Colon Flashcards
Function of the colon
reabsorption of water and sodium
secretion of potassium and bicarb
storage of feces
Is the colon retroperitoneal or intraperitoneal?
Ascending and descending colon are fixed retroperitoneally
Transverse colon is intraperitoneal
Sigmoid is also intraperitoneal
What part of the colon does the SMA supply (and what are the branches of the SMA that supply it)?
The SMA gives off the ileocolic, right colic, and middle colic arteries. These supply the cecum, ascending, and proximal to mid-transverse colon.
What part of the colon does the IMA supply (and what are the branches of the IMA that supply it)?
IMA gives off left colic, sigmoid, and superior hemorrhoidal arteries. This supplies the mid-transverse colon to the rectum. This area is also supplied by the middle and inferior hemorrhoidal arteries, which don’t come from the IMA- they come from the internal iliac.
What is the long anastamoses between the SMA and IMA?
anastomosis of Riolan
What are the arcades that are close to the mesenteric border of the colon called?
The marginal artery (of Drummond)
What is the venous drainage of the colon?
SMV and IMV.
IMV joins the splenic vein. The splenic vein joins the SMV and together they form the portal vein. So, mesenteric blood flow goes to the liver- it’s detoxed before it goes back to the central circulation
What is ulcerative colitis? Where does it occur?
Inflammation of the colon, starting from rectum and going retrograde. Inflam is confined to mucosa and submucosa only.
What human leukocyte antigens are a/w ulcerative colitis?
HLA-AW24 and HLA-BW25
Px of UC
bloody diarrhea, fever, abd pain, weight loss.
If abd distention (d/t massive colonic distention), it’s toxic megacolon, which can progress to perforation, peritonitis.
Dx eval for UC
Colonscopy- shows thickened, friable mucosa. Also fissures and pseudopolyps.
Biopsy- ulceration limited to mucosa and submucosa.
Barium enema- “stovepipe colon” w smooth edges and ulcers
Complications in UC
Perforation Obstruction Hemorrhage Toxic megacolon Colon cancer (10%)
Rx for UC
Medical Rx- steroids, immunosuppressants, Sulfasalazine. Topical mesalamine (enema) for mild/moderate
Also fluids, electrolytes, TPN if needed
Infliximab monoclonal Ab against TNF
Later surgery if indicated
What are the indications for surgery in UC?
colonic obstruction massive blood loss failure of medical Rx toxic megacolon cancer
What is diverticulosis?
Diverticula- outpouching of colonic wall
Occurs at points where arterial supply penetrates the bowel wall.
Acutally false diverticula, bc not all layers of bowel wall are included
Where do most diverticula occur?
Sigmoid colon
What is the most common cause of lower GI hemorrhage?
Diverticulosis- usu from R colon
Pt px of diverticulosis
Bleeding from rectum but no other complaints.
Maybe had previous bleeding/crampy abd pain in LLQ
Dx eval for diverticulosis
If bleeding stopped spontaneously- do a colonoscopy to determine etiology.
If bleeding is continuous- do radioisotope bleeding scan (ok) or mesenteric angiography (best)
Rx for diverticulosis
If asx- no Rx. 80% stop spontaneously.
If recurrent bleeding- surgical resection
If active bleeding- rx via colonoscopy- embolize bleeding vessel w angiography.
if all else fails- emergent subtotal colectomy (remv most of the colon)
if bleeding site id’d- segmental colectomy of that part.
What is diverticulitis?
Infection of diverticula. Narrow neck –> increased intraluminal prs or inspissated food particles.
Infection –> localized or free perforation into the abd.
Where does diverticulitis most commonly occur?
Sigmoid colon
Px of diverticulitis
LLQ pain, abd tenderness.
local peritoneal signs- rebound, guarding.
if diffuse peritoneal signs, it’s free intra-abd perforation :(
Dx Eval of diverticulitis
Blood- WBC count high
XR- normal
CT- shows percolic fat stranding, bowel wall thickening, or abscess
Do NOT do colonoscopy or barium enema- can cause/worsen perforation
Complications of diverticulitis
stricture
perforation
fistula w bladder, skin, vag, other part of bowel
Rx for diverticulitis
Most are mild- oral abx outpatient: cipro and metronidazole to cover bowel flora
Severe cases- hospitalize w bowel rest and IV abx- ampicillin, levofloxacin, metronidazole
if no improvement- CT drainage
If perforation, surgical drainage + colostomy
If complications or multiple attacks- surgical resection
How does colon cancer start out?
Adenomatous polyp which undergoes malignant transformation.
What genes are a/w colon ca?
50% have Ras gene mutation
75% have p53 gene mutation
What are the classifications of adenomatous polyps?
Tubular and villous (some lesions have characteristics of both)
Villous = bad. Higher villous component = higher malignancy.
Size also matters - bigger size - more malignant.
What type of cancer is colon cancer?
90% are adenocarcinoma
and 20% of those are mucinous- worst pgx.
Other types: squamous, adenosquamous, lymphoma, sarcoma, carcinoid
Screening for colon ca?
Start at 50, 40 if increased risk.
Yearly fecal-occult blood test
Sigmoidoscopy every 3-5 yrs
Colonoscopy or barium enema every 10 years
Px of colon ca
Occult blood in stool can be only sign.
R colon lesions- bleeding
L colon lesions- obstructive sx, chg in stool caliber, tenesmus (feel like constantly need to pass stool), constipation
Constitutional- weight loss, anorexia, fatigue
Dx eval for colon ca
Hematocrit- shows anemia CEA- good for measuring recurrence LFTs abn if liver mets Barium enema- can show malignancy Colonoscopy- can biopsy/excise lesion CT- look for extent of dz, mets PET- mets, esp if CEA indicates recurrence If rectal lesions- endorectal US
Rx for colon ca
Surgical removal of lesion.
If endoscopic removal + path report says carcinoma in situ with complete excision- that’s all.
If can’t be remvd endoscopically- bowel resection
If lesions close to anus- colostomy
What is the most common site for colon ca mets?
The liver
Which has less morbidity, open or laparoscopic removal for colon resection?
Lap
What chemo is used for colon ca?
5FU and levamisole
Describe colectomy op
Pre-op mechanical and antimicrobial cleanse.
Midline incision
To mobilize R or L colon, must incise R or L white line of Toldt
Avoid ureter- use ureteral stent if necessary.
After colon mobilization, incise peritoneum over the mesentery to its root, ligate all mesenteric vessels.
Anastamose.
What is the px of angiodysplasia?
Multiple episodes of low-grade lower GI bleeding.
10% have massive bleeding
Common in elderly
Dx eval of angiodysplasia
arterography
nuclear scans
colonscopy
Rx for angiodysplasia
Endoscopy w laser ablation
electrocoagulation
angiography w vasopressin
but 80% of lesions re-bleed, so definitive Rx (segmental colonoscopy) is usu recommended.
What is volvulus?
Part of colon rotates on its mesentery, obstructing blood flow and creating closed-loop obstruction
Most common locations for volvulus?
Sigmoid (75%)
Cecum (25%)
Risk factors for volvulus
Age
Chronic constipation
Prev abd surgery
Neuropsychiatric disorders
Pt px for volvulus
acute onset crampy abd pain and distention.
tender, distended abd, peritoneal signs- rebound, guarding
Can turn into frank peritonitis, shock
Dx eval for volvulus
Abd XR- massively distended colon and “bird’s beak” at the point of obstruction
Rx for volvulus
Sigmoid volv- reduce via rectal tube, enema, or proctoscopy. But often recurs, so after you fix it, operate.
Cecal volv- operate immed bc can’t really fix it
Most coomon reason for urgent abd operation
Appendicitis
Px of appendicitis
Epigastric pain that migrates to RLQ Anorexia! RLQ tenderness, McBurney's point Rebound, guarding Low fever if high fever- perforation
Signs of peritoneal irritation in appendicitis
obturator sign- pain on external rotation of flexed thigh
psoas sign- pain on right thigh extension
Where is McBurney’s point?
between umbilicus and ASIS (anterior superior iliac spine)
Dx eval for appendicitis
WBC mildly elevated
US- wall thickening, luminal distention, lack of compressibility (also good to r/o ovarian path in women)
Barium enema- shows non-filling of appendix
CT shows inflam
Rx for appendicitis
Appendectomy- either open or lap
If appendiceal abscess w clinical improvement- can have abx and CT-guided drainage
Kids w perforation- appendectomy w drainage of abscess
