: Carcinoembryonic antigen
(CEA) may be elevated in 60% to 90% of
patients with colorectal cancer but non
specific.

• GENERAL SURGICAL CONSIDERATIONS

Resections
• For left-sided tumors, the traditional approach
has involved resection of the involved bowel
and end colostomy, with or without a mucus
fistula.
• If the proximal colon appears unhealthy
(vascular compromise, serosal tears,
perforation), a subtotal colectomy can be
performed with a small bowel to rectosigmoid
anastomosis

• Ileocolic Resection: a limited resection of the
terminal ileum, cecum, and appendix. The ileocolic
vessels are ligated and divided
• Right Colectomy:
– used to remove lesions or disease in the right colon
– oncologically the most appropriate operation for curative
intent resection of proximal colon carcinoma.
– The ileocolic vessels, right colic vessels, and right
branches of the middle colic vessels are ligated and
divided.
– Approximately 10 cm of terminal ileum are usually
included in the resection.

• Extended Right Colectomy
– The right colon and proximal transverse colon are
resected, and a primary anastomosis is created
between the distal ileum and distal transverse colon.
– A standard right colectomy is extended to include
ligation of the middle colic vessels at their base.
– Such an anastomosis relies on the marginal artery of
Drummond.

• Left Colectomy
– For lesions or disease states confined to the distal
transverse colon, splenic flexure, or descending
colon
– The left branches of the middle colic vessels, the
left colic vessels, and the first branches of the
sigmoid vessels are ligated.
– A colocolonic anastomosis can usually be
performed

• Extended Left Colectomy.
– An option for removing lesions in the distal
transverse colon.
– In this operation, the left colectomy is extended
proximally to include the right branches of the
middle colic vessels.
• Sigmoidectomy

Proctocolectomy
• Total Proctocolectomy. the entire colon, rectum, and anus
are removed and the ileum is brought to the skin as a
Brooke ileostomy.
• Restorative Proctocolectomy (Ileal Pouch–Anal
Anastomosis).
– The entire colon and rectum are resected, but the anal
sphincter muscles and a variable portion of the distal anal
canal are preserved.
– Bowel continuity is restored by anastomosis of an ileal
reservoir to the anal canal.
– The neorectum is made by anastomosis of the terminal ileum
aligned in a “J,” “S,” or “W” configuration.
– J-pouch is the simplest to construct, it has become the most
used configuration.

• Anterior Resection
– Resection of the rectum from an abdominal
approach to the pelvis with no need for a perineal,
sacral other incision.
– Three types
High Anterior Resection
Low Anterior Resection
Extended Low Anterior Resection

• High Anterior Resection.
– resection of the distal sigmoid colon and upper rectum
– appropriate operation for benign lesions and disease at the
rectosigmoid junction such as diverticulitis.
– The upper rectum is mobilized, but the pelvic peritoneum is
not divided and the rectum is not mobilized fully from the
concavity of the sacrum.
– The inferior mesenteric artery is ligated at its base, and the
inferior mesenteric vein is ligated separately.
– A primary anastomosis (usually end-to-end) between the
colon and rectal stump

• Low Anterior Resection
– Used to remove lesions in the upper and mid rectum.
– The rectosigmoid is mobilized, the pelvic
peritoneum is opened, and the inferior mesenteric
artery is ligated and divided
– The rectum is mobilized from the sacrum by sharp
dissection.
– The dissection may be performed distally to the
anorectal ring, extending posteriorly through the
rectosacral fascia to the coccyx and

– anteriorly through Denonvilliers’ fascia to the vagina
in women or the seminal vesicles and prostate in
men.
– A low rectal anastomosis usually requires
mobilization of the splenic flexure and ligation and
division of the inferior mesenteric vein just inferior
to the pancreas.

• Extended Low Anterior Resection.
– Necessary to remove lesions located in the distal
rectum, but several centimeters above the
sphincter.
– The rectum is fully mobilized to the level of the
levator ani muscle just as for a low anterior
resection, but the anterior dissection is extended
along the rectovaginal septum in women and distal
to the seminal vesicles and prostate in men.

• Abdominoperineal Resection(APR)
– Involves removal of the entire rectum, anal canal,
and anus with construction of a permanent
colostomy from the descending or sigmoid colon.

INFLAMMATORY BOWEL DISEASE
• Inflammatory bowel disease includes ulcerative
colitis, Crohn’s disease, and indeterminate
colitis.
• Ulcerative colitis occurs in 8 to 15 people per
100,000 in the United States.
• Ulcerative colitis incidence peaks during the
third decade of life and again in the seventh
decade of life.
• The incidence of Crohn’s disease is slightly
lower, 1 to 5 people per 100,000.

• Crohn’s disease has a similar bimodal
incidence, with most cases occurring between
ages 15 to 30 years and ages 55 to 60 years.
• In 15% of patients with inflammatory bowel
disease are classified as having indeterminate
colitis. Patients typically present with
symptoms similar to ulcerative colitis.

Etiology
• Environmental factor such as diet or infection.
• Alcohol and oral contraceptive
• Smoking has been implicated in the etiology and
exacerbation of Crohn’s disease in particular.
• Family history may play a role in 10% to 30%
of patients.
• Gut mucosal barrier.

Pathology and Differential Diagnosis
• Ulcerative colitis is a mucosal process in which
the colonic mucosa and submucosa are
infiltrated with inflammatory cells.
• The mucosa may be atrophic, and crypt
abscesses are common.
• Endoscopically, the mucosa is frequently friable
and may possess multiple inflammatory
pseudopolyps.

• Ulcerative colitis does not involve the small
intestine, but the terminal ileum may
demonstrate inflammatory changes
(“backwash ileitis”).
• A key feature of ulcerative colitis is the
continuous involvement of the rectum and
colon; rectal sparing or skip lesions suggest a
diagnosis of Crohn’s disease.

• Patients typically complain of bloody diarrhea
and crampy abdominal pain.
• Proctitis may produce tenesmus.
• Severe abdominal pain and fever raise the
concern of fulminant colitis or toxic megacolon

• Crohn’s disease is a transmural inflammatory
process that can affect any part of the
gastrointestinal tract from mouth to anus.
• Mucosal ulcerations, an inflammatory cell
infiltrate, and noncaseating granulomas are
characteristic pathologic findings.
• Chronic inflammation may ultimately result in
fibrosis, strictures, and fistulas in either the
colon or small intestine.

• Chronic inflammation in Crohn’s may ultimately
result in fibrosis, strictures, and fistulas in either
the colon or small intestine.
• Extraintestinal Manifestations
– The liver is a common site
– Fatty infiltration of the liver is present in 40% to 50%
of patients, and cirrhosis is found in 2% to 5%.
– Primary sclerosing cholangitis: 40% to 60% of
patients have ulcerative colitis. The only effective
therapy is liver transplantation

– Bile duct carcinoma is a rare complication of long-
standing inflammatory bowel disease.
– Patients are 20 years younger than other patients
with bile duct carcinoma.
– Arthritis(Sacroiliitis and ankylosing spondylitis):
incidence is 20 times greater than in the general
population.

– Erythema nodosum is seen in 5% to 15% of pt.
Women are affected three to four times more
frequently than men. The characteristic lesions are
raised, red, and predominantly on the lower legs.
– Pyoderma gangrenosum: the lesion begins as an
erythematous plaque, papule, or bleb, usually
located on the pretibial region of the leg and
occasionally near a stoma.
– Up to 10% of patients with inflammatory bowel
disease will develop ocular lesions.

Principles of Nonoperative
Management
• Focuses on decreasing inflammation and
alleviating symptoms
• Salicylates
– first-line agents in the medical treatment of mild to
moderate disease
– Sulfasalazine (Azulfidine), 5-acetyl salicylic acid (5-
ASA
– These compounds decrease inflammation by
inhibition of cyclooxygenase and 5-lipoxygenase in
the gut mucosa.
– They require direct contact with affected mucosa for
efficacy.

• Antibiotics: used in case of fulminant colitis or
toxic megacolon
• Corticosteroids : budesonide, beclomethasone
dipropionate
– Either oral or parenteral are a key component of
treatment for an acute exacerbation of disease.
– Nonspecific inhibitors of the immune system, and
75% to 90% of patients will improve with the
administration of these drugs.
– Corticosteroid enemas provide effective local
therapy for proctitis and proctosigmoiditis

• Immunomodulating Agents
– Azathioprine and 6-mercatopurine (6-MP) are
antimetabolite drugs that interfere with nucleic acid
synthesis and thus decrease proliferation of
inflammatory cells.
– useful for treating in patients who have failed
salicylate therapy or who are dependent on, or
refractory to, corticosteroids.
– the onset of action of these drugs takes 6 to 12
weeks, and concomitant use of corticosteroids
almost always is required

• Cyclosporine is an immunosuppressive agent that
interferes with T-lymphocyte function.
• Up to 80% of patients with an acute flare of
ulcerative colitis will improve with its use.
• Improvement is generally apparent within 2
weeks of beginning cyclosporine therapy.
• Methotrexate is a folate antagonist that also has
been used to treat inflammatory bowel disease.

• Biologic Agents
– Infliximab is a monoclonal antibody directed
against TNF-α and was the first biologic agent
used to treat Crohn’s disease.
– More than 50% of patients with moderate to severe
Crohn’s disease will improve with infliximab
therapy

Ulcerative Colitis
• A dynamic disease characterized by remissions
and exacerbations.
• The clinical spectrum ranges from an inactive or
quiescent phase to low-grade active disease to
fulminant disease.
• Onset may be insidious, with minimal bloody
stools, or abrupt, with severe diarrhea and
bleeding, tenesmus, abdominal pain, and fever.

• Diagnosis is almost always made
endoscopically.
• The earliest manifestation is mucosal edema,
which results in a loss of the normal vascular
pattern.
• In more advanced disease, characteristic
findings include mucosal friability and
ulceration. Pus and mucus may also be present.

• Because the inflammation in ulcerative colitis is
purely mucosal, strictures are highly
uncommon.
• Any stricture diagnosed in a patient with
ulcerative colitis must be presumed to be
malignant until proven otherwise.
NB: In long-standing ulcerative colitis, the colon is foreshortened
and lacks haustral markings (“lead pipe”colon).

Indications for Surgery
• Emergency surgery is required for patients
with massive life-threatening hemorrhage,
toxic megacolon, or fulminant colitis who fail
to respond rapidly to medical therapy.
• Patients with signs and symptoms of fulminant
colitis should be treated aggressively with
bowel rest, hydration, broad-spectrum
antibiotics, and parenteral corticosteroids.

• Colonoscopy and barium enema are
contraindicated, and antidiarrheal agents should
be avoided.
• Deterioration in clinical condition or failure to
improve within 24 to 48 hours mandates
surgery.
• Total abdominal colectomy with end ileostomy
(with or without a mucus fistula), rather than
total proctocolectomy, is recommended.

Indications for elective surgery
• Intractability despite maximal medical therapy
• high-risk development of major complications
• In patients at significant risk of developing
colorectal carcinoma.
• Total proctocolectomy with end ileostomy has been
the “gold standard” for treating patients with
chronic ulcerative colitis.
• Restorative proctocolectomy with ileal pouch–anal
anastomosis

• The risk of malignancy increases with
pancolonic disease and the duration of
symptoms and is approximately 2% after 10
years, 8% after 20 years, and 18% after 30
years.
• Surveillance is recommended annually after 8
years in patients with pancolitis, and annually
after 15 years in patients with left-sided colitis.

Crohn’s Disease
• The presence of skip lesions is key in
differentiating Crohn’s colitis from ulcerative
colitis, and rectal sparing occurs in
approximately 40% of patients.
• The most common site of involvement of
Crohn’s disease is the terminal ileum and
cecum (ileocolic Crohn’s disease), followed
by the small bowel, and then by the colon and
rectum.

Indications for Surgery
• Surgical therapy is reserved for complications
of the disease.

Ileocolic and Small Bowel Crohn’s
Disease
• The terminal ileum and cecum are involved in
Crohn’s disease in up to 41% of patients; the
small intestine is involved in up to 35% of
patients.
• The most common indications for surgery are
internal fistula or abscess (30%–38% of
patients) and obstruction (35%–37% of
patients).

• Chronic strictures
– Short: resection
– Long or multiple fibrotic strictures: tricturoplasty
• More than 50% of patients with crohn’s will
experience a recurrence within 10 years after
resection.
• Annual surveillance colonoscopy with multiple
biopsies is recommended for patients with
longstanding Crohn’s colitis (>7 years in
duration).

Anal and Perianal Crohn’s Disease
• Anal and perianal manifestations of Crohn’s
disease are very common and occur in 35% of
all patients with Crohn’s disease.
• Isolated anal Crohn’s disease affecting only 3%
to 4% of patients.
• The most common perianal lesions in Crohn’s
disease are skin tags that are minimally
symptomatic.

• Fissures are also common. Particularly deep or
broad and perhaps better described as an anal
ulcer.
• These fissures are often multiple and located in
a lateral position rather than anterior or
posterior midline as seen in an idiopathic
fissure in ano.

• Irritable bowel syndrome is a particularly
troubling constellation of symptoms consisting
of crampy abdominal pain, bloating,
constipation, and urgent diarrhea.

INCONTINENCE
• In general, causes of incontinence can be
classified as neurogenic or anatomic.
• Neurogenic causes include diseases of the
central nervous system and spinal cord along
with pudendal nerve injury.
• Anatomic causes include congenital
abnormalities, procidentia, overflow
incontinence secondary to impaction or
neoplasm, and trauma.

• The most common traumatic cause of
incontinence is injury to the anal sphincter
during vaginal delivery.

DIVERTICULAR DISEASE
• Diverticula are actually herniations of mucosa
through the colon at sites of penetration of the
muscular wall by arterioles.
• These sites are on the mesenteric side of the
antimesenteric taeniae.
• There is often a striking hypertrophy of the
muscular layers of the colonic wall associated
with diverticulosis.

• Diverticula most commonly affect the sigmoid
colon and are confined to the sigmoid in about
half of patients with diverticulosis.
• The next most common area involved is the
descending colon (∼40% of affected
individuals), and the entire colon has
diverticula in 5% to 10% of patients with
diverticulosis.

Diverticulitis
• Diverticulitis refers to inflammation and infection
associated with a diverticulum.
• Estimated to occur in 10% to 25% of people with
diverticulosis.
• Diverticulitis is the result of a perforation of a
colonic diverticulum.
• The sigmoid colon is the segment of large bowel
with the highest incidence of diverticula, and it is
by far the most frequent site for involvement with
diverticulitis.

• Patients with diverticulitis usually complain of
left lower quadrant abdominal, pain which my
radiate to the suprapubic area, left groin, or
back.
• Abscess formation is the most common
complication of acute diverticulitis. It occurs
when the center of the inflammatory mass or
phlegmon becomes necrotic.
• The most common site for a diverticular abscess
is in the sigmoid mesocolon.

• The most common physical finding is
tenderness of the left lower abdomen. There
may be voluntary guarding of the left
abdominal musculature, and a tender mass in
the left lower abdomen is suggestive of a
phlegmon or abscess.

• Hinchey and associates described a practical
classification system that provides some
organization of the broad clinical spectrum of
the disease:
– Stage I: pericolic or mesenteric abscess
– Stage II: walled-off pelvic abscess
– Stage III: generalized purulent peritonitis
– Stage IV: generalized fecal peritonitis

Treatment
• Appropriate treatment obviously must be
individualized based on the severity of the
disease
1. Uncomplicated Diverticulitis
Uncomplicated diverticulitis (disease not
associated with free intraperitoneal perforation,
fistula formation, or obstruction) can often be
treated with antibiotics on an outpatient basis.

• Patients with uncomplicated diverticulitis
usually respond promptly to antibiotic
treatment, with marked improvement in
symptoms within 48 hours. Failure to improve
may suggest abscess formation.

• After the symptoms have subsided for at least
3 weeks, investigative studies should be
conducted to establish the presence of
diverticula and to exclude cancer, which can
mimic diverticulitis.

• The preferred test is a colonoscopic examination.
• If a patient suffers recurrent attacks of diverticulitis,
surgical treatment should be considered.
• It has generally been recommended that
sigmoidectomy be offered after two uncomplicated
attacks of diverticulitis to prevent a future
complicated episode that would require emergency
operation or a colostomy.

• Diverticulitis in the immunocompromised host
represents a special challenge for the surgeon.
Selective sigmoidectomy after a single attack
of diverticulitis should be considered in such
patients because of their diminished ability to
combat an infectious insult.

2. Complicated Diverticulitis
Abscess: Adequate drainage of the abscess,
accompanied by administration of intravenous
antibiotics, usually results in a rapid clinical
improvement.
Elective surgery should be offered after the
patient has completely recovered from the
infection, usually about 6 weeks after drainage
of the abscess.

• Small abscesses (<2 cm in diameter) may be
treated with parenteral antibiotics.
• Larger abscesses are best treated with CT-
guided percutaneous drainage and antibiotics.

• Fistula: A fistula between the sigmoid colon
and the skin (which may result from
percutaneous drainage of an abscess), bladder,
vagina, or small bowel is a relatively frequent
complication of diverticulitis.
• Such a fistula commonly forms when an abscess
is either drained or necrotizes into an adjacent
organ or onto the skin.

• Approximately 5% of patients with
complicated diverticulitis develop fistulas
between the colon and an adjacent organ.
• Colovesical fistulas are most common,
followed by colovaginal and coloenteric
fistulas.
• Colocutaneous fistulas are a rare complication
of diverticulitis.

• Diverticulitis is a more common cause of a
fistula between the colon and bladder than is
Crohn's disease or cancer.
• Sigmoid-vesical fistulas are more common in
men than women because the uterus prevents
the sigmoid from adhering to the bladder in
women.

• Symptoms of a sigmoid-vesical fistula include
pneumaturia (passage of air from the urethra
classically noted at the end of micturition),
fecaluria, and recurring urinary tract
infections.
• The most reliable test to confirm the suspicion
of a fistula between the intestine and the
bladder is a CT scan, which may demonstrate
air in the bladder

• Initial treatment of any fistula caused by
diverticulitis is to control the infection and
reduce the associated inflammation.
• Antibiotics should be administered to reduce
the adjacent cellulitis, and diagnostic steps
should be taken to confirm the cause of the
fistula before a definitive operation is
undertaken.

• Fistulas caused by diverticulitis can usually be
treated by a one-stage operation, taking down
the fistula and excising the sigmoid colon, then
fashioning an anastomosis between the
descending colon and the rectum.
• The secondary organs involved (usually the
bladder) will heal once the source of the
infection, the sigmoid colon, is removed.

• The bladder defect is usually so small that no
closure is necessary, and healing will occur if
the bladder is drained with a Foley catheter or
suprapubic cystostomy for 7 days after the
operation.

Generalized Peritonitis:
Generalized peritonitis resulting from
diverticulitis can have two causes:
(1) a diverticulum perforates into the peritoneal
cavity, and the perforation is not sealed by the
body's normal defenses, or
(2) an abscess that is initially localized expands
and suddenly bursts into the unprotected
peritoneal cavity.

• Immediate celiotomy is mandatory to identify and
excise the segment of colon containing the
perforation.
Obstruction: occurs in two circumstances. The
first is relatively unusual and is caused by
narrowing of the sigmoid due to the muscular
hypertrophy of the bowel wall.
The more common type of intestinal obstruction
is small bowel obstruction associated with the
infectious and inflammatory aspect of
diverticulitis.

Volvulus
• Volvulus occurs when an air-filled segment of
the colon twists about its mesentery.
• The sigmoid colon is involved in up to 90% of
cases, but volvulus can involve the cecum
(<20%) or transverse colon.

SIGMOID VOLVULUS
• Predisposing factors
– Long mesocolon
– Narrow attachment of pelvic mesocolon
– Band of adhesion
– Overloaded pelvic colon
• Diagnosis
– Plain radiograph shows massive colonic distension
• Management
– decompression, resection and anastomosis.

• Sigmoid volvulus produces a characteristic
bent inner tube or coffee bean appearance,
with the convexity of the loop lying in the
right upper quadrant (opposite the site of
obstruction) appearance on plain x-rays of the
abdomen.
• Gastrografin enema shows a narrowing at the
site of the volvulus and a pathognomonic
bird's beak.

ADENOCARCINOMA AND POLYPS
• Colorectal carcinoma is the most common
malignancy of the gastrointestinal tract.
• The incidence is similar in men and women and
has remained fairly constant over the past 20
years.
• Aging is the dominant risk factor for colorectal
cancer, with incidence rising steadily after age 50
years.
• More than 90% of cases diagnosed are in people
older than age 50 years.

Risk factors
• Hereditary Risk Factors
– Approximately 80% of colorectal cancers occur
sporadically, while 20% arise in patients with a known
family history of colorectal cancer.
• Environmental and Dietary Factors
– A low content of un absorbable vegetable fiber &
corresponding high content of refined carbohydrates
– A high fat content (as from meat), and
– Decreased intake of protective micronutrients such as
vitamins A, C , and E

• Inflammatory Bowel Disease
– long standing h x-↑ risk
• Polyps
– Non cancerous or precancerous growth
– Increase risk of CRC
– Common after age 50
• Other risk factors
– Obesity and sedentary life style
– Smoking
– Alcohol
– Ureterosigmodostomy
– Pelvic irradiation

Pathogenesis of Colorectal Cancer
• Adenomacarcinoma sequence
• Mutations may cause activation of oncogenes
(K-ras) and/or inactivation of tumor
suppressor genes (APC, deleted in colorectal
carcinoma [DCC], p53).
• The APC gene is a tumor suppressor gene.
Mutations in both alleles are necessary to
initiate polyp formation.

• They are now known to be present in 80% of
sporadic colorectal cancers.
• One of the most commonly involved genes in
colorectal cancer is K-ras.
• K-ras, a signaling molecule in the epidermal
growth factor receptor (EGFR) pathway, is
classified as a protooncogene because
mutation of only one allele will perturb the cell
cycle.

• When active, K-ras binds guanosine
triphosphate (GTP) hydrolysis of GTP to
guanosine diphosphate (GDP) then inactivates
the G-protein.
• Mutation of K-ras results in an inability to
hydrolyze GTP, thus leaving the G-protein
permanently in the active form.
• It is thought that this then leads to uncontrolled
cell division.

• Another common mutation occurs in the MYH
gene on chromosome 1p.
• The p53 protein appears to be crucial for
initiating apoptosis in cells with irreparable
genetic damage.
• Mutations in p53 are present in 75% of
colorectal cancers.

Genetic Pathways
• The mutations involved in colorectalcancer
pathogenesis and progression are now recognized
to accumulate via one of three major genetic
pathways:
I. The loss of heterozygosity (LOH; chromosomal
instability) pathway
II. The microsatellite instability (MSI) pathway,
and
III. The CpG island methylation (CIMP; serrated
methylated) pathway.

Colon, rectum, and anus

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