Lecture 19– imaging of the GI tract Flashcards
Imaging available for GI system
- Plain X-rays
- Abdominal x-ray (AXR)
- Erect chest x-ray (CXR)
- Contrast studies
- Barium swallow/enema
- Barium meal/follow through
- Water soluble contrast studies
- US
- Cross- sectional imaging
- Computed tomography
- Magnetic resonance imaging (MRI)
- Angiography
AXR is …….. utilised as a first line investigation
less
when is AXR used vs CT scan in relation to small or large bowel obstruction
- CT scan is first for small bowel obstruction
- Abdo x-ray may show volvulus in large bowel obstruction
first line investigation for renal colic
CT
- abdo Xray can be done to check stone ahs passed
AXR and Acute exacerbation of IBD?
Potentially useful for toxic megacolon with perforation
presentation of small bowel obstriction on X-ray
- Central position
- Often don’t see (need gas in the bowel to see)
- Plica/circulares/ permanent folds/ Valvulae conniventes
- Cross the entire wall
- Thin
which rule applies for large boewl obstruction
369
The 3-6-9 rule is a simple aide-memoire describing the normal bowel calibre:
small bowel: <3 cm
large bowel: <6 cm
appendix: <6 mm
caecum: <9 cm
presentation of large bpewl obstruction
- Peripheral position
- Haustra- sacculation’s formed by outer longitudinal muscles
- Lines only extend partially along the bowel wall
- Remember
- Transverse colon hands down to the pelvic
- Sigmoid colon can loop and be long
example cause: diverticular stricture
Ct and small bowel obstruction
- CT = first line of imaging
- Can identify the level and cause of obstruction
- Also good helping to determine whether bowel is strangulated
- Do not use plain abdominal radiographs unless CT unavailable
why is CT most widley used method in large bowel obstruction
- Localise location of obstruction but in most instances also identify causes
sigmoidal volvulus is said to look like a
coffee bean
- Due to a twist at the base of the sigmoid mesentery which is in a fixed position (*) in the left iliac fossa
- This results in the appearance of a giant coffee bean, the typical sign of sigmoid volvulus
toxic megacolon can be caused by
- Acute deterioration with UC or colitis
- patient will be unwell
Toxic megacolon- X-ray
- Colonic dilatation
- Oedema
- Pseudopolyps
erect CXr will be in
AP
- cant get accurate reading o heart side
what may you need an erect chest X-ray for inr regards to the GI system
Pneumoperitoneum
- An erect chest x-ray can show even a very small volume of abdominal gas
- Reference to the clinical setting is required to determine if this a life threating perforation
- A careful check should be made for free gas under the diaphragm on every chest X-ray
iatrogenic causes of penumoperitoneum
- Patient might have undergone laparoscopic surgery earlier in the day free gas under diaphragm is insufflated CO2- an acceptable post surgery finding
- Causes of pneumoperitoneum
perforation due to
- Peptic ulcer
- Diverticular
- Tumour
- Obstruction
- Trauma
- Iatrogenic
x-rays are also useful in looking for
- stones and calcificatione e.g. in chronic pancreatitis
- foregein bodies
barium swallow is a dedicated test of the
pharynx, oesophagus and proximal stomach
- You give pt barium to swallow then use video fluoroscopy (which is a continuous X-ray which is view in Realtime on a screen)
what has largely replaced barium swallow for the assessemnt of peptic ulcer disease and elevation haematemesis
Upper GI endoscopy has largely replaced barium swallow for the assessment of peptic ulcer disease and elevation of haematemesis
Barium follow-through
- Following a barium swallow, we can wait for the barium to reach the small intestine
- Therefore can be used to image small intestine (endoscopy cannot reach here)
barium enema
- Tube inserted into rectum
- Administered and results monitored by fluoroscopy
- If mucosal problems are suspected then adding another contrast medium (air or CO2) will help
- Largely superseded by CT
- Used to visualise:
- Strictures
- Mucosal problems (with air or CO2)
CT shows UC
abdominal ultrasound uses
- Use of sound waves to generate image
- Frequency above audible range of human hearing (20 KHz)
- Usually 2-18 MHz)
pros and cons of abdominal ultrasound
- Pros
- Cheap compared to CT and MRI
- Portable
- Cons
- Highly user dependent
CT scan show different features at
various spinal levels
lets orientate ourselves- The CT is as if we are standing
As if we were standing at the persons feet
- On the right
- The liver
CT-T12 will visualise the
- Aortic hiatus of the diaphragm
- When celiac drunk is given off
CT L1 (transpyloric plane) will visualise the
L1- Midgut
- Also known as transpyloric plane
- Fundus of the gallbladder
- Pylorus of stomach
- Neck of pancreas
- Superior mesenteric artery origin
- Hilum of kidneys
- Left: above
- Right : below
- Dark area on the stomach= gas can see fluid level of the stomach
CT L3 will visualise the
L3- Hindgut
- Umbilicus
- Bottom of liver
- Can see more SI
- Inferior mesenteric artery
CT L4
L4
- Iliac crest
- Bifurcation of abdominal aorta
MRI pros and cons
- Pros
- No radiation (magnetic fields)
- Soft tissues, tendons and the brain
- Cons
- Not applicable for those with metal implants
- Very claustrophobic
- Takes longer
what are MRI vs CT scan used to visualise
MRI- looking at soft itsuse,s tnedons, ligaments, spinal cords and the brain
CT- imaging injuries from truama, staging cancer and diagnosing conditions of blood vessels
bony sturctures more or less clear in MRI than CT
less clear
MRi powered by
storng magentic filed
CT powered by low dose radiation
what takes longer MRI or CT
MRI (30 mins) vs 5-10min CT
what must we beware of with MRI scan
pts with metal or certain emdical impalnts cannot undergo MRI due to magentic field pulses
Abdominal MRI anatomy
GI angiography
- A ways of visualising the vasculature associated the intestines
- CT angiography has replaced conventional angiography for mesenteric vasculature
- Can get a 3D reconstruction
celiac trunk found at
T12
celeiac drunk splits into
- Left- splenic artery and left gastric
- Right – common hepatic artery
- Superior mesenteric artery at
- L1
- Branches
branches of superior mesenteric
- middle colic
- right colic
- illeocolic
- illeo and jejunal branches
- Inferior mesenteric artery at
- L3
- Goes off slightly to the left and drops into the pelvis without branching –> superior rectal artery
branches of the infeiror emsenteric
left colic
sigmoid
superior rectal
