10.1 GI Imaging Flashcards
What x-rays are used to image he GI tract?
Abdominal x-ray AXR
Erect chest x-ray CXR
What contrast studies might be used to view the GI system?
Barium swallow and video fluoroscopy - upper GI tract
Barium enema - distal GI tract
Barium meal/follow through - small intestines
Water soluble contrast studies
What are the 5 modes of imaging the GI system?
Plain x-rays Contrast studies Ultrasounds Cross-sectional imaging (MRI/CT) Angiography
What are the 3 spinal levels we take CT scans of the GI tract at?
T12
L1
L3
Why request an AXR?
Acute abdominal pain
- useful for large bowel obstruction as volvulus show up clearly on abdo X-ray
- not useful for small bowel obstruction
Acute exacerbation of IBD - if suspecting toxic megacolon with perforation
Renal colic - CT first line but abdo xray can be done before surgery to see if stone has passed
How does small bowel obstruction present on a plain abdominal x-ray?
Central position
Often dont see without contrast of gas/air
Plicae circulares on wall - tine lines that cross entire wall
How does an obstructed large bowel appear oN a plain ABX?
Peripheral position - may appear sentrally as the transverse colon can hang down and sigmoid colon can loop and be long
Haustra - lines only extend partially
What are haustra?
Saculations of the large bowel due to the contraction of out longitudinal muscle
What is the first line treatment for small bowel obstruction?
CT scan
Why is CT scan useful to image small bowel obstruction?
Can identify level and cause of the obstruction
Can determine if bowel in strangulated
Why is CT the first line for imaging large bowel obstruction?
Confirm diagnosis
Localise the location of obstruction
Identify the cause
Why might an ABX of the large bowel be useful?
Colonic distension - gaseous secondary to gaseous producing organisms in faeces
Small bowel dilation in incompetence of ileocaecal valve
As LI sits peripherally we may be able to determine level of obstruction due to surrounding features
How wide can a large bowel distend?
6cm
What is the 3 6 9 rule?
The widths regions of bowel can be distended to during obstruction
3cm = small bowel
6cm = large bowel
9cm = caecum
What is a sigmoid volvulus?
Twist at the base of the sigmoid mesentery in the left iliac fossa.
Why is the sigmoid bowel prone to volvulus?
As the sigmoid bowel has its own mesentery. The descending bowel is retroperitoneal and has no mesentery
What is the sigmoid prone to twisting?
Constipation - full of faeces
Sigmoid tumour
How does a sigmoid volvulus appear on an xray?
Large dilated coffee bean appearance
What is toxic megacolon?
Colonic dilatation due to acute deterioration with UC or colitis. Oedema and pseudopolyps.
How does toxic megacolon appear on an xray?
Very dilated large bowel.
Mucosal islands - fluffy lighter patches in the swollen bowel
What is an erect CXR most useful for imaging in the GI tract?
Perforation resulting in pneumoperitoneum
What is pneumoperitoneum?
When air/gas has entered the peritoneal cavity
How is a pneumoperitoneum imaged?
Erect CXR
Dark regions under the diaphragm shows presence of gas in the peritoneal cavity
What might cause perforation of the GI tract?
- Peptic ulcer
- Diverticular
- Tumours within GI tract
- Obstruction
- Trauma
- Iatrogenic
When might gas under the diaphragm in a CXR be an acceptable finding?
Post laparoscopic surgery
Patients are Insufflated with carbon dioxide to expand the visible field for surgeons.
What direction are CXR looking for bowel perforation taken in?
AP direction
What unintentional findings might appear on a ABX?
Stones and calcification (e.g. chronic pancreatitis)
Foreign bodies
What structures can be imaged with a barium swallow?
Pharynx
Oesophagus
Proximal stomach
What is a barium swallow?
Patient swallows barium
Videofluoroscopy to observe the path of the barium
What imaging technique is used to visualise peptic ulcer disease and evaluate haematemesis?
Upper GI endoscopy
What is a barium follow through?
Barium ingested by patient. Wait for barium to travel down to the small intestine before imaging
What is a barium enema?
A tube inserted into the rectum and barium is infused.
Results monitored using fluoroscopy
Can add in another contrast medium (air/CO2) to shoe mucosal problems
What is a barium enema used for?
To image the colon
What are the advantages of using abdominal ultrasound?
Uses sound waves to generate images (not ionising)
Cheap compared to CT and MRI
Portable
Fast scanning
What are the disadvantages of abdominal ultrasound?
Highly user dependent - few people are competent
What can an ultrasound scan of the abdomen be used for?
Imaging gallbladder and gallstones
Stones in bile duct
What structures are seen on a CT scan at spinal level T12?
Aortic hiatus of the diaphragm
Coeliac artery
What structures are seen on a CT scan at spinal level L1?
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) Superior mesenteric artery
What structures are seen on a CT scan at spinal level L3?
Umbilicus
Inferior mesenteric artery
What structures are seen on a CT scan at spinal level L4?
iliac crest
bifurcation of abdominal aorta
What structures are useful for orientation in a CT scan?
RHS = liver
Stomach lies anterior and to RHS of liver
Vena cava lies on posterior border of stomach
Spleen lies posterior to stomach
Why might the right kidney not be seen on a CT scan of T12?
As liver on RHS and displaces right kidney down. Left kidney visible at T12
What structures are visible in a CT of L1 that weren’t visible at T12?
Pancreas Superficial mesenteric artery Right kidney Portal vein Small intestine (very variable)
What structures become visibile at L3 that weren’t at L1?
IVC is separated from the liver
A lot more small intestine (ileum/duodenum)
Colon anteriorly
Psoas muscles
what are MRI used to image?
Soft tissues Tendons Ligaments Spinal cords Brain
What are the advantages of MRI?
No ionisation
Good soft tissue imaging
What are the disadvantages of MRI scan?
Bony structures less detailed than CT
Claustrophobia/anxiety as taken in large tube
Long duration (30 mins)
Loud noises
May be asked to hold breath - difficult for some patients
Unsuitable for patients with metal or certain medical implants
What are the advantages of a CT scan?
Good for imaging trauma, staging cancer, diagnosing conditions in blood vessels
Bony structures and clearer and more detailed
Machine more comfortable than MRI - not fully enclosed
Shorter duration of time than MRI (5-10mins)
Holding breath not required as much
Can be performed with no risks to medical implants or metal
What are the disadvantages of CT scans?
Use ionising radiation
Soft whirring noises and flashing lights may be unsettling ( less so than MRI )
What is GI angiography used for?
A way of visualising the vasculature associated with the intestines
Why has CT angiography replaced conventional angiography for mesenteric vasculature?
As can get a 3D reconstruction from CT scan to get better idea of what’s going on.
Describe the path of the abdominal aorta from the thorax into the abdomen
Initially on the left hand side, travels inferiorly by moving to a more anterior and central position
What pathology can result in an enlarged aortic artery in a CT angiogram?
Abdominal aortic aneurism
Where does the abdominal aorta bifurcate?
At L4 into the common iliac vessels
Where does the IVC sit in relation to the abdominal aorta?
To the RHS
How does the gallbladder present on a CT scan?
A darker circular structure directly beneath the liver on the RHS
What are the 3 branches of the coeliac trunk?
Hepatic artery
Splenic artery
Left gastric artery
