Colon Diseases

Published on 16/04/2015 by admin

Filed under Surgery

Last modified 22/04/2025

Print this page

rate 1 star rate 2 star rate 3 star rate 4 star rate 5 star
Your rating: none, Average: 0 (0 votes)

This article have been viewed 2968 times

9 Colon Diseases

Anatomy of the Colon

image

Viscera: Mucosa and Musculature of Large Intestine

Parts and Landmarks

• Cecum, appendix, and ascending, transverse, descending, and sigmoid colon ~150 cm total length
• Cecum has the largest diameter: with obstruction, this is the most likely location for a perforation (greatest increase in pressure, per Laplace’s law).
• Colon externally distinguished by omental (epiploic) appendices, haustra (sacculations), and taeniae coli (triple bands of longitudinal smooth muscle)
• Only transverse and sigmoid portions typically have mesenteries.
• Greater omentum is fused to the transverse mesocolon and may be carefully separated surgically.
• Inferior ascending colon can have a mesentery (~10%) and is very mobile (risk for volvulus).
• See also appendix and anorectal topics.

Microscopic Anatomy

• Mucosa

image Epithelium: enterocytes (absorptive), goblet cells
image Lamina propria
image Muscularis mucosa

• Submucosa: strongest layer (connective tissue); Meissner’s plexus (neuronal network)
• Muscularis

image Auerbach’s plexus: myenteric neurons
image Inner circular muscle
image Outer longitudinal layer reduced to 3 bands: taeniae coli

image Mesocolic: posterior, attached to sigmoid and transverse mesocolon
image Omental: to which the epiploic appendages (appendices) are attached
image Free: with no omental or mesenteric attachments
image The taeniae merge into a continuous layer in the appendix and the rectum.

• Serosa: peritoneum
• Haustra: sacculations of the wall between the taeniae

Embryology

• From the cecum to the splenic flexure of the transverse colon, the colon was derived from the caudal midgut and is supplied by the superior mesenteric artery and vagus.
• From the descending colon through rectum, the colon was derived from hindgut and is supplied by the inferior mesenteric artery and sacral parasympathetics.

Innervation

Parasympathetic

• Preganglionic fibers

image Vagus: innervate colon from ileocecal junction to splenic flexure
image Pelvic splanchnic nerves (S2-S4): innervate descending and sigmoid colon

• Postganglionic fibers

image Meissner’s plexus: inner submucosal layer contains parasympathetic ganglion cells
image Auerbach’s plexus: outer, myenteric, contains parasympathetic ganglion cells

Sympathetic

• Preganglionic fibers distributed via splanchnic nerves to superior and inferior mesenteric plexuses
• Postganglionic fibers from cells in the following

image Superior mesenteric ganglion to the ascending and transverse colon via superior mesenteric plexus
image Inferior mesenteric ganglion to the descending and sigmoid colon via inferior mesenteric plexus

Sensory Fibers

• Vagal afferents from ascending and transverse colon
• Segmental visceral afferents for ascending and transverse colon travel parallel to sympathetics through the superior mesenteric plexuses and splanchnic nerves.
• Descending and sigmoid colon send visceral afferents through the inferior mesenteric, hypogastric, and pelvic plexuses.

Vessels and Lymphatics

image

Arteries of Large Intestine

Arterial Supply

• Superior mesenteric artery branches

image Ileocolic artery (with appendicular branch)
image Right colic artery
image Middle colic artery

• Inferior mesenteric artery branches

image Left colic artery (retroperitoneal)
image Sigmoid arteries (3 or 4)
image Superior rectal artery

• Marginal artery anastomoses between the superior and inferior mesenteric arteries
• Internal iliac artery branches

image Middle rectal artery
image Inferior rectal artery

• Rectal arteries anastomose: inferior mesenteric to internal iliac branches
image

Veins of Large Intestine

Venous Drainage

• Superior mesenteric vein (right portal vein tributaries)

image Ileocolic vein (with appendicular branch)
image Right colic vein
image Middle colic vein

• Inferior mesenteric vein (drains into splenic: left portal vein tributaries)

image Left colic veins
image Sigmoid veins
image Rectosigmoid veins
image Superior rectal veins

• Internal iliac veins (inferior vena cava tributaries)

image Middle rectal veins
image Inferior rectal veins

• Rectal veins anastomose in “hemorrhoidal plexus” of rectum, the site of portocaval shunting and hemorrhoids in portal hypertension (see also anorectal topics, Chapter 16).
image

Lymph Vessels and Node of Large Intestine

Lymphatic Drainage

• Parallels the arterial supply
• Right-sided mucosal and epicolic nodes drain along superior mesenteric branches into superior mesenteric nodes.
• Left-sided nodes drain along inferior mesenteric artery branches into inferior mesenteric and lateral aortic nodes.
• Deeper drainage superiorly into nodes along aorta and into the cisterna chyli

Clinical Correlates

Diverticula

• True (congenital) diverticulum: consists of entire gut wall, not usually seen in colon (e.g., Meckel’s diverticulum [in terminal ileum])
• False (acquired) diverticulum: mucosa protruding through muscle wall, typical of colon
• Acquired diverticula usually occur adjacent to taeniae coli, where nutrient arteries penetrate the bowel wall.
image

Diverticulosis of Colon

Diverticulosis

• Incidence: 5%-10% of persons older than 45 years, 50%-60% by age 60 years, approaching 80% by 80 years
• 80%-90% of diverticula seen in sigmoid colon
• Cause thought to be increased intraluminal pressure owing to slowed fecal transit
• High-fat, low-fiber diets a contributing factor
• About 3 times more likely in men
• About 20% of cases in persons younger than 50 years
• Much less prevalent currently in less industrialized societies
• Visualized with abdominal CT

Diverticulitis

• Inflamed diverticula and/or perforation, assumes diverticulosis
• Usually manifests with fever and left lower quadrant pain
• Diffuse abdominal pain can indicate perforation.
• A very redundant sigmoid can produce symptoms in any quadrant.
• Constipation, nausea, and vomiting can occur.
• Occurs in 5%-10% of patients with diverticulosis, over a 5-year period
• Occurrence increases to 35% over 20 years.

Polyps

• Categories: nonmalignant, premalignant, malignant
• Sessile: flat
• Pedunculated: stalked
• Juvenile polyps

image In patients younger than 10 years
image Typically nonmalignant hamartomas

• Adenomas

image Benign, premalignant
image Types: tubular, villous, or mixed
image Peak incidence at ~50 years

image

Colorectal Cancer

Cancer

• Colorectal cancer: diagnosed in ~130,000 Americans per year
• Adenocarcinoma most common type

image Ulcerative: most common, central depression with raised edges
image Polypoid: large, as described for polyps
image Annular: apple core appearance on contrast study, associated with obstruction
image Diffusely infiltrating:

image Thickening of bowel wall
image May be flat
image Difficult to diagnose

Colitis (by Type)

• Amebic colitis

image Site of primary infection by Entamoeba histolytica
image Risk factors include travel in Mexico, alcohol ingestion

• Ischemic colitis: caused by low flow state or inferior mesenteric ligation
• Pseudomembranous colitis

image Caused by Clostridium difficile infection
image Can occur after antibiotic treatment

image

Crohn’s Disease

• Crohn’s disease

image Idiopathic inflammatory bowel disease, usually involving small and large intestine, but lesions can occur in GI tract from mouth to anus
image Higher rate of occurrence in Ashkenazi Jews
image Terminal ileum is the most commonly involved segment.
image Asymmetrical distribution of lesions
image Discrete (aphthous) and longitudinal ulcers common
image Gross bleeding may be absent (25%-30%).
image Rectum often spared (~50%)
image Perianal disease ~75%
image Fistulization
image Granulomas 5%-75%
image Discontinuous mucosa involvement
image Mucosal friability uncommon
image Relatively normal surrounding mucosa
image Cobblestoning in severe cases
image Normal vascular pattern
image Surgery not curative (unlike ulcerative colitis)

image

Ulcerative Colitis

• Ulcerative colitis

image Restricted to colon
image Continuous distribution of lesions starting distally
image Rectum involvement ~90%
image Gross bleeding
image Perianal disease rare but may be severe
image No fistulization
image No granulomas
image Contiguous mucosa involvement
image Discrete (aphthous) and longitudinal ulcers rare
image Abnormal surrounding mucosa
image No cobblestoning
image Rectal involvement ~90% of cases
image Mucosal friability common
image Distorted vascular pattern

Large Bowel Obstruction

• Cancer and diverticular disease: most common causes of bowel obstruction in the U.S.
• Volvulus: rare cause of obstruction in the U.S. but most common cause in third world countries (associated with extra-high dietary fiber intake)

Volvulus

• Twisting of the bowel, causing a blind loop with obstructions at both ends (Latin volvere, “to twist, to turn”)
• More common in sigmoid colon (with redundancy and mesentery) and cecum
• In ~11%: very mobile ascending colon with mesentery, predisposing to volvulus
• Midgut volvulus can occur in pediatric patients with malrotations.

Aspects of Colectomy (Below)

image

Surgical Resection of Colon Cancer

Related posts:

Skull and Face Fractures Anorectal Diseases Uterus and Adnexal Diseases Thyroid Diseases Pelvic Fractures Ribs and Thorax Fractures