GI Imaging Pt.2 Flashcards
what is the ideal patient preparation for small intestinal imaging?
12-24 hours of fasting +/- enema
not always realistic esp in emergency cases!
describe normal small intestine variations
- gas:
-30-60% of the SI filled by gas in fasted dogs
-only a small amount of SI gas in cats - soft tissue mixed with small gas bubbles = normal ingesta
- mineral/metal:
-cat litter
-osseous fragments
-medication - REMEMBER: wall thickness cannot be determined with plain radiographs!
describe dilating diseases of the ileus
failure of the intestinal contents to move aborally
2 types
- mechanical: physical obstruction of the lumen
-origin: intraluminal, mural, extramural
-surgical treatment indicated - functional: lack of/decreased peristalsis
-no forward movement of the contents
-nonsurgical treatment
radiographic signs:
-increased intestinal diameter
-diffuse: functional ileus
-segmental: mechanical ileus
describe functional/generalized/paralytic ileus
- decreased peristalsis, no physical obstruction
- causes:
-post open abdomen
-peritonitis
-enteritis
-drugs: xylazine, opioids
-neuromuscular disease
-hypokalemia - DIFFUSE small intestinal dilation
- ddx: distal aborad mechanical obstruction and mesenteric torsion
-clinical signs are key!
-mesenteric torsion: moderate to severe diffuse intestinal dilation, poor prognosis, VERY painful! (functional ileus is not very painful)
5, radiographic features
-generalized, mild to moderate, intestinal distension (fluid or gas)
-uniform size of the intestinal loops
-normal intestinal distribution within the abdomen
describe mechanical/obstructive ileus
- acute or chronic, partial or complete
- NOTE: gravel sign
-sign of partial and chronic mechanical obstruction
-accumulation of more radiopaque (usually mineral) content just orad to the site of mechanical obstruction - origin/causes:
-intraluminal: obstructive foreign body
-mural: intussusception, stenosis, adhesion, neoplasia
-extramural: incarceration (hernias), other organ/mass compression - radiographic features:
-localized/segmental SI dilation, orad segment
–two populations of SI loops regarding size (normal and abnormal intestinal segments)
-intestinal staking and hairpin turns
-unusual/interrupted intraluminal gas pattern (comma shaped)
-unchanging or progressive appearance overtime
describe the interpretation paradigm
- serosal margins detail
-if decreased, cannot see fluid filled segments, just gas filled segments = harder to interpret - trace the colon:
-to determine which ones are the small intestinal segments
-pneumocolon - size and distribution of the small intestines
-one big confounder is the colon! need to remove from your interpretation
-usually not a big deal bc colon has a predictable location, can follow from the rectum up and running along midline of abdomen just caudal to the stomach; formed feces also helps! will only see in the colon
-can put contrast in the colon too to help - segmental or diffuse SI dilation
-mechanical vs. functional ileus
-two populations: mechanical ileus
-exception: mechanical obstruction at the level of the ICJ
*great diagnostic value of the US and CT!
describe normal SI diameters
after you remove colon from interpretation, measure the largest segment of SI
dogs:
-normal SI is = or <1.4-1.6x height of mid body of L5
-but this is very all or nothing and measurements are never perfect so prefer
-SI diameter/mid body of L5 ratio: 1.4 > X > 2.4
-between 1.4-2.4 = grey zone, could be obstructed OR not, need more info! (gas pattern, FB, areas of stricture, etc.)
cats:
-12mm, serosa to serosa
-little amounts of intraluminal gas
describe linear foreign bodies
special type of mechanical obstruction!!
- due to progressive peristalsis along a linear object
- fixed/anchored orad extremity at the base of the tongue and pyloric sphincter
- may not cause complete mechanical obstruction
- could cause perforation and peritonitis
- radiographic features:
-plicated/bunched intestinal segments
-small and tear drop and/or comma shaped intraluminal gas bubbles
like the cat that swallowed the blinds cord at VCSG and accordioned his intestines
describe intussusception
- telescoping/invagination of an intestinal segment into another contiguous segment
-intussuscipiens: outer/receiving segment
-intussusceptum: inner/entering segment - permanent versus transitional
-can cause partial or complete mechanical obstruction
-transitional very common in puppies! permanent more common in adults - target-like appearance on US
- young dogs:
-most common/frequent
-may be transitional
-secondary to enteritis and parasitism - older dogs:
-frequently associated with intestinal neoplasia - radiographic findings:
-distention of an intestinal segment with gas and soft tissue
-usually a sharp with a convex soft tissue portion surrounded by gas
-coil spring appearance
-gas orad to intussusception and just to the sides of it
describe small intestinal masses
- neoplasia:
-focal: adenocarcinoma, leiomyoma, GIST (gastrointestinal stromal tumor, focal)
-diffuse: lymphoma and mast cell tumor - oomycetes/fungal infection (focal): pythium, lagenidium
- granuloma and abscess (focal, may contain gas): gossypiboma (leaving surgical material inside the body)
- radiographic findings:
-challenging diagnosis using plain rads
-soft tissue mass
-loss of peritoneal serosal margin detail: rupture versus local inflammation
- +/- obstructive pattern: mechanical ileus
describe intestinal perforation
- due to:
-external trauma
-GI FB rupture
-ruptured neoplasia - consequences:
-peritonitis
-pneumoperitoneum: SURGICAL EMERGENCY! use horizontal beam projection to diagnose
describe anatomy of the large intestine
- question mark or shepherd’s crook shape
- cecum: right mid-abdomen
- ascending colon: right mid-abdomen, cranial to cecum
- transverse colon: caudal to the stomach and pancreas (left limb)
- descending colon:
-larger portion
-mainly left-sided and midline (aborad portion) - rectum: end, intrapelvic
- displacement of colon is helpful to determine mass effect cause!
-ventral displacement = lumbosacral LN enlargement
-dorsal displacement: bladder, prostate, uterus, etc.
describe megacolon
- more common in cats
- causes:
-more common: idiopathic and neuromuscular
-less common: stricture, pelvic canal narrowing secondary to prior trauma, neoplasia - radiographic features:
-dilation of the colon
-accumulation of more mineral opaque feces (dehydrated feces)
-ratio: <1.5x length L5
describe colonic torsion/volvulus
- large breed dogs, maybe dynamic, poor prognosis
- radiographic features:
-gaseous segmental dilation of the colon
-abnormal displacement of the descending colon to the right of midline
-displaced cecum: to the left of midline
