Investigation of the GI tract Flashcards
What types of imaging use radiation?
CT scan
Not USS or MRI - they don’t use radiation
What are the risks of using radiation in CT scans in investigating the GI tract?
Carcinogenesis
Genetic
Risk to foetal development
What are contrast studies used for?
to define hollow viscera typically using barium can be carried out in different ways:
Barium swallow
Barium meal
Barium follow through
Barium enema - barium is inserted rectally allowing visualisation of the colon
When would you use USS to investigate the GI tract?
To determine gallstones
to see if the common bile duct is dilated - gallstone indication
to see the liver and portal vein
to view the appendix
How do USS work?
Use sound waves to generate image at a frequency that humans cannot hear
Cheaper than CT and MRI but downside is that it is highly user dependent (very difficult to carry out and interpret)
What is GI angiography used for?
Bleeding and ischaemia
Visualisation of blood supply to GI tract
How is a GI angiography done?
By injecting radio-opaque contrast agent and taking an x-ray of it
What structures can be seen in an Abdominal x-ray? what are some corresponding abnormalities can therefore be seen?
Stomach small intestine - dilation due to obstruction large intestine - dilation due to obstruction liver spleen kidneys - kidney stones psoas muscles bladder lung bases bones pancreas - chronic pancreatitis aneurysms with calcifications nodes
any part of a hollow tube is visible on an X-ray if it is filled with gas as gas has low density and acts as contrast
most commonly used to visualise the small bowel
What are the two types of cross-sectional imaging?
CT and MRI
Why would you request an abdo x-ray?
Acute abdo pain
Small or large bowel obstruction
Acute IBD exacerbation
Renal colic
Features of small bowel in abdo x ray?
central position with lines going across the whole of the lumen - valvulae connivantes (circular folds)
Feautures of large bowel in abdo x ray?
peripheral position with visible haustra - incomplete lines going across lumen
What is the 3/6/9 rule of bowel obstruction on x ray?
Small bowel is said to be dilated (with gas, due to obstruction) when it’s larger than 3cm
Large bowel is said to be dilated when it is larger than 6cm in diameter
the cecum is said to be dilated it is greater than 9cm
Presentation of small bowel obstruction
Early - vomiting (obstruction is nearer mouth than anus) and mild distension
late - absolute constipation - not even flatus can be passed
colicky pain every 2-3 mins
What can cause small bowel obstruction?
adhesions
hernias - inguinal, femoral, incisonal
tumours
inflammation
Presentation of large bowel obstruction
less frequent colicky pain every 10-15 mins
distension, abdo pain, constipation - early
vomiting - late and can be feaculant
What are the causes of large bowel obstruction?
colorectal adenocaricnoma
diverticular stricture
hernia
volvulus
pseudo-obstruction
What is a volvulus?
When a viscera twists around itself or more commonly when it twists around its mesentery causing the enclosed loop of bowel to dilate and it becomes at risk of perforation or cutting off its blood supply which runs in its mesentery
Where are the most common sites of volvulus in the GI tract?
sigmoid volvulus - most common
cecal volvulus - less common
How can a chest x-ray be useful in investigating the GI tract
Can help diagnose a perforated bowel
What can a perforated bowel be caused by?
peptic ulcer diverticular disease tumour obstruction trauma iatrogenic
What does the chest x-ray have to be erect?
patient needs to sit up for 10 minutes before taking the x-ray because you are looking for diaphragm elevation away from any other viscera by presence of air in the peritoneal cavity and you need to give time for this air to rise before taking the x-ray
the peritoneal cavity normally only contains a very small amount of fluid so the presence of air is abnormal and could help suggest a perforated bowel
Why would you choose to do an abdo CT vs. MRI
CT has good spatial resolution
MRI is time consuming
Why would you choose to MRI instead of CT
doesn’t use radiation
better contrast resolution
How would you visualise the gallbladder and biliary tree?
using magnetic resonance cholangio-pancreatogram - MRCP - specific type of MRI
