This session will cover radiographic and ultrasound imaging of the gastrointestinal tract. Many basic principles and "older"
techniques will be discussed. Newer techniques including MR and CT imaging will be briefly discussed.
Having evaluated the radiographs carefully and systematically, it is vital important to consider the radiographic findings
in light of the clinical signs. There may be clinical findings, which are of no clinical importance or of no significance
at the current time. There may be abnormalities which were not expected in light of the present signs but which warrant further
investigation. Finally there may be an abnormal finding, which can be linked wholly, or in part to the findings presenting
problems and either allow a definitive diagnosis to be made or inform further investigations.
There are clinical situations where it is important to make a rapid, yet informed, decision that surgery is required immediately
or as soon as the patient can be stabilized, rather than further diagnostic tests. Equally it is not in the best interests
of the patient for exploratory laparotomy to be considered a routine means of investigating unexplained signs. Radiographic
features of the gastrointestinal tract which indicate the need for urgent surgery include:
- Distension and volvulus of the stomach
- Abnormal small intestinal distension in the presence of normal electrolytes levels
- Free air in the peritoneum, which cannot be explained by recent laparotomy, abdominocentesis or a defect in the abdominal
- Mottled or streaky gas lucencies in the bowel loops indicative of necrosis
- Overall loss of abdominal detail associated with a septic abdomen, this should be confirmed by cytological testing of the
Contrast Radiography (discussed in a following session)
Contrast techniques should be considered when the plain radiographic findings are insufficient to be confident about a diagnosis,
but are of concern to further investigate the case. Contrast procedures allow further evaluation of the gastrointestinal tract.
When planning a contrast it is very important to:
- Be thoroughly familiar with the procedure
- Have properly prepared the patient for the procedure.
- Have the appropriate contrast medium
- Understand the possible complications and be prepared for these complications
Contrast radiography will be discussed in a following session.
Diagnostic ultrasound is widely available and offers great potential in the evaluation of the gastrointestinal tract. Not
only can ultrasound allow internal architecture of structures to be seen, but also very small structures, such as lymph nodes,
can be identified and assessed. Ultrasound should not supplant radiography for the overall evaluation of the abdomen and should
be used specifically to answer particular clinical questions or as a supplement to radiographic investigations. Radiography
and ultrasound are complimentary procedures and it is often very useful to use both modalities. Abdominal ultrasound is far
superior in the investigation of fluid accumulation, but not very useful with large volume free gas in the abdomen.
All portions of the gastrointestinal tract are composed of 5 acoustic layers
The most important factor affecting the variation of the radiographic appearance of the stomach is the patient positioning.
Indeed the view directly influences the way in which gas and fluid contents are positioned relative to each other in the gastric
lumen. Fluid falls to the dependent portion of the stomach whereas gas rises. In the VD view the gas is in the body, crossing
the midline of the dogs body. In the DV projection the gas is more likely to be purely in the gastric fundus in the left abdomen.
In left lateral recumbency the gas will be right sided in the pylorus and duodenum. This positioning dependency can used to
clinical advantage to highly certain lesions or surround lesion with gas for better evaluation. Lesions in the gastric outflow
tract or duodenum are seen better in left lateral projections. The stomach wall thickness can only be evaluated with contrast
radiography and the attempt to determine wall thickness on plain images is fraught with error.