Diagnostic Imaging of the Abdomen

Question 1

Approach to the assessing abdominal radiographs.

Answer 1

Systematic.
Check periphery of the film.
Carry out an overall assessment:
- skeletal structures.
- body wall intact?
- serosal detail.
Look at every organ system.

Question 2

Abdominal organs/structures and their visibility on plain radiographs.

Answer 2

See - liver, spleen, stomach, SI, LI, kidneys, bladder, fat.
Don’t usually see - pancreas, adrenals (unless calcified), LNs, ureters, urethra, ovaries.
May see - prostate, uterus, aorta/CVC.
depends on size of structure, abdominal fat, physiology e.g. enlarged uterus close to oestrus.

Question 3

Difference between normal cat and normal dog abdominal radiographs.

Answer 3

Cats have prominent areas of falciform and retroperitoneal fat - no as common in the dog.
Dog spleen lies in a different position to cat - tail of the spleen usually curls around in the mid-ventral abdomen (more commonly visible in dogs than in cats).

Question 4

What types of body wall rupture may be seen on abdominal radiograph?

Answer 4

Ventral wall rupture.
Perineal rupture.
Diaphragmatic rupture.

Question 5

When is serosal detail of organs/structures on abdominal radiograph good?
When is it poor?

Answer 5

Good if there is fat present.
Poor if:
- young/thin animal.
- animal has a peritonitis.
- there is flid in the abdomen.
- neoplasia in the abdomen.

Question 6

How to make an assessment of serosal detail.

Answer 6

Check body condition:
- intra-abdominal fat.
- fat over spinous processes.
Distension of abdomen?
- unlikely if very thin animal.
- free fluid?
Free gas?
- possible GI rupture.
- previous surgery / trauma.

Question 7

Spleen on abdominal radiograph.

Answer 7

Usually visible in dogs on both projections.
- lateral – mid-ventral abdomen.
- VD/DV – caudal to stomach and cranial to L kidney.
Less commonly seen in cats on lateral view.
Head of spleen caudal to stomach on the left (seen on VD).
Tail usually mid ventral abdomen (lateral view).
Size variable depending on:
- sedation (may cause enlargement).
- position.
- individual / breed variation (GSD larger spleen).

Question 8

Diffuse splenomegaly on abdominal radiograph.

Answer 8

Hard to assess radiographically.
- wide normal range,
- overlap between maximum normal / minimum pathological size.
- subjective.
Look at margins and try to assess if rounded.
May help to look if there is any displacement of other viscera adjacent to the spleen.

Question 9

Further investigations of suspected splenomegaly.

Answer 9

Ultrasound to assess how homogeneous parenchyma is.
Aspirates for cytological assessment.

Question 10

Splenic masses.

Answer 10

Commonest cause of ventral midabdominal mass.
Small intestinal displacement - caudally or dorsally.
Masses may bleed - free fluid / poor detail.

Question 11

Normal liver on abdominal radiograph.

Answer 11

Roughly triangular in shape.
Soft tissue opacity.
Smooth, distinct margins.
Ventral lobe - not too rounded, approx. at level of costal arch (breed dependent).
‘Gastric axis’ helpful to assess liver size.
- normal = perpendicular to spine + parallel to ribs.
- breed variation in dogs.
May see gall bladder ventrally in cat.

Question 12

Differentials for a small liver?

Answer 12

Portosystemic shunt.
- dogs may also have enlarged kidneys.
Cirrhosis.
Chronic hepatitis.

Question 13

Differentials for a large liver.

Answer 13

Acute hepatitis.
Endocrine hepatopathy e.g. Cushing’s disease / long-term steroid treatment.
Congestion (venous).
Infiltrative neoplasia.
Focal mass lesion.
- neoplasia.
- cyst.
- abscess.
- granuloma.

Question 14

Normal stomach on abdominal radiograph?

Answer 14

Lies in cranial abdomen.
Caudal to the liver.
Long axis = parallel to the ribs.
May contain food.
Fluid/gas distribution varies w/ position.
- L lateral – fluid dorsally in the fundus.
- R lateral – fluid ventrally in the pylorus (and extends into duodenum.
- DV - fluid in the gastric body.
- VD - fluid in the fundus and pylorus.

Question 15

Information to be gained about the stomach on plain radiograph?

Answer 15

Position:
- hiatal hernia.
- gastro-oesophageal intussusception.
- diaphragmatic rupture.
- dilation (no subdivision) vs volvulus (compartmentalised).
Contents:
- radiopaque foreign material.
Transit time of food/liquid:
- to assess for outflow obstruction.
*however, plain radiographs usually unrewarding.
- wall cannot be delineated from fluid content unless there is rugal calcification (unusual).

Question 16

Normal small intestine on abdominal radiograph.

Answer 16

Lies in the mid abdomen.
Usually contains fluid/gas - wall thickness uncertain w/o contrast.
Variable diameter loops:
- usually around twice the width of a rib.
- usually around equal to the depth of a vertebral end plate.

Question 17

Dilated SI on abdominal radiograph.

Answer 17

Ratio of width SI to height of mid-body of L5.
- SI:L5 <1.4 – V unlikely to be obstructed.
- SI:L5 >2.4 – V likely to be obstructed.
Ratio of width of largest and smallest loops.
- <2 – v unlikely to be obstructed.
- >3.4 v likely to be obstructed.
Dogs w/ values falling between the 2 require further assessment (ultrasound, upper GI series).

Question 18

Chronic partial obstruction on abdominal radiograph.
Differentials for this.

Answer 18

‘Gravel sign’.
Chronic build up of ingesta overtime.
Looks like faeces but not in the colon.
Differentials:
- intussusception.
- FB.
- tumour.
- stricture.

Question 19

Normal colon on abdominal radiograph.

Answer 19

Ascending in right mid abdomen.
Transverse crosses caudal to stomach.
Descending in left abdomen.
Rectum w/in pelvic canal.
Normally contains faeces / gas.

Question 20

Colon size on abdominal radiograph.

Answer 20

Dogs colonic width should not exceed:
- 3x that of normal SI.
- length of body of L7.
– >1.5x likely to indicate dysfunction.
Cats:
- <1.3x length of L5 suggests normal.
- >1.5x length of L5 is good indicator of megacolon.

Question 21

Why are plain radiographs helpful for assessment of the colon?

Answer 21

Size (megacolon).
Shape.
Contents.
Position e.g. displacements etc.

Contrast studies rarely performed now.
- colonoscopy preferred.

Question 22

1. What are contrast media?
2. What do contrast media do?
3. Purpose of using contrast media?

Answer 22

1. Agents that are more or less opaque than surrounding tissue.
2. They delineate organs / cavities w/in the body.
3. To see structures not normally visible or poorly visible - e.g. ureters, urethra, spinal cord.
   To gain more info about soft tissue structures.
   - bladder, kidneys, GI tract.

Question 23

Types of contrast media.

Answer 23

Positive contrast - high atomic number.
– barium, iodine.
–> white on radiograph.
Negative contrast - low density.
- gases (air, CO2).
– black on radiograph.

Question 24

Contrast media - barium.

Answer 24

Used in GIT.
Various forms - powder, suspension.
Inert, non-toxic.
Reasonably palatable.
Cheap.
Good mucosal detail (liquid barium).
No osmotic effect (not significantly diluted as moves through GIT).

Question 25

Contrast media - iodine.

Answer 25

Water-soluble organic iodine-containing preparations.
2 main groups:
- ionic.
– disadvantageous –> irritant extra-vascularly, toxic in large doses (do not repeat studies multiple times), viscous (reduce by warming before use), contraindicated IV in cardiovascular or renal insufficiency, contraindicated for myelography which involves introduction into sub arachnoid space (can induce seizures and arachnoiditis).
- non-ionic.
– can be used for all studies.
– disadvantages –> slightly more expensive, viscous, side effects (incl. anaphylaxis, nephrotoxicity, urticaria, vomiting, pyrexia) may still occur, although rare.
IV use.
Renal excretion.

Question 26

Negative contrast media advantages.

Answer 26

Cheap (or free).
Simple to use.
Relatively safe.
Can combine w/ positive contrast agents for a double contrast study.

Question 27

Negative contrast media disadvantages.

Answer 27

V small risk of air embolism.
- reduce risk by performing study in left, rather than right, lateral recumbency.
Poor mucosal detail.
Produce less contrast than positive contrast agents.

Question 28

Principles for performing contrast radiography.

Answer 28

Indications - will the lesion be demonstrable:
– time and cost.
Correct preparation - e.g. enema.
Restraint.

Question 29

What should always be done before a contrast study?

Answer 29

Take plain radiographs.
Check radiographic quality - exposure factors, positioning, centring.
Check patient preparation - e.g. empty colon.
Look for a radiological diagnosis - is a contrast study necessary?
Look for radiopaque lesions that may be obscured by contrast.

Question 30

Means of determining how much contrast should be administered.

Answer 30

Palpation of the organ you are administering the contrast agent into e.g. bladder.

Question 31

What is…
1. Portovenography?
2. Arthrography?
3. Angiography?
4. Fistulography?

Answer 31

Contrast imaging of…
1. Portal vein and tributaries.
2. Joints.
3. Blood vessels.
4. Sinus tracts.

Question 32

1. indications for a barium swallow?
2. What does a barium swallow show?
3. In what forms can the barium be administered?
4. What risk if swallowing problem, struggling, resp. distress, weak?

Answer 32

1. dysphagia, regurgitation, suspected oesophageal rupture.
2. Pharynx and oesophagus.
3. As liquid barium and/or barium mixed with food.
   - use water-soluble iodinated contrast if suspect rupture.
4. Risk of aspiration - care.

Question 33

1. What does a barium ‘follow-through’ study evaluate?
2. What agent type should be used for this?
3. How can the agent be administered?
4. Taking the radiographs?
5. When would the final images be taken?

Answer 33

1. Stomach and SI.
2. Liquid barium.
3. By mouth or stomach tube.
4. Immediately and then at intervals depending on transit time.
5. At 24hrs post barium or when all barium is in the colon.

Question 34

Indications for barium GIT study.

Answer 34

Vomiting.
- persistent, recurrent.
- haematemesis.
Palpable mass.
Abnormality suggested by survey films.

Question 35

Complications of barium study?

Answer 35

Constipation (rare).
Aspiration (if given by mouth).

Question 36

Normal variants of upper GI series.

Answer 36

‘String of pearls’ appearance - due to sequential peristaltic contractions.

Duodenal ‘pseudo-ulcers’ - due to mucosal indentations – associated with lymphoid tissue –> normal as long as only in the duodenum and only on one side.

Question 37

1. What does a barium enema evaluate?
2. Disadvantages of barium enema.
3. Indications for barium enema?
4. What alternative may be better than barium enema?

Answer 37

1. Large intestine.
2. Messy and difficult to interpret (need to perform normal enema beforehand .
   3.Dyschezia, haematochezia, palpable mass.
3. Ultrasound, endoscopy