02-24 GI Tract Imaging Flashcards
OBJECTIVES: At the end of this lecture, the learner should be able to: • Describe how and why inflammation causes changes in the density of fat and solid organs on CT scans • Discuss the pros and cons of using CT vs. MRI in the diagnosis of common inflammatory processes of the abdomen such as cost, risk, availability • Discuss the technical and tumor factors that influence the ability to identify masses in the solid organs with enhanced CT • Predict the pattern of dilatation and decompressio
OBJECTIVE: How and why does inflammation cause changes in the density of fat and solid organs on CT scans?
Accumulation of fluid and inflammatory cells impacts the attenuation of inflamed structures on CT:
—Solid organs-density will usually decrease (organs are denser than fluid)
—Fat-density will increase (fluid denser than fat)
—Bowel wall- no appreciable change in density
OBJECTIVE: Discuss the pros and cons of using CT vs. MRI in the diagnosis of common inflammatory processes of the abdomen such as cost, risk, availability
—CT is faster and cheaper but more radiation, etc.
—MRI is much more $$ and time-consuming. Really only commonly used for Crohn’s, in kids or in cases where CT failed to show anything…likely we will see more use of MRI in the future.
OBJECTIVE: Discuss the technical and tumor factors that influence the ability to identify masses in the solid organs with enhanced CT
Solid organ masses are visible on CT when the difference in attenuation between the mass and normal organ parenchyma is large enough to be visible to the eye.
—IV contrast accentuates this difference, need to tell radiologist what tumor you suspect b/c it affects timing
—tumor will look different than organ: either hypo- (e.g. Colonic adenoCA met) or hypervascular (1° HCC) which illuminates BEFORE the parenchyma
OBJETIVE: Predict the pattern of dilatation and decompression which occur with obstruction of the proximal small bowel.
Not 100% sure…
—no PO contrast gets through
—air fluid level in stomach even after NPO for a while
OBJECTIVE: Predict the pattern of dilatation and decompression which occur with obstruction of the distal small bowel.
See extenseive dilation of small bowel which will have plicae circularis which are closer together than haustra and go all the way around the lumen (vs. haustra don’t)
—No PO contrast in colon
OBJECTIVE: Predict the pattern of dilatation and decompression which occur with obstruction of the colon.
See extenseive dilation of small bowel
—will have plicae circularis (closer together than haustra and go all the way around the lumen vs. haustra)
See extensive colon dilation
—will have haustra
OBJECTIVE: Why isn’t radiography sensitive for pancreatitis, appendicitis or diverticulitis?
Doesn’t pick up signs of inflammation or edema well.
Fat stranding is…?
Increased density of mesenteric fat, often as fine or smudgy strands causing hazy increased density
Indication for KUB? What do you look at when interpreting one? (OBJECTIVE: Describe the types of bowel pathology which can be seen with radiography)
Indication: pain
Take 2 views: supine and upright (or on side if can’t stand)
—Supine: look for bowel diam, fold pattern, wall thickness, gas pattern, abnl air collection (in bowel wall, portal venous system)
—Upright: look for free intraperitoneal air + air fluid levels in bowel
Indications for abdominal fluoroscopy? What does each of the two contrast methods show?
Indicated for: pain, dysphagia, diarrhea, CRC (failed colo)
Two Methods:
1. Double contrast - air + barium: good for assessing mucosa (ulcers, mucositis, neoplasms)
2. Single contrast - barium only: assess fold pattern/thickness, caliber of the lumen
Indications for abdominal CT? What types of contrast can be used? Why use each one? (OBJECTIVE: Describe the types of bowel pathology which can be seen with CT)
Indicated for: pain, bowel pathology, tumors, wt loss, vague sxs
Two types of oral contrast:
1. Positive (barium- or iodine-based) - differentiates fluid collections from bowel
2. Negative (water, low-density barium called “Volumen”, others) - better for mucosa and wall
**Remember, the radiologist prescribes the scan delay (time between administration of IV or PO contrast and initiation of image
Indications for abdominal MRI?
Indicated for: equivocal CT findings, pediatrics (no rad), iodine allergy, Crohn’s, MRCP, tumors/masses
—Not widely used b/c $$ and time-consuming, Crohn’s is really only common use
—There are PO and IV contrast options
Folds in the small bowel are called? Colon? Rectum?
—Small Bowel = semilunar folds
—COLON = HAUSTRA: small pouches caused by sacculation, which give the colon its segmented appearance. The taenia coli runs the length of the large intestine & is shorter than the intestine, so colon becomes sacculated, forming the haustra.
—Rectum = plicae circulares
SBFT is abbrev for?
Small Bowel Follow-Through (a type of fluoroscopy study)
Thumb-printing is seen with?
“Thumbprinting” may be seen in the colon. It looks as though someone has pressed their thumb from outside the wall into the bowel lumen, resulting in a lobular or nodular pattern. This is seen most commonly in the colon with:
o infectious colitis, such as pseudomembranous colitis
o inflammatory colitis, such as inflammatory bowel disease
o Bowel ischemia
