Radiographic Anatomy of the Abdomen: Gastrointestinal Tract

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Radiographic Anatomy of the Abdomen
Gastrointestinal Tract

• Andrew Gendler, DVM
• Radiology resident

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Abdomen Basics

• Views included
• Ventrodorsal(VD) and lateral views.
• Ability to identify structures depends on
  contrast between the 5 opacities
• Gas, fat, soft tissue/fluid, bone/mineral, metal
  
• Amount of fat is important
• Lack of contrast little abdominal fat/brown
  fat-juvenile
• animal or peritoneal effusion
• Contrast study
• Negative (air), positive (barium or iodinated
  contrast media)

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Positioning
lateral
VD
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lateral
VD
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Evaluation abdominal study

• Knowledge of normal radiographic appearance of
  abdominal organs
• Roentgen signs Size, shape, number, location,
  margination, radiopacity
• Recognition of pathologic conditions

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Follow the food though the GI
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Anatomy of the GI-Tract
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Esophagus

• Cervical, thoracic and abdominal portion
• Usually not seen radiographically
• May contain a small volume of gas (Anesthesia,
  dyspneic or nervous patients)

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Esophagus - dog
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Esophagus - cat
Herringbone pattern smooth muscle in distal 1/3
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Stomach

• Usually easily identified because it contains gas
  and/or heterogeneous ingesta
• Four regions of the stomach can be identified
  (different distribution between dog and cat)
• Cardia
• Fundus LARGEST PORTION
• Body
• Pylorus (antrum and canal)

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Stomach Canine Feline
L
R
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Stomach

• Appearance of the stomach varies with patient
  positioning
• GRAVITY dependent movement of stomach contents
• fluid and ingesta move down (dependent portion)
• gas will move up (non dependent portion)
• Helps to highlight
• various areas of the stomach

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Lets dance Radiology dance

• Use LEFT arm near your abdomen and Rockn Roll.
  Right and left, up and down!
• Fist (Pylorus)
• Forearm (Body)
• Biceps (Fundus)

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May the gravity be with you
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Ventrodorsal

• Gas located in body, near midline
• Some gas in pyloric antrum
• Fundus and pyloric canal usually contain fluid

L R L
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Ventrodorsal
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Dorsoventral

• Gas in fundus and pyloric canal
• Fluid in body

R
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Dorsoventral
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Left Lateral Recumbency

• Gas present in the pyloric antrum and canal
• Fluid in fundus

R
Cr Cd
Cr Cd
L
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Left Lateral Recumbency
PYLORUS
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Right Lateral Recumbency

• Gas is in the fundus
• Rugae may be well outlined
• Fluid moves to the pylorus
• Pylorus may appear as a discrete, round ball

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Right Lateral Recumbency
Fundus
Pylorus
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Gastric axis
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Duodenum

• Descending duodenum is fixed by
• hepatoduodenal ligament cranially
• duodenocolic ligament caudally
• Lies along right abdominal wall in VD view,
  mid-abdomen on lateral
• Landmark for the pancreas

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Duodenum
VD or DV?
VD, its VFF
VD Gas in body Fluid in fundus
VD OR DV?
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Other Small Intestine

• Should be evenly distributed through abdomen, not
  clumped, pushed over into a corner
• Exception in obese animals, particularly cats
• Loops should be relaxed and gas caps and bubbles
  should have rounded margins

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Other Small Intestine

• Contents should have homogeneous fluid opacity
• Bowel wall thickness CANNOT be assessed on survey
  radiographs
• The contents silhouette with the wall and cant
  be distinguished
• Wall measurement on ultrasound or with barium
  GI-study

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Small intestine
Cat
Dog
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Measurements

• Intestine is measured to help determine etiology
  of vomiting and provide an objective reference
  point.
• Measure from serosa to serosa.
• Compare intestinal width to Vertebral Body
  End-plate 2nd or 5th lumbar vertebra
• Duodenum 1.5 x width of VBE
• Jejunum/ileum 1 x width of VBE
• Colon 2.5 x width of VBE
• 1 segment gt 50 larger than other small
  intestinal loops (2 populations)

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Measurement
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Small intestinePositive contrast study (barium)
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Normal variations
Cat duodenum string of pearls
Dog duodenum Pseudoulcers
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Cecum

• Often visible in the dog as a c shaped gas
  filled structure
• Typically in the right cranial abdomen, but can
  be mobile
• In the cat, the cecum is small, lacks a distinct
  cecocolic junction, and seldom contains gas
• ? rarely identified

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Cecum and ColonDog Cat
L
R
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Cecum

• Dog

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Colon

• Ascending, transverse, and descending portion
• Contains varying amounts of gas and heterogeneous
  fecal material, or may be empty
• Typically in the shape of a question mark on VD
  view, but exact position is variable

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Colon
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Colon
Dog
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Rectum

• Portion of colon located in pelvic canal, ending
  in anus
• Primary disease of rectum and distal colon are
  rarely evaluated radiographically

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Digested-Food Exit
Questions?
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Megaesophagus
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Megaesophagus - cat
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Gastric dilatation and volvulus
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Gastric FB and pneumogastrogram (negative
contrast)
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Left lateral
Right lateral
DV
VD
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Paralytic Ileus
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Mechanical obstruction / ileus
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Linear foreign body - bunching
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Who am I?
CECUM
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Megacolon / Constipation
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Questions?