Large Bowel, Mesentery and Peritoneum Flashcards
Overview of Colitis
What is it?
Primary imaging findings?
What is included in a full clinical evaluation?
How often is incidental colonic wall thickening found incidentally on CT scan?
- Colitis is inflammation of the colon that may be caused by several unrelated etiologies, often with overlapping imaging findings.
- The primary imaging feature of colitis is bowel wall thickening. Generally, a full clinical evaluation, stool studies, and sometimes colonic biopsy are required for a definitive diagnosis.
- Incidental colonic wall thickening is found in as many as 10% of CT scans.
Ischemic Colitis
Causes?
What part of the large bowel is particularly susceptible?
What part is particularly resistant? Why?
What is a suggestive CT finding?
If arterial thromboembolic dz suspected, what should be evaluated?
If chronic arterial stenosis is suspected, what should be evaluated?
- Colonic ischemia can be caused by acute arterial thrombus, chronic arterial stenosis, low-flow states (e.g., congestive heart failure), and venous thrombosis.
- The splenic flexure is the watershed region between the superior and inferior mesenteric arteries and is especially susceptible to ischemia in low-flow states.
- The rectum is supplied by a dual blood supply and is almost never affected by ischemia. The superior rectal artery (terminal branch of the IMA) and the inferior and middle rectal arteries (arising from the internal iliac artery anterior division) form perirectal collaterals.
- A suggestive CT finding of ischemic colitis is segmental, continuous thickening of the affected colon in a vascular distribution, with sparing of the rectum
- If arterial thromboembolic disease is suspected, one should evaluate for the presence of aortic atherosclerotic disease or a left atrial thrombus in the setting of atrial fibrillation.
- If chronic arterial stenosis is suspected, one should evaluate for atherosclerosis of the mesenteric vessels.
Infectious Colitis
What are the possible etiologies?
General imaging appearance?
Specific image pattern of: Yersinia, Salmonella, Tuberculosis, E. coli, and CMV, C. diff?
- Infectious colitis can be bacterial, tubercular, viral, or amoebic. There is a large overlap in the clinical presentation and imaging findings of the various pathogens.
- In general, infectious colitis features pericolonic stranding and ascites in addition to the colonic wall thickening seen in all forms of colitis.
- Yersinia, Salmonella, and colonic tuberculosis affect the right colon. Tuberculosis is known to involve the ileocecal valve, resulting in a desmoplastic reaction that mimics Crohn disease.
- E. coli, CMV, and C. diffcile colitis most commonly cause pancolitis.
Pseudomembranous Colitis
What is it? Most commonly due to what? Who else can it occur in?
Key imaging finding?
What is “accordian” sign?
What is “thumbprinting”?
- Pseudomembranous colitis is an especially prevalent form of infectious colitis caused by the overgrowth of Clostridium difficile, most commonly due to alteration in colonic bacterial flora after antibiotic use. Pseudomembranous colitis may also occur without a history of antibiotics, especially in hospitalized or nursing home patients.
- A key imaging finding is marked thickening of the colonic wall, typically with the involvement of the entire colon (pancolitis). The accordion sign describes severe colonic wall thickening combined with undulation of enhancing inner mucosa. It signifies severe colonic edema but is not specific to C. diffcile. Thumbprinting is a fluoroscopic finding of thickened haustra and is also due to edema.
Ulcerative Colitis
What is it?
In what scenario would the rectum appear normal relative to the rest of the colon?
UC patients have an increased risk of what?
What are the extra-abdominal manifestations of UC?
In what scenario can UC mimick Crohns on imaging?
What is a “collar-button” ulcer?
What are chronic changes of UC?
- Ulcerative colitis is an idiopathic inflammatory bowel disease that begins distally in the rectum and spreads proximally in a continual manner (unlike Crohn disease, which features skip areas).
- Of note, it is possible for the rectum to appear normal with more proximal colonic involvement present if the patient has been treated with corticosteroid enemas.
- Patients with UC have an increased risk of primary sclerosing cholangitis, colon cancer, and cholangiocarcinoma.
- Extra-abdominal manifestations of UC include sacroiliitis, iritis, erythema nodosum (tender red subcutaneous nodules), and pyoderma gangrenosum (cutaneous ulcers).
- UC does not extend more proximally than the cecum; however, a backlash ileitis caused by reflux of inflammatory debris into the ileum may mimic Crohn disease.
- Imaging of ulcerative colitis features circumferential wall thickening with a granular mucosal pattern that is best seen on barium enema. Pseudopolyps may be present during acute inflammation, representing islands of normal mucosa surrounded by inflamed mucosa. A collar-button ulcer is nonspecific but represents mucosal ulceration undermined by submucosal extension.
- Chronic changes of ulcerative colitis include a featureless and foreshortened lead pipe colon. Similar to Crohn disease, fat-attenuation of the colonic wall suggests chronic disease, as seen in this case attached.
What is the more severe complication of ulcerative colitis?
What causes this complication?
Imaging criteria?
What is contraindicated during this complication?
- Toxic megacolon is a severe complication of ulcerative colitis (and less commonly, Crohn disease) caused by inflammation extending through the muscular layer.
- Imaging of toxic megacolon shows dilation of the colon to greater than 6 cm in association with an adynamic ileus. Colonic perforation may occur and colonoscopy is contraindicated in suspected toxic megacolon.
Typhlitis
What is it?
Seen in what population?
Treatment?
- Typhlitis = neutropenic enterocolitis
- Typhlitis is a right-sided colitis seen in immunocompromised patients.
- Treatment is with broad-spectrum antibiotics and antifungals.
Familial Adenomatous Polyposis (FAP)
What is it?
Treatment?
There are polyps in what other location?
What are the two variants?
- Familial adenomatous polyposis FAP is an autosomal-dominant syndrome featuring innumerable premalignant adenomatous polyps in the colon and to a lesser extent the small bowel. Prophylactic colectomy is the standard of care to prevent colon cancer.
- Gastric polyps are also present, although the gastric polyps are hyperplastic and are not premalignant.
- Gardner syndrome is a variant of FAP. In addition to colon polyps, patients also have (DOPE - since the “Gardner grows DOPE”):
- Desmoid tumors
- Osteomas
- Papillary thyroid cancer
- Epidermoid cysts
- Turcot syndrome is another variant of FAP. In addition to colon polyps, patients also
have CNS tumors (gliomas and medulloblastomas).
* Mnemonic: "TURBan" is on the head ie CNS
Hereditary nonpolyposis colon cancer syndrome (HNPCC) = Lynch syndrome
What is it? What is the cause?
What kind of polyps?
What else is HNPCC associated with?
- Hereditary nonpolyposis colon cancer HNPCC syndrome (also called Lynch syndrome) is an autosomal dominant polyposis syndrome caused by DNA mismatch repair, leading to colon cancer from microsatellite instability on a molecular level.
- Similar to FAP, the colon polyps of HNPCC are adenomatous.
- HNPCC is associated with other cancers, including endometrial, stomach, small bowel, liver, and biliary malignancies.
Peutz-Jeghers
What is it?
What do these pedunculated polyps lead to (mechanically)?
Characteristic skin manifestations?
Associated with what other neoplasms?
- Peutz-Jeghers is an autosomal dominant syndrome that features multiple hamartomatous pedunculated polyps, usually in the small bowel. These polyps may act as lead points and cause intussusception.
- Characteristic skin manifestations include perioral mucocutaneous blue/brown pigmented spots on the lips and gums.
- Peutz-Jeghers is associated with gynecologic neoplasms as well as gastric, duodenal, and colonic malignancies.
- MNEMONIC: Peutz gets Polyps, Pigments and Pancreatic cancers
Cowden Syndrome
What is it?
What is this syndrome associated with?
- Cowden syndrome is an autosomal dominant syndrome of multiple hamartomatous polyps most commonly found in the skin and external mucous membranes, but also in the gastrointestinal tract.
- Cowden syndrome is associated with an increased risk of thyroid cancer (usually follicular), as well as skin, oral, breast, and uterine malignancies.
Cronkhite-Canada
What is this? What’s special about this syndrome compared to other similar disorders?
What are the cutaneous manifestations?
- Cronkhite-Canada is a non-inherited disorder (the only polyposis syndrome in this list that is not autosomal dominant) consisting of hamartomatous polyps throughout the gastrointestinal tract.
- Cutaneous manifestations include abnormal skin pigmentation, alopecia, and onychodystrophy (malformation of the nails).
Appendicitis
What is it?
CT’s role in appendicitis?
- Appendicitis is the most common surgical cause of acute abdomen. Acute inflammation of the appendix is thought to be due to obstruction of the appendiceal lumen, leading to venous congestion, mural ischemia, and bacterial translocation.
- Appendicitis represents a spectrum of severity ranging from tip appendicitis (inflammation isolated to the distal appendix) to gangrenous appendicitis with abscess if the disease is not diagnosed until late.
- Greater than 97% of patients undergo a preoperative CT prior to appendectomy, with resultant decrease in negative appendectomy rate from 23% in 1990 to 1.7% in 2007.
- Imaging of appendicitis relies on direct and indirect imaging findings.
What are the direct appendicitis?
What are the indirect findings of appendicitis?
- Direct findings of appendicitis are due to abnormalities of the appendix itself:
- Distended, fluid-filled appendix: 6 mm is used as cutoff for normal diameter of the appendix, although there is wide normal variability and 6 mm is from the ultrasound literature using compression. A normal appendix distended with air can measure >6 mm; therefore, some authors advocate using caution with a numeric cutoff in an otherwise normal-appearing appendix filled with air or enteric contrast.
- Appendiceal wall-thickening.
- Appendicolith, which may be a cause of luminal obstruction; however, appendicoliths are commonly seen without associated appendicitis.
- Indirect findings of appendicitis are due to the spread of inflammation to adjacent sites:
- Periappendiceal fat stranding.
- Cecal wall thickening.
- Hydroureter.
- Small bowel ileus.
Can you evaluate appendicitis via ultrasound?
If so, how?
If so, what secondary findings can be evaluated via US?
- Appendicitis can also be evaluated by ultrasound, with the key sonographic finding a tubular, blind-ending, non-compressible right lower quadrant structure measuring >6 mm in diameter. It is generally necessary to use graded compression to evaluate for compressibility.
- Secondary findings of appendicitis can be evaluated by ultrasound, including free fluid and periappendicular abscess.
Diverticulitis
Role of CT in diverticulitis?
Which side of the colon is more commonly affected?
How do you distinguish between acute diverticulitis from microperforated colon cancer? What can you recommend?
What can you do to abscesses?
Indications for surgery?
- Diverticulitis is microperforation and acute inflammation of a colonic diverticulum.
- CT is the primary modality for diagnosis, triage, and evaluation of severity and complications.
- The left colon is affected far more commonly than the right.
- It is often impossible to distinguish acute diverticulitis from microperforated colon cancer. Many authors recommend follow-up colonoscopy after the acute episode has resolved, although this recommendation is somewhat controversial and varies by institution.
- Abscesses can usually be drained percutaneously.
- Indications for surgery include the presence of a fistula or recurrent diverticulitis, with two prior episodes of diverticulitis treated conservatively.
Epiploic Appendagitis
What is it?
Who does it usually affect?
Imaging appearance?
Treatment?
- Epiploic appendagitis is a benign, clinical mimic of diverticulitis caused by torsion of a normal fatty tag (appendage) hanging from the colon.
- This condition usually affects patients in their 2nd to 5th decades with a predilection for women and obese individuals, presumably due to larger appendages
- Epiploic appendagitis has a pathognomonic imaging appearance of an oval fat-attenuation lesion abutting a normal colonic wall, with mild associated fat stranding. A central hyperdense dot in cross-section represents the thrombosed central vein of the epiploic appendage.
- Treatment is with anti-inflammatories, not antibiotics or surgery.
What is uncomplicated diverticulitis?
CT findings?
Treatment?
- Uncomplicated diverticulitis does not have any imaging evidence of bowel perforation (even though histopathologically all diverticulitis is associated with bacterial translocation across the bowel wall).
- CT findings of uncomplicated diverticulitis include
- bowel wall thickening
- pericolonic fat stranding, usually centered around a culprit diverticulum.
- Uncomplicated diverticulitis is typically treated conservatively.
What is complicated diverticulitis?
CT findings?
- Complicated diverticulitis implies the presence of an additional complication, including:
- Pericolonic or hepatic abscess (abscesses can be drained percutaneously).
- Extraluminal air.
- Bowel obstruction.
- Bowel fistula (colovesical fistula most common, apparent on imaging as gas in the bladder not explained by Foley catheter placement).
- Mesenteric venous thrombosis.
Peritoneum
What is it?
What is the visceral peritoneum? How about the parietal?
What is the most dependent portion of the peritoneal cavity?
- The peritoneum is a thin membrane consisting of a single layer of mesothelial cells that are supported by subserosal fat cells, lymphatic cells, and white blood cells.
- The visceral peritoneum lines the surface of all intraperitoneal organs, while the parietal peritoneum lines the outer walls of the peritoneal cavity.
- The most dependent portion of the peritoneal cavity (both supine and upright) is the pouch of Douglas in women and the retrovesical space in men.
Mesentery
What are the three true mesenteries? What does each contain, what do they supply/hold?
What are the other two specialized mesenteries? Where do they attach?
Where does peritoneal fluid get resorbed?
- There are three true mesenteries, which each supply a portion of the bowel and connect to the posterior abdominal wall. Each mesentery consists of a network of blood vessels and lymphatics, sandwiched between the peritoneal layers. The three true mesenteries are:
- Small bowel mesentery: Supplies both the jejunum and ileum. oriented obliquely from the ligament of Treitz in the left upper quadrant to the ileocecal junction in the right lower quadrant.
- Transverse mesocolon: mesentery to the transverse colon, connecting the posterior transverse colon to the posterior abdominal wall.
- Sigmoid mesentery: mesentery to the sigmoid colon.
- The greater and lesser omentum are specialized mesenteries that attach to the stomach. The greater and lesser omentum do not connect to the posterior abdominal wall.
- Greater omentum: Large, drape-like mesentery in the anterior abdomen, which connects the stomach to the anterior aspect of the transverse colon.
- Lesser omentum: Connects stomach to the liver.
- Peritoneal fluid is constantly produced, circulated, and finally resorbed around the diaphragm, where it eventually drains into the thoracic duct.
Gastrointestinal Carcinoid
Prevalence compared to other GI malignancies?
Where is this tumor most commonly located?
Where does it usually arise? How does it spread to the mesentery and how often does it do so?
Classic imaging appearance of carcinoid affecting the mesentery? What does the classic imaging appearance represent? What is a common finding?
- Gastrointestinal carcinoid is a relatively rare tumor compared to other gastrointestinal malignancies but is the most common small bowel tumor. It typically occurs in the distal ileum.
- Carcinoid usually arises as an intraluminal mass and may secondarily spread to the mesentery either by direct extension or lymphatic spread. Up to 80% of carcinoids spread to the mesentery.
- A classic imaging appearance of carcinoid affecting the mesentery is an enhancing soft-tissue mass with radiating linear bands extending into the mesenteric fat. Calcification is common.
- The radiating linear bands do not represent infiltrative tumor but are the result of an intense desmoplastic reaction caused by the release of serotonin by the tumor.
Sclerosing Mesenteritis
What is it?
Imaging appearance?
What is mesenteric panniculitis? CT appearance?
- Sclerosing mesenteritis is a rare inflammatory condition that leads to fatty necrosis and fibrosis of the mesenteric root.
- Imaging of sclerosing mesenteritis shows mesenteric masses with striations of soft tissue extending into the adjacent fat. Calcification may be present.
- Mesenteric panniculitis is a variant where inflammation predominates and presents as acute abdominal pain. on CT, there is a “misty” mesentery, sometimes with linear bands of soft tissue representing early fibrosis.
Mesenteric Mets and Lymphoma
What primary cancers metastasize to mesenteric lymph nodes?
What is the “sandwich” sign?
- Gastric, ovarian, breast, lung, pancreatic, biliary, colon cancer, and melanoma can metastasize to mesenteric lymph nodes.
- Mesenteric lymphoma can produce the sandwich sign, where the mesenteric fat and vessels (the sandwich filling) are engulfed on two sides by bulky lymphomatous masses (the bread).
Peritoneal Carcinomatosis
What is it?
What does “omental caking” describe?
What is the most common tumor type to cause peritoneal carcinomatosis?
One must not confuse peritoneal carcinomatosis with what other entity?
- Peritoneal carcinomatosis represents disseminated metastases to the peritoneal surface.
- The term omental caking describes the replacement of omental fat by tumor and fibrosis.
- Mucinous adenocarcinoma is the most common tumor type to cause peritoneal carcinomatosis. Peritoneal carcinomatosis due to mucinous adenocarcinoma should not be confused with pseudomyxoma peritonei!
Pseudomyxoma Peritonei
What is it?
What produces it? What other places may produce it?
What is it often associated with?
Previously, what was thought to produce it?
Tumor deposits spread where and due to what?
Clinical presentation?
CT appearance?
What is the pathognomonic sign in advanced disease?
Treatment?
- Pseudomyxoma peritonei is a low-grade malignancy characterized by copious mucus in the peritoneal cavity.
- In general it is thought to be produced by a mucin-producing adenoma or adenocarcinoma of the appendix; however, there is some controversy as to whether the ovary or colon can be a primary site as well.
- It is often associated with an ovarian mass (up to 30% of female patients), but it is thought that these are most often metastatic deposits.
- It was previously thought to be produced by a benign appendiceal mucocele, which is now believed to occur much less common than originally thought.
- 20% of all appendiceal adenomas or adenocarcinomas will cause pseudomyxoma peritonei.
- Only 2% of all appendiceal mucoceles (which occur slightly less commonly than appendiceal adenomatous lesions) will cause pseudomyxoma peritonei.
- Tumor deposits tend to be spread throughout the entire peritoneal cavity due to intraperitoneal fluid currents.
- Clinically presents with recurrent mucinous ascites. The surgeons refer to the mucinous ascites as a “jelly belly.”
- CT shows lobular ascites that is typically of slightly higher attenuation (5-20 HUs) compared to fluid ascites. Occasionally, mucus can be seen in the region of the appendix, but the flow of peritoneal contents tends to spread the mucinous ascites diffusely throughout the peritoneum.
- Advanced disease shows pathognomonic scalloping of the hepatic margin.
- Treatment continues to evolve, but the best outcomes are primarily with surgical treatment and hyperthermic intraperitoneal chemotherapy lavage.
