Investigation of the GI tract

Question 1

What types of imaging use radiation?

Answer 1

CT scan

Not USS or MRI - they don’t use radiation

Question 2

What are the risks of using radiation in CT scans in investigating the GI tract?

Answer 2

Carcinogenesis
Genetic
Risk to foetal development

Question 3

What are contrast studies used for?

Answer 3

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

Question 4

When would you use USS to investigate the GI tract?

Answer 4

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

Question 5

How do USS work?

Answer 5

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)

Question 6

What is GI angiography used for?

Answer 6

Bleeding and ischaemia

Visualisation of blood supply to GI tract

Question 7

How is a GI angiography done?

Answer 7

By injecting radio-opaque contrast agent and taking an x-ray of it

Question 8

What structures can be seen in an Abdominal x-ray? what are some corresponding abnormalities can therefore be seen?

Answer 8

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

Question 9

What are the two types of cross-sectional imaging?

Answer 9

CT and MRI

Question 10

Why would you request an abdo x-ray?

Answer 10

Acute abdo pain

Small or large bowel obstruction

Acute IBD exacerbation

Renal colic

Question 11

Features of small bowel in abdo x ray?

Answer 11

central position with lines going across the whole of the lumen - valvulae connivantes (circular folds)

Question 12

Feautures of large bowel in abdo x ray?

Answer 12

peripheral position with visible haustra - incomplete lines going across lumen

Question 13

What is the 3/6/9 rule of bowel obstruction on x ray?

Answer 13

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

Question 14

Presentation of small bowel obstruction

Answer 14

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

Question 15

What can cause small bowel obstruction?

Answer 15

adhesions

hernias - inguinal, femoral, incisonal

tumours

inflammation

Question 16

Presentation of large bowel obstruction

Answer 16

less frequent colicky pain every 10-15 mins

distension, abdo pain, constipation - early
vomiting - late and can be feaculant

Question 17

What are the causes of large bowel obstruction?

Answer 17

colorectal adenocaricnoma

diverticular stricture

hernia

volvulus

pseudo-obstruction

Question 18

What is a volvulus?

Answer 18

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

Question 19

Where are the most common sites of volvulus in the GI tract?

Answer 19

sigmoid volvulus - most common

cecal volvulus - less common

Question 20

How can a chest x-ray be useful in investigating the GI tract

Answer 20

Can help diagnose a perforated bowel

Question 21

What can a perforated bowel be caused by?

Answer 21

peptic ulcer
diverticular disease 
tumour 
obstruction
trauma 
iatrogenic

Question 22

What does the chest x-ray have to be erect?

Answer 22

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

Question 23

Why would you choose to do an abdo CT vs. MRI

Answer 23

CT has good spatial resolution

MRI is time consuming

Question 24

Why would you choose to MRI instead of CT

Answer 24

doesn’t use radiation

better contrast resolution

Question 25

How would you visualise the gallbladder and biliary tree?

Answer 25

using magnetic resonance cholangio-pancreatogram - MRCP - specific type of MRI