Session 10: Imaging of the Gastrointestinal Tract Flashcards
Imaging modalities of GI tract.
Abdominal x-ray
Erect chest x-ray
Barium swallow
Barium enem
Barium meal
Water soluble contrast
Ultrasound
CT
MRI
PET-CT
Angiography
What gives the highest dose of radiation?
CT abdo/pelvis
Risks of imaging of GI tract.
Carcinogenesis
Genetics
Developmental risks to foetus
Why would an AXR be requested?
Acute abdominal pain
Small or large bowel obstruction
Acute exacerbation of IBD like flare-ups
Renal colic is now done by CT
Systemic approach for an AXR.
ABDO X
Air/gas
Bowel
Dense structures (calcifications and bones)
Organs and soft tissue like liver, spleen and kidneys
eXternal objects and artifacts
How will small bowel present on an AXR?
Central position and have lines (valvulae conniventes) that cross the entire bowel wall.
How will large bowel present on an AXR?
Peripheral position and have incomplete lines (haustra).
Faeces can be visible due to the slow transit time of large bowel.
Give examples of abnormal gas patterns to recognise.
Rules of 3s (3,6,9)
Small bowel obstruction (>3 cm)
Large bowel obstruction (>6 cm)
Competent ileocaecal valve (>9 cm)
Incompetent ileocaecal valve (<9 cm)
Paralytic ileus
Volvulus
Toxic megacolon
Causes of small bowel obstrution.
Adhesions
Hernias
Tumours
Inflammation
Causes of large bowel obstruction.
Colorectal carcinoma
Diverticular stricture
Hernia
Volvulus
Pseudo-obstruction
How might sigmoid volvulus present on AXR?
Large coffee bean sign starting in the LIF and pointing towards RUQ.
What is this?
Colonic dilation
Oedema
Pseduopolyps
Toxic megacolon
What is this?
Called lead pipe colon where there is a featureless colon with the loss of haustra.
It is due to Ulcerative colitis
Renal calculi
Chronic pancreatitis
Vascular calcification
Abdominal aortic aneurysm
Foreign bodies
Why might an erect chest x-ray be ordered?
In case of bowel perforation
Give causes of bowel perforation
Peptic ulcer
Diverticular
Tumour
Obstruction
Trauma
Iatrogenic
How will bowel perforation show up on an erect chest x-ray?
It will show free gas right under the diaphragm.
What is used to define hollow viscera?
Barium contrast and water soluble contrast.
Give the common GI contrast studies.
Swallow
Meal
Follow through
Enema
What does a swallow test show?
It can highlight problems and anatomical variances found with the stages of swallowing.
What does a follow through show?
Allows contrast to pass into the small intestine and can show any variances or pathology in small intestines.
Meal barium shows the stomach
What does a contrast enema show?
Allows the large intestine to be highlighted
Why might a CT be used?
To produce a high resolution image of the abdomen that can be further augmented with contrast to show any pathology not visible on x-ray.
However it comes iwth a cost of high dose radiation.
What is virtual colonoscopy?
Individual images from a CT scan that can be reformatted and combined to produce a 3D representation of the scanned anatomy.
Why might an MRI be used?
To give a detailed and high contrast image of the abdomen without radiation. It can be enhanced by contrast.
It is however very time consuming.
Why might abdominal USS be used?
Cheap and portable method.
It is user dependant however and you might miss pathology.
What is abdominal USS often used for?
To visualise the biliary tree to see gallstones and dilated bile ducts.
Why are AXRs not used as much any more?
Because they are not very sensitive and not very specific.
A lot of radiologist gets it wrong 30-40% of the time.
