22 - Colon, Rectum, Anus

Taenia coli

The colon is characterized by three bands of longitudinal muscle called:

Cecum

Which segment of the colon is the widest and hence the least likely to obstruct?

Cecum

Which segment of the colon has the thinnest wall and is the most common site of perforation?

Sigmoid colon

Which segment of the colon is the narrowest and hence is the most common site of obstruction?

Sigmoid colon

Also the most common site of diverticulosis and diverticulitis

Which segment of the colon is the most common site of volvulus?

Middle colic (1st branch)

Right colic (2nd branch)

Ileocolic (3rdbranch)

The branches of the superior mesenteric artery supplying the colon are:

Marginal artery of Drummond

This artery represents the anastomoses between the terminal branches of the superior mesenteric artery and the inferior mesenteric artery

Short chain fatty acids (acetate, propionate, butyrate)

The colon uses these molecules as fuel:

Nervi erigentes

The pelvic splanchnic nerves provide parasympathetic supply to the distal colon. They arise from S2-S4 and are also called:

Volvulus

Omega sign and coffee bean sign on abdominal radiography are pathognomonic signs for:

Cecal volvulus

Abdominal radiography shows a kidney-shaped air-filled structure in the left upper quadrant

___ volvulus is more common in younger patients and represents 20% of colonic volvulus

False diverticulum

A ____ diverticulum lacks a portion of normal bowel wall

Lack of dietary fiber

What is the main etiology of diverticular disease?

Abdominal CT scan with IV Contrast

What is the best diagnostic for the diagnosis of diverticulitis?

Clear liquid diet and broad spectrum antibiotics, then high fiber diet

What is the management of uncomplicated diverticulitis?

Distal to the ligament of Treitz

Lower gastrointestinal bleeding is defined by bleeding distal to this anatomic landmark:

Left side

LGIB from the ___ side of the colon can manifest as hematochezia (bright red blood per rectum)

Infectious colitis

In a young patient with fever, abdominal cramps, and hematochezia, the primary differential for LGIB is:

Diverticular bleeding

In an elderly patient with acute painless bleeding and no other symptoms, the primary differential for LGIB is:

Slow and recurrent

Angiodysplasia is a painless, self-limited LGIB that is characterized as ____ in contrast to diverticular bleeding

Insertion of nasogastric tube (NGT) with aspiration/lavage

Brisk UGIB can often mimic LGIB. Hence, this can be performed to determine the presence of blood proximal to the ligament of Treitz

Colonoscopy

What is the test of choice to identify the site of lower GI bleeding?

99mTc-labeled RBC scintigraphy

This technique allows for continuous monitoring which can detect bleeding that angiography or colonoscopy can miss

This nuclear medicine test is highly sensitive for active bleeding and obscure GI bleeding as it can detect bleeding rate as little as 0.1 mL/min

Upper endoscopy (EGD) to rule out UGIB

In the setting of hematochezia with hemodynamic instability, urgent ____ is warranted

0.5 mL/min

Angiography can detect a bleeding rate of at least ___ mL/min

Protective factor

Yosi = UC

Smoking is considered a ____ factor in ulcerative colitis

Ulcerative colitis

UC vs Crohn’s: involves the rectum and has continuous distribution throughout the colon

Ulcerative colitis

UC vs Crohn’s: limited to the mucosa and superficial submucosa

Ulcerative colitis

UC vs Crohn’s: total proctocolectomy can be curative

Crohn’s disease

UC vs Crohn’s: affects any part of the GIT from the mouth to the anus

Crohn’s disease

UC vs Crohn’s: rectum is often spared or normal; associated with skip lesions

Crohn’s disease

UC vs Crohn’s: characterized by “cobblestone” appearance on endoscopy

Crohn’s disease

UC vs Crohn’s: associated with fistulas due to transmural involvement

Serrated type

The CpG island methylation pathway is observed in ____ type of colonic polyps

Rectosigmoid

Most colorectal polyps are found in the ___ area of the colon

Hyperplastic polyps

What is the most common histologic type of colonic polyp?

Peutz-Jeghers syndrome

Hamartomatous polyps are not premalignant unless when associated with:

Yes

Are serrated polyps considered premalignant?

Villous > tubulovillous > tubular

Villous is villainous

Among tubular, tubulovillous, and villous types of adenomatous polyps, arrange in order of risk of cancer:

Pedunculated

Haggitt classification is used to classify the extent of invasion of ____ malignant colonic polyps

Sessile

Kikuchi classification is used to classify ____ malignant colonic polyps

APC gene on chr 5q21

Familial adenomatous polyposis is associated with a defect in what gene?

Gardner syndrome

This polyposis syndrome associated with FAP is also associated with epidermoid cysts, osteomas of the skull, and desmoid tumors of the abdominal wall

Turcot syndrome

Turcot = turban on the head, CNS tumors

This polyposis syndrome similar to FAP is associated with CNS tumors

Juvenile polyposis syndrome

What is the most common hamartomatous polyposis syndrome?

Peutz-Jeghers syndrome

What is the second most common hamartomatous polyposis syndrome?

Peutz-Jeghers syndrome

This hamartomatous polyposis syndrome is additionally characterized by mucocutaneous hyperpigmentation (perioral, buccal, occasionally genital)

MLH1, MSH2

Which DNA mismatch repair genes are linked to HNPCC (Lynch syndrome)?

At least 3 relatives must have histologically verified colorectal cancer

At least 2 successive generations must be affected

1 must be the first-degree relative of the other 2

At least 1 diagnosed before age 50

*FAP should be excluded

What is the 3-2-1 rule for the diagnosis of HNPCC (Amsterdam criteria)?

Right-sided

____-sided colon cancer is associated with occult bleeding, anemia, postprandial discomfort, weakness

Left-sided

____-sided colon cancer is associated with changes in bowel habits, alternating diarrhea and constipation, and hematochezia

45

The ACS recommends screening for colon cancer beginning at age ___

10 years

Screening for colon cancer can be performed with colonoscopy every ___ years

FOBT or FIT every year

Flexible sigmoidoscopy every 5 years

Screening for colon cancer can be performed with FOBT or FIT every ___ and flexible sigmoidoscopy every ___

Treatment monitoring

Rise in CEA after surgical treatment signals recurrence of the tumor

What is the main clinical utility of CEA testing in colon cancer?

12 lymph nodes

What is the minimum adequate lymph node harvest in the surgical management of colon cancer?

Ileocolic artery

Right colic artery

Right branch of middle colic artery

In a right hemicolectomy, what arteries are ligated?

Inferior mesenteric artery

Left colic artery

In a left hemicolectomy, what arteries are ligated?

5 cm

What is the adequate margin of resection in colon cancer?

2 cm

What is the adequate margin of resection in rectal cancer?

Metachronous: second cancer diagnosed >6 months after primary

Synchronous:second cancer diagnosed within 6 months after primary

Differentiate metachronous versus synchronous cancers

Neostigmine

IV neostigmine 2mg is extremely effective. Must rule out mechanical obstruction

Drug of choice for the treatment of Ogilvie syndrome

Pseudomembranous colitis

What is the leading cause of nosocomial acquired diarrhea?

Clostridium difficile

Pseudomembranous colitis is caused by?

Upper 2/3

Which part of the rectum is covered by peritoneum?

Dentate line

This anatomic landmark refers to the transition from the columnar rectal mucosa to the squamous anoderm

Dentate line to anal verge

The anatomic anal canal extends from ____ to ____

Anorectal junction to anal verge

The surgical anal canal extends from ____ to ____

Pubococcygeus

Iliococcygeus

Puborectalis

The levator ani muscle supports the pelvic viscera. It is composed of which muscles?

Denonvilliers’ fascia

This fascia separates the anterior rectum from the vagina in females, and the prostate and seminal vesicles in males

Mesorectum

Removed during TME: total mesorectal excision

TME is correlated with lower recurrence and higher survival in patients with rectal cancer

This layer of fatty connective tissue surrounds the rectum and contains its vessels and lymph nodes. Removed during rectal cancer surgery

Altemeier procedure

This procedure to treat rectal prolapse in elderly high-risk patients involves perineal rectosigmoidectomy, also known as?

Left lateral (3 o’clock)

Right anterior (11 o’clock)

Right posterior (7 o’clock)

What are the main hemorrhoidal cushions and where are they located?

Sliding anal cushion theory

According to this theory of hemorrhoid pathophysiology, repeated stretching causes fragmentation of the submucosal muscle of Treitz, which anchors and suspends the anal lining

Internal hemorrhoids

___ hemorrhoids are located above the dentate line and present with painless bright red bleeding

External hemorrhoids

___ hemorrhoids are located below the dentate line and present with itching and pain

Grade II

What grade of hemorrhoids protrudes beyond the anal verge but spontaneously reduces?

Grade III

What grade of hemorrhoids protrudes beyond the anal verge but requires manual reduction?

Grade III

Hemorrhoids grade ___ and above are managed surgically

Warm sitz bath

What is the most effective topical treatment for the relief of symptoms of hemorrhoids?

Hard stools, prolonged diarrhea

What is the main etiology or cause of anal fissures?

Lateral internal sphincterotomy

Indicated for anal fissures that have failed medical management

Chronic anal fissures are managed surgically with this procedure:

Obstetric injuries

50% of fistulas caused by obstetric injury heal spontaneously: wait 3 to 6 months before surgical repair

What is the most common cause of rectovaginal fistulas?

Direct/radial route or straight line to the anus

According to Goodsall's rule, what is the course of the fistula if the external opening is located anterior to the transverse line ≤ 3 cm from the anus?

Curved path to the posterior midline

According to Goodsall's rule, what is the course of the fistula if the external opening is located posterior to the transverse line?

Curved path to the posterior midline

This is the exception to Goodsall’s rule

According to Goodsall's rule, what is the course of the fistula if the external opening is located anterior to the transverse line more than 3 cm from the anus?

≥30 percent

Complex anal fistulas include high trans-sphincteric fistulas that encompass more than ___ percent of the external sphincter

Continence

The goal is to obliterate the fistula tract while preserving anal sphincter function

The treatment goal in the management of fistula-in-ano is the eradication of sepsis without sacrificing ____

Anal bleeding

What is the most common symptom of anal carcinoma?

Squamous cell carcinoma

What is the most common carcinoma of the anus?

Nigro protocol (5-fluorouracil, mitomycin C, and radiotherapy)

What is the standard treatment for the management of anal canal squamous cell carcinoma?

5-fluorouracil

Mitomycin C

Radiotherapy

Chemoradiation often serves as the definitive treatment for anal cancer, and allows for sphincter preservation and avoids permanent end colostomy. Surgery is reserved for lesions <1cm and well-differentiated

What are the components of the Nigro protocol for the management of anal cancer?

Low anterior resection (LAR)

This surgical procedure is used to treat cancer of the middle and the upper third of the rectum and is an anal-sparing procedure

Abdominoperineal resection (APR)

APR is performed when complete tumor removal requires sacrifice of the anal sphincter complex, necessitating a permanent colostomy

This surgical procedure involves resection of part of the sigmoid colon, rectum, and anus and the construction of a permanent end colostomy. Indicated when the levator ani or sphincter are involved

Transition zone

Seen between distal nondilated bowel and proximal dilated bowel

What is the characteristic finding of Hirschsprung disease as seen on barium enema?

Levator ani muscle

Imperforate anus is categorized into high or low based on what landmark?