Imaging of gastrointestinal disease Flashcards by Sophie Robinson

Describe how the normal pancreas appears on radiography, where is it located?

Normal pancreas is not observed on plain radiographs
Medial to duodenum, between gastric body and transverse colon, medial to spleen and cranial to left kidney

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Which imaging modality is best for visualisation of the pancreas?

Ultrasound

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Describe pancreatic enlargement and how it appears on radiography

Pancreatitis or neoplasia
Mass effect: Lateral displacement of the duodenum and caudal displacement of the transverse colon
Increased ST opacity in the craniodorsal to mid abdomen caudal to fundus
Localized loss of serosal detail (focal fluid/peritonitis)

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Describe the normal oesophagus on radiography

On a plain radiograph not clearly delineated unless gas filled.
Midline structure within the mediastinum
A small amount of gaseous dilation is normal (sedation related).
Fluoroscopy essential

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Describe a megaoesophagus and how it presents on radiography

Segmental or generalised dilation
May cause ventral deviation of the trachea and widening of the mediastinum.
Tracheo-oesophageal stripe sign
(summation of tracheal wall and oesophageal wall).

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Where are the predilection sites for an oesophageal foreign body?

Thoracic inlet
Heart base
Cranial to the diaphragm/cardia

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Which contrast media is contraindicated with suspected oesophageal perforation? Which can be used?

Barium
Use endoscopy or non-ionic, iodine containing contrast

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Where would gas/material leak if the (thoracic) oesophagus was perforated?

Mediastinum – seen on the D/V view

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Where does gas move within a hollow viscus (e.g. stomach, intestine, etc)?

Non-dependent side

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How is positional radiography used in gas distribution?

Right and left lateral view and VD ± DV

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Where do we expect the gas within the stomach based on the radiographic view?

Right lateral view: Fundus.
Left lateral view: Body/pyloric antrum.
Ventrodorsal view: Body (superimposed over the vertebral column).
Dorsoventral view: Fundus (left cranial quadrant).

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Why are contrast studies less used now?

Time consuming, cost intensive and low diagnostic yield
Superseded by combining radiography with ultrasound instead
They are only useful, if carried out properly

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Where does the normal stomach lie

Positioned within the costal arch in the cranial abdomen, directly caudal to the liver.

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Name the compartments of the stomach

Cardia
Fundus
Body
Pyloric antrum/pylorus

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Do not mistake a fluid filled pyloric antrum with..?

A mass

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Name the 5 layers of the stomach from the outside in

Serosa
Muscularis
Submucosa
Mucosa
Lumen

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Which layers of the stomach are hyperechoic (dark)?

Muscularis and mucosa

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Rugal folds are visible in which parts of the stomach

Fundus
Body

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Describe how gastric dilation presents on radiography

Gas opacity in fundus/body: very “dark” = large volume of gas

What are the two causes of fluid and gas dilation of the stomach

Pyloric outflow obstruction
Function ileus

What are the two causes of just gas dilation of the stomach

Aerophagia
GD/GDV

How does a fluid and gas dilation of the stomach present on radiography?

Mostly soft tissue opacity with a faint gas opacity “bubble” floating on top

How are stomach foreign bodies assessed on radiography

Easy to identify if of mineral/metallic opacity.
Remember orthogonal views are necessary to confirm location.
Gas may be trapped in textile or botanical FB or toys resulting is bizarre gas patterns.
May cause partial or complete obstruction

What is gastric dilation and volvulus?

Life threatening disease!
Marked gas dilation and rotation around the longitudinal axis

Describe how the stomach rotates in GDV

- Pylorus shifts dorsally, cranially, and to the left - Body shifts toward the right - Fundus usually is displaced ventrally and to the right - Spleen follows the greater curvature toward the right (gastrosplenic ligament)

How does GDV present on radiography?

- Marked gas dilation and displacement of gastric compartments - Fundus displaced caudoventrally and right. - Pyloric antrum displaced craniodorsal and left. - Compartmentalisation with a dividing soft tissue band (“shelf”). - Mass effect on other abdominal organs

Describe the normal radiographic appearance of the SI

- Normally soft tissue opacity band/tube or as circular/ovoid ST opacity when viewed end-on - Some homogeneous gas-filling is normal in dogs - Little to no gas filling in cats

Describe the 'wall thickness illusion' of the small intestine

- Wall thickness cannot be reliably assessed on plain radiographs - “Wall” is summation of true wall and intestinal luminal fluid - Fluid and soft tissue indistinguishable on radiographs - Requires contrast (to mix with fluid) or ultrasonography - Not much fluid, approximates wall thickness

Which layer of the small intestine is the thickest?

Submucosa

Which area of the small intestine has the thickest wall?

Duodenum

Which layer of the small intestine is thicker in the ileum? How does this appear on US?

The submucosa is thicker in the ileum and flower-like/wheel-like appearance on transverse images

List the causes of small intestinal dilation

Mechanical obstruction: - Foreign body - Tumour Functional ileus: - Severe inflammation - Toxic - Stress

Define ileus

Failure of the intestinal contents to pass normally Can be fluid or gas dilation

No one loop of small intestine should be more than ... the diameter of any other loops

Describe how an obstruction in the small intestine leads to an obstructive pattern seen on radiography

- Fluid and/or gas dilation proximal to the obstruction. - Creates “two populations of intestine” around the obstruction -> one abnormal proximal -> one normal distal population to obstruction May not see two population if the obstruction is very proximal or very distal!

Once a FB makes it passed which point of the GIT do you not longer have to worry about it?

Colon

Describe how a small intestinal obstruction presents on ultrasound

Secondary changes depending on level of obstruction: - Fluid dilation proximal to FB and to-and-fro movement - Normal intestines distal to the obstruction (two populations)

How does a small intestinal FB present on ultrasound?

Hyperechoic, irregular or artificially symmetrical shape Usually strong distal shadowing

Describe linear foreign bodies and the effect they have on the GIT

Commonly seen in cats Plication/hair-pin bends, bunching Cause telescoping of the SI onto the FB +/- localised peritonitis (loss of serosal detail, streaky appearance

Describe intussusception and how it appears on radiography

Most commonly in young dogs and cats, in older patients usually secondary to other pathology - Ovoid/elongated ST mass/dilation - Possibly crescent shaped gas opacity between intussusceptum (inner) and intussuscipiens (outer) - No “normal” caecal gas, shortened colon (ileocolic int.)

Describe how intussusception appears on ultrasound

- Easily diagnosed on ultrasound - Onion ring/bullseye appearance on transverse images - Intestinal walls identified within intestinal lumen - Also vessels/blood flow within the lumen

How is small intestinal neoplasia diagnosed using imaging

- Difficult to identify, need to be of substantial size - Signs secondary to obstruction may be seen - Care not to overinterpret “apparent wall thickening” - Localised masses, irregular gas filling/contrast column - US very useful

How would a small intestinal neoplasia appear on ultrasound?

Loss of wall layering May have central gas containing lumen (distal shadowing) May see signs of obstruction

Where is the caecum located normally?

In right dorsal aspect of abdominal cavity, often level of the left kidney (on a lateral radiograph)

How does the normal caecum appear on radiography?

- In cats is small, rarely contains gas and normally not visible or comma shaped - In dogs appears as a semicircular, snail-shell gas filled structure

The colon is divided into which 3 sections?

Ascending, transverse, and descending colon