8.1 Imaging of the GIT Flashcards
Give 4 Imaging modalities of the GIT
1) Plain X-rays
- abdominal x-ray (AXR)
- erect chest x-ray (CXR)
2) Contrast studies
- barium swallow
- barium enema
- barium meal/follow through
- water soluble contrast studies
3) Ultrasound
4) Cross-sectional imaging
- computed tomography (CT)
- magnetic Resonance Imaging (MRI)
- angiography
State what the following colours on a X-ray would indicate
- Black
- Dark grey
- Light grey
- White
- Bright white
Black: air ags
Dark grey: fat
Light Grey: soft tissue/fluid
White: bone and calcified structures
Bright white: metal
List the 6 things included on an AXR Checklist
- Patient Identification
- Clinical status
- Patient mobility
- Patient location and travel details
- Indications
- Contraindications
Give 4 reasons why you may order AXR
- Acute abdominal pain - debatable
- Small or large bowel obstruction
- Acute exacerbation of IBD
- Foreign body detection
- Small print indications: rule out rarer conditions
Renal colic… CT now first line investigation
Give 4 clinical signs that may indicate the need for an AXR
- absence/ abnormal bowel sounds
- vomiting
- not passing bowel/wind
- abdominal distension
Why MUST we do an abdominal X-ray for UC flare ups?
To rule out Toxic Megacolon!!
List the steps required to interpret AXR (8)
1) Identify the image and when it was taken: top right corner
2) Identify the patient: full name, sex, DOB
3) Technical adequacy: views and quality (is it a good X-ray?)
4) Artefacts and foreign bodies: eg. clinical insertions, piercings
5) GI Tract and bowel gas patterns: identify if these look normal
6) Solid organs: kidneys are often visible
7) Aorta and vessels: aneurysm, calcification of vessels
8) Muscles and bone
What is meant by technical adequacy?
Orientation: check for R and L markers
Field: are both hemi-diaphragms present, are R and L hip joints present
Penetration: can the outlines of bones and vertical bodies be seen
List 4 foreign bodies that may be present in an AXR
External artefacts
Surgical artefacts
Foreign bodies
- Oral/nasal route
- Rectal route
- Urethral route
- Vaginal route
Will a lying down X-ray of the abdomen show fluid or gas?
NO this is will not, an erect AXR is better
List when a hollow tube will be visible and when will it not be
Gas filled or Gas and Fluid filled
Low density gas acts as a contrast
Fully fluid filled NOT visible
What features of the small intestine should be visible on an AXR
Valvulae conniventes (also known as plicae circularis). These are mucosal folds of the SI seen as a thin line that spans aross the entire wall
What features of the large intestine should be visible on an AXR
Haustra: these don’t span the entire width of the intestinal wall (diamter of around 6cm is normal)
Faeces and gas are very often present
Remember
- T colon can hang down to pelvis
- S colon can loop and be long
The large bowel also tends to have a straight course compared to the SI which has a tortous appearance
Give 5 abnormal gas patterns to recognise
- Small bowel obstruction (>3 cm)
- Large bowel obstruction (>6 cm)
- Paralytic Ileus
- Volvulus
- Toxic Megacolon
Give 6 causes of a small bowel obstruction
- Post operative (most common)
- Tumours
- Crohn’s disease
- Adhesions
- Hernias (Inguinal, Femoral, Incisional)
- Inflammation
Describe what would be seen in a small bowel obstruction
- bowel looks more closely folded in the centre, so appearance becomes more tortous
- extremly swollen, will be greater than 3cm
- valvulae conniventes line is still visible entire way across (may not always be visible due to gas patterns)
- It will ONLY be full of gas (build up due to an obstruction)
- no faeces will be visible
- described as “meandering lengthy loops” (visible long, slow, bends)
Give 4 common presentations of a small bowel obstruction
1) Vomiting (early)
2) Distension (mild)
3) Absolute constipation (late)
4) Colicky pain
What would be seen on a large bowel obstruction?
- peripheral location
- haustra can still be seen
- bowel visually looks bigger, greater than 6cm
- lumen contains faces
- rectum is roughly still centred in the pelvis as it descends
Give 4 common presentations of a large bowel obstrution
Vomiting (late, faeculant)
Distension (significant)
Pain
Absolute constipation
Give 6 causes of a large bowel obstruction
- Colorectal carcinoma
- Diverticular stricture
- Hernia
- Volvulus
- Pseudo-obstruction
What is a Volvus
Torsion of the bowel, occurs most commonly in sigmoid colon of constipated elderly patient. Can occur in caecum known as a “caecal volvulus” but is uncommon
Results in twisting around mesentery causing the enclosed bowel loop to dilate
Surgical emergency due to risk of perforation and risk of Ischaemia
Describe where a sigmoid volvulus would start?
What is the classic sign seen on an AXR
Starts in LIF and obstruction causes dilatation of proximal bowel
Classic coffee bean sign towards RUQ,
How could you differentiate a Sigmoid Volvulus from a Caecal Volvulus on an AXR
The classic coffee bean sign points to the RUQ in a Sigmoid Volvulus but will point in a different direction in a Caecal Volvulus
Remember: Caecal Volvulus is RARE
What is Toxic Megacolon associated with and what is its classical AXR sign?
What is the biggest risk of these?
Caused by acute deterioration with UC or Colitis
Results in colonic dilatation seen as a Thumb-printing sign
Huge risk of porforation which can be extremly dangerous
Give 6 examples of soft issues
Organs
- liver
- spleen
- kidneys
- bladder
- lung bases
Musculature
Bones
- pelvis
- sacrum
- coccyx
- lumbar spine
- lower thoracic spine
- lower ribs
When is the bladder visible on an xray?
How would you identify the kidneys on an x-ray and why is this helpful?
Bladder is only visible if it is full
Kidney’s can be identified by following up the lateral psoas muscle margin that drags diagonally from the upper lumbar vertebral bodies to the lesser femoral trochanter on each sides
By being able to identify the kidney then if we see an object that is shiny and bright in that area that shouldn’t be we can think differentials such as “is this a renal/kidney stone/ renal calculi”
If a Renal calculi is causing obstruction what would be seen on an X-ray?
Causes a build up of Air within the kidney (black) on an X-ray
What is a Staghorn calculi?
Branched stones that fills all or part of the renal pelvis and branch into several or all of the calyces.
Most often composed of struvite, but frequently contain Ca2+
What is the most likly foreign body seen on this X-ray?
How can we be sure this object is correctly placed?
NG chest tube : usually put in to rest the stomach and the intestine to drain them so they don’t have to continue working which may worsen a bowel obstruction
We can tell an NG tube is in the stomach by taking some fluid up and testing it using litmus paper
Perforation can lead to pneumoperitoneum, what is this and what would be seen on X-ray?
Abnormal presence of air or other gas in the peritoneal cavity
Seen on an Erect chest X-ray as a crescent moon sign above the diaphragm: due to a lung cavity that is filled with air and has a round radiopaque mass
Give 4 causes of a pneumoperitoneum
- Peptic ulcer
- Diverticular
- Tumour
- Obstruction
- Trauma
- Iatrogenic (3-6/days after a laproscopy)
What are the 6 features on the Fluoroscopy Checklist?
1) Patient Identification
2) Clinical status
3) Patient mobility
4) Patient location and travel details
5) Indications
6) Contraindications
To interpret a a Fluroscopy what steps must you take?
1) Identify the image and when it was taken
2) Identify the patient
3) Full name, sex, DOB
4) Technical adequacy
5) Artefacts and foreign bodies
6) Identify normal anatomy
7) Any pathology
In a contrast study what type of contrast would you use to define hollow viscera?
Barium
Water soluble
Give 4 common GI contrast studies
1) barium swallow (ensdoscopy)
2) barium meal (endoscopy) - not as often used
3) small bowel enema/Follow through (MRI)
4) enema (CT)
In a Barium swallow contrast study, what would an “apple core sign indicate”?
What does the image below show?
Apple core sign is most frequently associated with constriction of the lumen of the colon by a stenosing annular colorectal carcinoma
This image shows an oesophageal stricture due to something compressing it, causing narrowing of the oesophageal lumen
What does this barium enema show?
What is this?
Image shows diverticula: enema has highlighted the multiple out-pouches throughout the GI tract
Diverticula: are small, bulging pouches that can form in the lining of your digestive system (seen in diverticular disease), can become inflammed and progress to diverticulitis
What does CT stand for?
Computerised Tomography
What are the 8 features on the CT Checklist?
Same as Fluroscopy + renal Function and contrast agent reactions
These are added to ensure the contrast we use doesn’t cause acute kidney injury or renal damage
How do you interpret a CT?
1) Identify the image and when it was taken
2) Identify the patient
3) Full name, sex, DOB
4) The Scout view (normally bottom left, aims to orientate you to where abouts in the body you are)
5) Precontrast view
6) Post Contrast view
7) Windowing for dedicated organ assessment
* allow us to look at a particular organ (based on the different densities of absorption of the contrast by the CT scan
How is contrast administered in an abdominal CT?
What the biggest downside to these?
Compare these to an MRI
IV or oral/rectal contrast
Biggest NEGATIVE: High dose radiation
Compared to an MRI there is Good spatial resolution BUT poor contrast resolution
Make sure you understand this CT
When would using a Virtual Colonoscopy be useful?
Good for people with low tolerance of a normal colonoscopy
What are the 6 features on the MRI Checklist?
What is a MASSIVE Contraindication for MRI’s?
Same as Fluoroscopy
Contraindications = METALS
- Pacemaker
- defibrillator
- hearing aid
- cochlear implant
What are the steps to interpret an MRI?
1) Identify the image and when it was taken
2) Identify the patient: Full name, sex, DOB
3) Identify sequence: which tissues we are looking at
* T1 and T2 each show various tissues better
4) Identify key structures with respect to signal intensity
5) Assess for pathology, aberrant anatomy and physiology
When would you use T1 vs T2 on an MRI?
What would various colour indicate on each?
Deciding whether to use T1 or T2 is usually dependant on what you’re looking for:
T1: better for organs
- white: fatty tissue
- light/mid grey:rgans and soft tissue structures
- dark grey/black: air, bone/ligaments/ tendons/ stones/ fast flowing blood
T2: better for proteins, abscesses, infections or collections
- white: high free water tissue, oedema, protein tissue, fatty tissue
- light/mid grey: organs and soft tissue structures
- dark grey/black: air, bone/ligaments/ tendons/ stones/ fast flowing
- blood
BUT whether T1 or T2 is used is highly dependant on the machine being used and the radiologist’s choice
What does MRI stand for?
Give 2 positives of Abdominal MRIs and one negative
Magnetic resonance imaging
Positives:
- No radiation
- Good spatial and contrast resolution
Negative: Time consuming
What does MRCP stand for and what may it be useful in identifying?
Magnetic resonance cholangiopancreatogram: extremely useful in identifying the gallbladder and bilary tree for problems or obstructions
What are the 7 features on an abdominal Ultrasound checklist?
Same as Fluroscopy + Full Urinary bladder (MUST BE FULL)
How would you interpret an abdominal Ultrasound?
1) Identify the image and when it was taken
2) dentify the patient: Full name, sex, DOB
3) Identify Liver, Gall Bladder, CBD, Pancreas, spleen, kidneys
How does an abdominal US work?
Give 2 positives and one negative
Use of sound waves to generate image (frequency above audible range of human hearing)
Positives:
- cheap compared to CT and MRI
- portable
Negative: Highly user dependant
Gallbladders are said to be “hyperchoic” what does this mean?
How would you differentiate gallstones from polyps?
Gallstones are what we call hyperechoic meaning they reflect back things (lots of echos). They are also gravity dependant in the gallbladder so we must know what position we are in.
The ones that move around during imaging tend to be gallstones (because they are gravity dependant)
Ones that remain stationary tend to be polyps within the gallbladder wall
When may a GI Angiography be used?
Identify what each of the images below shows
Used to evaluate vascular trauma
Image one is a normal angiogram
Image two is an AAA
Image three is a dissection
