Contributors: Fraser McConnell
Species: Canine | Classification: Miscellaneous
- Radiological examination forms a vital role in the investigation of gastrointestinal tract disease.
- Radiography allows evaluation of shape and position of gastrointestinal tract.
Significant gastrointestinal disease may be present despite normal radiological appearance.
- Contrast radiography is required for full evaluation of the gastrointestinal tract.
- Positional radiography is often useful particularly in gastric disease.
- Taking both lateral projections Radiography: thorax may reduce risk of missing gastric masses.
- A low KVp and high mAs should be used to maximize contrast of abdominal radiographs.
- A grid is necessary if the depth of tissue is >10 cm.
- Care should be taken to include the entire gastrointestinal tract for most investigations.
Sedation and general anesthesia will affect gastrointestinal motility.
- Contrast studies may be performed under sedation with acepromazine and buprenorphine which have least effect on function.
- The stomach lies parallel with the ribs or perpendicular to the lumber vertebrae.
- Position may be affected by liver size.
- The fundus lies dorsally and to the left of the midline.
- The pylorus is ventral on the right hand side.
- Positioning the dog in right lateral recumbency allows the pylorus to fill with fluid and it may appear spherical.
This appearance may mimic a gastric foreign body .
- In immature dogs the pylorus may be situated closer to the midline than in adults.
- The position of the small intestine is largely dependent on the size and position of other abdominal organs.
- Primary alteration in position of the small intestine is rare.
- The small intestine however should form natural soft loops.
- Diameter of small intestine is usually relatively uniform and can be assessed by comparison with the diameter of the ribs or lumbar vertebrae.
- In deep-chested dogs the small intestine may appear bunched on the right side of the abdomen.
Large intestine and colon
- The cecum is often gas filled and appears as an ovoid lucency in the mid-abdomen on the right side adjacent to the ascending colon link .
- The colon forms a question mark shape on the VD projection.
- It can be recognized by its larger diameter than the small intestine and the presence of feces within its lumen.
- Occasionally contrast studies, eg pneumocolon Radiography: large intestine contrast are required to differentiate colon from small intestine.
- The transverse colon lies adjacent to the greater curvature of the stomach and to the left of the pancreas.
- The normal diameter of the colon is less than the length of L2.
- Depends on content.
- Cranial wall contacts liver, part of cardia touches diaphragm .
- A line drawn from cardia to pylorus should be parallel to 12th intercostal space in normal animals.
- On VD projection pylorus is in midline.
- Very variable depending on contents which may be fluid or gas.
- Can be divided into 4 parts:
- Cardia - where esophagus enters.
- Fundus - to the left and dorsal to the cardia.
- Body - main part of the stomach.
- Pylorus - where the duodenum exits the stomach.
- Width should be less than that of lumbar vertebral body in normal animal.
- Location varies except for proximal duodenum which exits pylorus courses cranially before turning right and caudally.
- Variable as can contain gas or air.
- Gentle curving loops.
Large intestine and colon
- Colon should be 2-3 times width of normal small intestine.
- Colon starts at cecum (ventral to L2/L3) and in cats is less spiral than in the dog.
- Ascending colon becomes transverse colon caudal to stomach and then bends caudally to become descending colon.
- May contain gas or fecal material which often has mottled density.
- Misinterpretation of spherical pylorus full of fluid as gastric foreign body.
Other imaging modalities
- Allows assessment of structure and thickness of gastrointestinal tract wall which is not possible with plain contrast radiography.
- Introduction of contrast (gas or barium) into stomach, intestine or colon allows better assessment of position.