S10: GI imaging Flashcards
List different imaging available for the GI system
X-rays: abdominal x-ray and erect chest x-ray
Contrast studies: barium swallow, barium enema, barium meal/follow through & water-soluble contrast studies
Ultrasound
Cross sectional imaging: computed tomography, magnetic resonance imaging
List the common reasons for requesting a plain abdominal radiograph
Determining bowel obstruction
Flare ups of IBD
Compare and contrast the appearance of small and large bowel on an abdominal radiograph
Small bowel – occupy a central position and have lines (valvulae conniventes) that cross the entire bowel wall
Large bowel – occupy a peripheral position and have incomplete lines (haustra) across the bowel wall (faeces can be visible due to slow transit time of the large bowel)
What is first line imaging for small bowel obstruction?
CT scan – can identify the level and cause of the obstruction
Also good at helping to determine whether bowel is strangulated
Do not use plain abdominal radiographs unless CT unavailable
Describe how small bowel obstruction looks on an x-ray
Central position of gas-filled and distended loops of bowel
The white lines passing across the full width of the bowel are ‘valvulae conniventes’ = only found in the small bowel
What is the first line imaging for large bowel obstruction?
CT scan
Not only able to confirm the diagnosis and localise the location of obstruction, but in most instances is also able to identify the cause
Describe how large bowel obstruction looks on x-ray
Colonic distension: gaseous secondary to gas-producing organisms in faeces
Small bowel dilatation which depends on duration of obstruction & incompetence of the ileocaecal valve
Describe how a sigmoid volvulus looks on x-ray
Coffee bean sign – twist at the base of the sigmoid mesentery which is in a fixed position in the left iliac fossa
Describe how toxic megacolon looks on x-ray
Acute deterioration with UC or colitis Colonic dilatation Oedema Pseudopolyps Extensive ‘mucosal islands’ – indicating bowel wall inflammation
Describe perforation on an erect chest x-ray
Causes: peptic ulcer, diverticular, tumour, obstruction, trauma & iatrogenic
An erect chest x-ray can show a very small volume of free abdominal gas – reference to clinical setting is required to determine if this a potentially life-threatening perforation (pneumoperitoneum)
Undergone laparoscopic surgery earlier in the day – free gas under diaphragm is insufflated CO2 = acceptable post-surgical finding
Describe barium swallow
Dedicated test of the pharynx, oesophagus and proximal stomach
Upper GI endoscopy has largely replaced the barium swallow
Give patient barium to swallow & use videofluoroscopy = continuous x-ray which is viewed in real time on a screen
Describe barium enema
Tube inserted into rectum
Barium is then administered, and the results are monitored using fluoroscopy
If mucosal problems are suspected - adding another contrast medium (air/CO2) will help
Largely superseded by CT
Describe abdominal ultrasound
Use of sound waves to generate image – frequency above audible range of human hearing
Cheap compared to CT and MRI
Portable
Highly user dependent
Commonly used to visualise the biliary tree (gallstones and dilated bile ducts)
List features at various spinal levels seen on CT
T12 – aortic hiatus of the diaphragm
L1 (transpyloric) – fundus of gallbladder, pylorus of stomach, neck of pancreas, superior mesenteric artery origin, hilum of kidneys (left is above and right is below)
L3 – umbilicus, inferior mesenteric artery
L4 – iliac crest, bifurcation of abdominal aorta
Describe abdominal MRI
Detailed and high contrast images of the abdomen without using any radiation
Very time-consuming process
Can also be used with contrast to enhance images
