Fiser ABSITE Ch. 36-37 Colorectal/Anal Flashcards
What embryologic layer does the gut derive from?
Endoderm
In regards to for-, mid- and hindgut, what portion of the small bowel arises from each?
Forgut: Ends at the second portion of the duodenum, uses the celiac artery as blood supply. Midgut: Duodenal ampulla to first two-thirds of the transverse colon, supplied by the SMA. Hindgut: distal transverse colon and descending colon, proximal rectum, supplied by the IMA.
What is the distal rectum derived from?
The cloaca (also gives rise to the urogenital tract), with branches of the internal iliac system supplying it.
What does the anus derive from?
Invagination of the ectodermal anal pit and fusion with the distal rectum at the dentate line.
How does the longitudinal muscles of the colon and rectum differ?
It completely encapsulates the rectum, but makes of teniae coli of the colon. (which are associated with haustra).
Where is the end of the colon?
Ends at the peritoneal reflection, roughly 15 cm from the anal verge.
What is the largest diameter portion of the colon, and most prone to perforation?
The cecum, with an average diameter of 7.5 cm.
When attempting to identify the left ureter, what is a helpful landmark associated with the sigmoid colon?
The intersigmoid fossa, a small recess formed by the mesosigmoid, where it attaches to the pelvic sidewall.
At what level do the teniae coli broaden to begin the rectum?
The sacral promontory (marks the start of the rectum).
What lies just posterior to the rectum? Which layer contains lymphatics, that when dissected around, preserves them?
Presacral fascia; The fascia propria is a distinct mesothelial layer that envelops the mesorectum and presacral fascia. Dissection in the plane between the fascia propria and sacrum preserves the lymphatics contained in the mesorectum.
What ligament contains the middle rectal artery, and what are its origins?
The fascia propria condenses anterolaterally into two rectal ligamentsthat contain the middle rectal artery and mixed autonomic nerves (injury can lead to impotence and bladder dysfunction).
What region marks the beginning of the anus? What anatomic structures are found there?
The dentate line, where mucosa forms longitudinal folds (Columns of Morgagni).
In what order do the arterial branches come off the SMA?
Middle colic, then right colic and finally the ileocolic (which branches into the appendiceal artery).
What arteries supply the rectum? What are their origins?
Superior rectal - off IMA; Middle rectal - from the internal iliac artery; Inferior rectal - arises from the internal pudendal artery
What artery connects the proximal SMA and the IMA?
The Arc of Riolan.
What are the order of veins converging when creating the portal vein?
The inferior mesenteric vein joins the splenic vein, then the superior mesenteric vein joins to create the portal vein.
How does the inferior rectum’s venous drainage vary from more superior parts of the large intestine?
The distal rectum and anus are drained by the middle and inferior rectal veins into the internal iliac veins.
When ligating the IMA, what nerve injury has been described and what are its consequences?
The Hypogastric nerve, resulting in ejaculatory dysfunction in men.
What are the overall physiologic roles of the colon?
Extract water (roughly 90% recovered), sodium (90% recovered via active Na/K ATPases), short chain fatty acids (butyrate, propionate, acetate that are made by bacterial fermentation are the PRIMARY ENERGY SOURCE FOR COLONIC EPITHELIUM, also help create an osmotic gradient) and some vitamins.
In regard to bacteria, what are the most common colonic anaerobe and aerobe?
Anaerobe: Bacteroides; Aerobe: E. coli
What are the three primary contractility patterns of the colon?
Retrograde: begins at hepatic flexure down to cecum, allows increased stool mixing; Segmental contraction: short distances, further increases stool mixing; Mass movements: longer progression, with pressures rising up to 200 mmHg (highest in the sigmoid colon)
What are the two nerve complexes of the colon?
Auerbach (myenteric, located between the longitudinal and circular layers of the muscularis propria) and Meissner (submucosal, from nerve fibers that perforate the circular muscle layer).
Why are diverticula of the colon pseudodiverticula?
They only contain mucosa and submucosa, and not ALL the layers of the colonic wall.
What percentage of patients who have an episode of uncomplicated diverticulitis experience a second episode?
13%
What is Hinchey Stage I diverticulitis?
Small confined pericolic abscess (Less than 2 cm). Treated with antibiotic
What is Hinchey Stage II diverticulitis?
Larger, walled off abscess that is pericolic. Often percutaneously drained
What is Hinchey Stage III diverticulitis?
Generalized purulent peritonitis.
What is Hinchey Stage IV diverticulitis?
Generalized feculant peritonitits.
What is the most common fistula to form following complicated diverticulitis (specify for men and women)?
Men: Colovesicular fistulas, presenting with pneumaturia and recurrent UTIs.
What are the two most common causes (in order) of LARGE bowel obstruction?
Cancer if first. Benign stricture from diverticular disease is second.
How does a competent ileocecal valve change a colonic obstruction?
It creates a closed loop obstruction, leading to vascular compromise, pneumatosis and portal venous gas.
What populations are at highest risk of sigmoid volvulus?
Elderly (> 70 yo), including the debilitated and chronically constipated, and those on psychotropic medications are at highest risk. In these patients the sigmoid colon can lengthen by as much as 70%, predisposing to volvulus. On imaging they’ll have a “bent inner tube on plain film, or a whorl sign on CT.
What is the first treatment for sigmoid volvulus?
Decompression with a rectal tube placed via proctoscopy or colonoscope. Roughly 80% reduce. They will then eventually need surgical resection of the their sigmoid (nearly 20-50% will recur).
What is a cecal bascule (makes up 10% of all cecal volvulus)?
A capacious and mobile cecum flips over and is trapped by the fixed ascending colon.
What percentage of surgically reduced cecal volvulus cases will recur?
20%
At what size is colonic dilation considered an emergency due to likely vascular compromise?
12 cm.
What infectious colitis affects roughly 10% of AIDS patients?
Cytomegaloviral colitis. Treat with Gancyclovir.
What two toxins are made by C. difficile, and what overall effect do they have?
Enterotoxin A and Cytotoxin B, which cause mucosal damage, causing characteristic exudative pseudomembrane. On pathology you see PMN inflammation of mucosa and submucosa.
What are some common pathologic findings in both UC and Crohn’s disease?
Pseudopolyps (clumps of regenerating mucosa), crypt abscesses (infammatory collections in the base of the Crypts of Lieberkuhn, which contain mucus-secreting Goblet Cells).
What are some extra-intestinal manifestations of Ulcerative Colitis?
Pyoderma gangrenosum: inflammatory ulcerative skin disease often found around ostomy sites and on arms/legs. Can be controlled once intestinal disease is controlled! Primary sclerosing cholangitis: obliterating inflammatory disease of the small and large bile ducts. Colectomy does NOT improve symptoms. Arthritides, including ankylosing spondylitis and sacroiliitis, linked to UC and HLA-B27. Not improved with colectomy.
What is the overall risk of developing colorectal cancer when you have UC?
During first 10 years of disease, risk is 2-3%. It rises 2% per year after that with a lifetime risk of 35%. Therefore, annual colonoscopy starts 10 years after age of diagnosis.
What is pouchitis, a complication often seen following ileal pouch-anal anastomosis (IPAA)? Treatment?
Idiopathic inflammation of the ileal pouch, seen in 50% of patients after an IPAA. Likely due to bacterial overgrowth. Diagnosis confirmed by sigmoidoscopy. Treated with Flagyl (Metronidizole). IF the patient has stump pouchitis from unused rectum, you treat with short chain fatty acid enemas. Salycilates, stool enemas and probiotics have been shown to help.
What are indications for surgical intervention in Crohn’s disease?
1) Failure of medical therapy 2) Obstruction (from inflammation, abscess or stricture) 3) Intra-abdominal abscess 4) Symptomatic fistulas 5) Severe perianal disease 6) Failure to thrive 7) Colorectal cancer
What is sited as adequate margins when resecting Crohn’s disease?
2 cm
What are the two major types of polyps found in the colon?
Neoplastic (adenomatous) and benign (hyperplastic, juvenile, inflammatory).
What conditions do you see hyperplastic polyps (benign) in the colon?
The most common benign polyp, are usually small and have no malignant potential.
What conditions do you see juvenile polyps (benign) in the colon?
They are hamartomas, seen throughout the GI tract, often in patients with severe polyposis syndromes (aka Juvenile Polyposis syndrome, an AD disorder). Can often bleed. Not malignant, but patients at increased risk of colon cancer.
What conditions do you see inflammatory polyps (benign) in the colon?
Heaps of regenerative and inflammatory tissue, seen in BID and some erosive infections.
What are the three pathological classifications of adenomatous polyps?
Includes tubular (with branching glands, most common [75%] ), villous (with long fingerlike glands), or tubulovillous (mixed features).
What are features of adenomatous polyps are harbingers of increased risk for cancer?
Increased size (> 2 cm), villous features (40% risk), sessile appearance (flat, as opposed to pedunculated).
What constitutes and adequate polypectomy when resecting a cancerous polyp?
If malignancy is classified as 3 or below (invasion into the stalk, but NOT the submucosa of the bowel wall), is well or moderately differentiated, and margins are > 2 mm. These patients then require early repeat colonoscopy at 3 years out due to 40% risk of developing another cancerous polyp.
Why are polyps classified as a Level 4 (invading colonic submucosa), or with poorly differentiated lesions, not adequately treated by polypectomy?
Because risk of nodal metastasis is 10%, and therefore requires surgical resection.
What is the most common mutation in Familial Adenomatous Polyposis (FAP)?
Most often (80% of the time) due to autosomal dominant APC mutation (a tumor suppressor gene) on chromosome 5. * Remember, that there is a 100% chance of developing cancer by 40 y/o! These patients get total colectomies prophylactically at 20 years old (total abdominal colectomy with IPAA)
What is Gardner Syndrome?
Genetic disorder causing GI polyposis, ostemoas, sarcomas and epidermoid inclusion cysts.
