Contributors: Fraser McConnell

 Species: Canine   |   Classification: Miscellaneous

Introduction

Overview

  • 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.

Radiographic considerations

  • 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.

Restraint

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.

Indications

Radiographic anatomy

Stomach

  • 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 Stomach normal pylorus mimicking mass - radiograph lateral.
  • In immature dogs the pylorus may be situated closer to the midline than in adults.

Small intestine

  • 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 Abdomen: normal female (caudal) radiograph lateral.
  • 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.

Interpretation

Stomach

Size

  • Depends on content.

Position

  • Cranial wall contacts liver, part of cardia touches diaphragm Abdomen: normal 01 radiograph lateral.
  • A line drawn from cardia to pylorus should be parallel to 12th intercostal space in normal animals.
  • On VD projection pylorus is in midline.

Opacity

  • Very variable depending on contents which may be fluid or gas.

Appearance

  • 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.

Small intestine

Size

  • Width should be less than that of lumbar vertebral body in normal animal.

Position

  • Location varies except for proximal duodenum which exits pylorus courses cranially before turning right and caudally.

Opacity

  • Variable as can contain gas or air.

Appearance

  • Gentle curving loops.

Large intestine and colon

Size

  • Colon should be 2-3 times width of normal small intestine.

Position

  • 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.

Opacity

  • May contain gas or fecal material which often has mottled density.

Pitfalls

  • Misinterpretation of spherical pylorus full of fluid as gastric foreign body.

Other imaging modalities

Ultrasonography

  • Allows assessment of structure and thickness of gastrointestinal tract wall which is not possible with plain contrast radiography.

Contrast studies

  • Introduction of contrast (gas or barium) into stomach, intestine or colon allows better assessment of position.