SA GI radiography and Ultrasonography Flashcards
What are the advantages and disadvantages of GI radiography?
Advantages:
- Gives a global overview
- Assessment of adjacent thorax and skeleton
- Good for detecting gas or mineralisation
- Very useful for acute conditions (particularly vomiting)
- Cheap and widely available
Disadvantages:
- Superimposition of structures
- Lack of inherent radiographic contrast (cf. thorax)
- Soft tissue and fluid appear the same (water radiopacity)
- Magnification
- Less useful for chronic conditions (particularly diarrhoea)
Describe radiographic technique challenges?
Challenges include:
- Low inherent contrast (soft tissue/fluid and fat)
- Low kV
- Minimising scattered radiation
- Low kV, collimation, use of a grid
- Avoiding movement blur
- Appropriate chemical and physical restraint
- Adequate patient preparation
- Fasted, empty bladder and bowels, clean coat
- 24 hours starvation if possible (free access to water)
Describe good radiographic technique for GI?
- Two orthogonal views: one lateral and a VD
- So the organs spread out
- Centre on the caudal border of the last rib
- Take the radiograph during the expiratory pause
- The diaphragm is most cranial so the organ spread out making them easier to see
Describe GI and Liver contrast studies?
- Document function by taking of sequential still images (e.gbarium series) or using real-time radiography (fluoroscopy)
Gastro-intestinal tract*
- Barium swallow (fluoroscopy)
- Gastrography(air, barium or double contrast)
- Barium series (or “follow-through”)
- Barium enema
- Pneumocolon
Liver
- Mesenteric portovenography(water- soluble iodine)
* Water-soluble iodine may be used with suspected perforations
What GI strucures are visible and not visible in radiography?
The following structures are normally visible in survey radiographs:
Liver, stomach, spleen, kidneys (right variable in dogs, esp. cranial pole), small intestine, caecum, colon, urinary bladder, prostate gland, diaphragm, body wall, sublumbar musculature, thoracolumbar/lumbar vertebrae, caudal ribs, part of bony pelvis.
The following structures are not normally seen in survey views:
Adrenal glands (occasionally calcified in cats), gall bladder, ovaries, uterus, mesentery, mesenteric lymph nodes, omentum, pancreas, abdominal aorta, abdominal vena cava.
The most important GI landmarks are?
The most important landmarks are:
- Liver
- Stomach
- Spleen
- Kidneys
- Small intestines
- Colon
- Urinary bladder
Should be able to see these structures on a radiograph if we can’t see we ought to think why they are being displaced or hidden
What are the advantages and disadvantages of GI ultrasound?
Advantages:
- Assessment of internal architecture and vasculature
- Real time assessment/motility
- Good soft tissue definition
- Accurate measurement
- FNA/biopsy guidance
Disadvantages
- Limited field of view
- Difficult with large amounts of gas
- Very equipment and operator dependent
Ultrasound and radiography are complementary as the advantages and disadvantages of each are different
Increasing the frequency of an ultrasound probe results in?
Less tissue penetration and more definition. So use highest frequency that allows you to see tissue of interest.
What are radiographic and ultrasound signs to observe?
Radiographic signs
- Number
- Location
- Size
- Shape
- Margination
- Radiopacity
- (Internal architecture)
- (Function)
Ultrasonographic signs
- Number
- Location
- Size
- Shape
- Margination
- Echogenicity
- Internal architecture
- Function
Radiographic changes are often due to?
- changes in the size and shape of adjacent structures
- the presence of an abnormal structure
- the absence of a normal structure
How can ultrasound images be assessed?
Internal architecture
which structure(s) are affected
- e.g. spleen, liver, mesentery
where is the lesion within the tissue / organ
- Peripheral or central, diffuse or localised
- Position in relation to anatomical landmarks e.g. blood vessels
When assessing size of structures on radiography what must be considered?
Remember that several organs can undergo considerable physiological distension
e.g. stomach, bladder, uterus
When comparing to normal sizes what must you be careful of?
Compare to known normals where possible, but beware overinterpretation!
Compare the shape of a normal spleen and an abnormal one on radiography?
Discuss margination with regards to radiography?
- In the normal abdomen, mesenteric fat highlights the serosal surface of the abdominal organs
- Structures of the same opacity in contact with each other will appear to merge into one radiographic shadow = border obliteration (border effacement/silhouette sign)
- e.g. loss of abdominal detail in the presence of abdominal fluid
Discuss margination in ultrasonagraphy?
Describe the lesion in terms of margins and outline
- e.g. –abscesses have a fibrous capsule, clear margins, well defined outline and shape, and are distinct from normal tissue
- malignant tumours may have ill defined margins and irregular contours and are poorly defined from adjacent tissue Margination
How do different tissue appear on radiography?
The thickness of an area determines the opacity. Large amount of gas is more lucent than a small amount.
How should echogenecity be assessed?
- What is the normal echogenicity of the affected tissue?
- Is the echogenicity increased or decreased within any lesion?
- Is the echogenicity normal, increased or decreased in the surrounding tissues?
What is the comparitive echogenecity of liver, spleen and renal cortex in the dog?
Spleen > Liver = Renal Cortex
How should renal architecture be described in ultrasonography?
- Changes in normal architecture
- relate to the normal architecture of that organ
- Is the tissue homogenous or heterogenousin echogenicity?
- Is there increased vasculature?
- relate to the normal architecture of that organ
Discuss the position of the liver in a lateral radiograph?
Roughly triangular in shape with smooth distinct margins
Soft tissue opacity
Demarcated by the diaphragm cranially and the stomach caudally
- Gastric axis should be parallel to the ribs and perpendicular to the spine (lateral)
- perpendicular to the spine (VD)
Ventral lobe
- Fairly sharp angle
- Contained within costal arch (caudal edge)
- May see gall bladder ventrally in cat
What can be seen here?
Hepatomegaly
- Projection of caudoventral margin of liver well beyond the costal arch
- Rounding of caudoventral angle
- Caudal displacement of stomach axis
What is wrong here?
Small liver
- Cranial displacement of stomach
- Absence of caudoventral angle
- Significance dependent on clinical signs, etc.
If liver looks small may be due to breed as deep chested e.g sighthounds
Discuss ultrasound of the liver?
- Majority of liver is examined from ventral abdomen immediately caudal to xiphisternum
- The probe should be fanned from left to right in sagittal section, then from cranial to caudal in transverse section
- Reference point is the diaphragm
- Thin, hyperechoic line which moves with respiration
What can be seen at different probe points?
Look at the ultrasound of the liver in the transverse image?
What is this?
Normal gall bladder with acoustic enhancement artefact
What is this?
Bile sediment
What is this?
Wall thickening (e.g cholecystitis)
What is this?
Choleliths
Compare generalised and focal abnormal liver parenchyma?
Discuss ultrasound of abnormal hepatic parenchyma?
- Ultrasound is sensitive for detecting architectural changes, but is very non-specific
- Therefore, histopathology remains essential for diagnosis of liver disease
Discuss the view of the spleen on radiograph?
The spleen
- Location and size variable
- Smaller in the cat (usually not visible on lateral views)
- Flattened triangle on lateral view (tail of spleen)
- Triangular mass next to left abdominal wall on VD (head of spleen)
What can be seen here?
Splenomegaly
- Generalised splenomegaly is common
- Subjective assessment
- Wide normal range
- There is an overlap maximum physiological/ minimum pathological size
- Spleen enlarges following ACP / barbiturates
What can be seen here?
Splenomegaly
- Localised splenomegaly
- Look for changes in shape as well as size
- Abnormality in the spleen tends to be focal
Discuss ultrasound of the spleen?
- Splenic head lies on the left side, anchored to the stomach by the gastro-splenic ligament
- Fixed position, image from the left flank
- Splenic tail is much more mobile
- Small and usually left sided in the cat
- Larger and extends to ventral midline or even across to the right in the dog
- Image from left / ventral / right as necessary
Discuss appearance of spleen on ultrasound?
- Splenic head is located cranial to the left kidney under the ribs
- – ‘ map of India ’
- Splenic tail is triangular in section and is very mobile
- May contact liver or bladder
- More densely textured than the liver and so generally appears more echogenic
- Capsule is well defined and outline should be smooth
- Vessels (anechoic channels) may be seen entering at the hilus
In a lateral view of a normal dogs abdomen the caudoventral liver edge should be?
Pointed and contained within the costal arch.
What is the correct order of echogenicity in a dogs abdomen?
Spleen> liver > renal cortex.
Discuss stomach radiography?
- Variable amounts of fluid, ingesta and gas within the lumen result in a variable size and shape to the normal stomach
- Rugal folds are often seen as parallel linear soft tissue opacities
- If the stomach is completely collapsed and empty it may not be seen at all
How can gas tell us about position of stomach?
Distribution of gas and fluid depends on the position
What position is this dog in from the position of the gas in it’s stomach?
Right lateral radiograph (fluid in pylorus)
What position is this dog in from the position of the gas in it’s stomach?
Left lateral radiograph (gas in pylorus)
What position is this dog in from the position of the gas in it’s stomach?
DV (gas in fundus)
What position is this dog in from the position of the gas in it’s stomach?
VD view (Fluid in fundus)
What has happened here?
Hiatal hernia highlighted by barium suspension
What has happened here?
Gastric dilation with inherent negative contrast
What has happened here?
Cranial displacement of the stomach due to a small liver
Discuss SI location?
- Pylorus and duodenum are identifiable by location
- Rest of small intestine fills “ the space where there is nothing else!”
Discuss SI opacity?
Pictured normal small intestine
- Cats tend to have less intestinal gas than dogs Cat Dog
Discuss SI size on radiography?
- Roughly even diameter throughout
- Diameter no more than 1.6 x height of L5 vertebral body
What can be seen here?
Here we can see gas in duodenum and pylorus but here the duodenum is all bunched up. This cat had a linear foreign body with had caused it all to bunch up.
What are the pitfalls of asessing SI thickness on a radiograph?
Beware of “ pseudo-thickening ”
- SI (or stomach) wall may appear thickened in plain images with partial filling with gas
Discuss view of the colon and rectum on radiography?
Often easy to identify because they are filled with faeces
- However poor preparation limits interpretation
How does the caecum appear on a radiograph?
When we ultrasound the GI tract what are we looking for?
- Wall thickness
- Presence/absence of wall layering
- Relative layer thickness
- Echogenicity of different layers
- Luminal diameter/contents
- Motility
How does the 5 layered gut wall appear on ultrasound?
Note: 5+5=9 if little lumenal contents
Discuss the ultrasonagraphic appearance of the stomach?
- Contents anechoic- hypoechoic
- Often heterogenous with particles and gas bubbles
- Gas may lead to shadowing deep to near stomach wall
- Peristaltic activity may be apparent
- Wall layers relatively equal thickness (particularly mucosa and muscularis)
Overall wall thickness: •Dog: 2 –5 mm • Cats: 1 –4 mm
Discuss SI appearance on ultrasound?
- Small intestine can be seen in longitudinal and transverse sections with typical layering
- Peristalsis should be seen
- Mucosal layer much thicker than other layers
Wall thickness (jejunum):
Dog: 2.0 -4.7 mm
Cats: 1.5 –3.6 mm
N.B. Duodenum slightly thicker
How does the large intesting appear ultrasonographically?
- Intestinal wall is thinner and the layers more equal
- Loops are significantly larger in diameter
- Slower contractions
- More echogenic contents
- Usually cast an acoustic shadow
How does the abnormal stomach appear ultrasonographically?
Wall thickening
Neoplasia: Typically with:
- Loss of layering pattern
- Decreased echogenicity
Severe gastritis can obscure wall layering:
- Typically hyperechoic mucosa
Foreign body
- May be difficult to identify due to luminal gas
How does the abnormal SI appear ultrasonographically?
Wall thickening
Inflammatory bowel disease
- Typically with preservation, but possibly alteration, of layering pattern (rare to lose)
However
- Wall thickness/layering may be normal
- Changes may be focal or segmental
- Muscularis may be preferentially thickened
- Low-grade lymphoma may have similar appearance in cats
What is loss of layering associated with in the SI?
Loss of layering
- Commonly associated with neoplasia
- In small intestine of dogs loss of layering makes neoplasia 50x more likely than inflammatory disease
- Usually regional lymph nodes enlarged with neoplasia
What can be seen here?
Foreign bodies in SI
What can be seen here?
Intestinal Lesions
- Intussusception
A lesion of the SI wall in a dogs shows thickening and loss of layering on ultrasound exam is likley to be?
Neoplasia
Discuss emergency ultrasonography?
1 diaphragmatic hepatic
2 spleno renal
3 Cysto colic
4 Hepato renal
Summarise radiography and ultrasonography in abdominal imaging?
- Radiography and ultrasonography are complementary in abdominal imaging
- Radiography is particularly useful to evaluate gas and mineralised structures
- Ultrasonography gives good detail of soft tissue architecture
- Ultrasonography is very non-specific, so further diagnostics are usually needed to make a diagnosis
- Ultrasound can be used in an emergency setting to evaluate for free abdominal fluid (AFAST)
