advanced bowel imaging Flashcards
CT Colonography what is it?
A specific CT examination used to evaluate the large bowel.
Undertaken by introducing air into the prepared bowel.
Laxative, gastrografin and diet preparation for full study
Diet preparation only for ‘faecal tagging’.
Clinical Indications
Colonic cancer follow up
Polyps investigation
Abdominal Pain
Changing in Bowel Habits (CIBH)
Weight loss
Iron-deficient anaemia (IDA)
Colorectal cancer screening
Failed colonoscopy
Bowel Cancer Screening
procedure of colonography
48/24 hours prior to appt low residue diet at home
Take Gastrografin as instructed mixed with water
Take all other medication (except a few contraindicated drugs)
Day of the scan DO NOT have breakfast ONLY drink clear liquids
Once at appt
Change into gown – all clothes off except underpants
ID check undertaken, IV safety questionnaire, buscopan safety questionnaire, cannulated, procedure explained, consent forms signed
In the room, Radiographers introduce themselves, check all forms and inject IV buscopan if suitable
Patient lays on their left side facing away from the air insufflator
Tube inserted into the back passage, balloon inflated to hold in place and CO2 turned on
Once at 4 liters, lay patient supine, connect to IV and topo the abdomen
Portal Venous abdomen performed
Images assessed and then a decubitus (left/right) [IV disconnected]non contrast abdomen performed based on clinical findings or indications, with balloon down
Tube removed and patient can clean up, hot drink, biscuit before cannula removed, patient informed of how to get results.
Patient preparation – is key to a good CTC
Recent eGFR or creatine to assess kidney function.
Cessation of iron tablets up to a week before.
Low fibre diet up to 24/48 hours prior to procedure.
Use of laxative (such as picolax) day before procedure.
Use faecal tagging 24 hours before study- provides double contrast.
NBM after midnight
Muscle relaxant
what foods are allowed and what to avoid
fruit/ fruit juices
- foods allowed
clear fruit juices
- please avoid
raw fruits
raisins
dried fruit
prunes and prune juice
drinks
- foods allowed
coffee
tea fizzy drinks
water
fruit flavoured drinks
alcohol unless advised not to
- please avoid
all others
soups
- foods allowed
clear or strained soups
- please avoid
all others
desert
- foods allowed
jelly fruit sorbet
- please avoid
coconut
nuts
seeds
miscellaneous
- foods allowed
salt
pepper
jelly
sugar
honey
- please avoid
cloves
seed spices
chili sauces
bbq sauce
strong spice
peanut butter
jam
questions to ask prior to
- are you allergic to iodine or had any complication with injected contrast or have severe multiple allergies? if yes, describe complication;
- if yes did you receive medication specific to iodine allergy 24 hours prior to the exam?
- are you dialysis? if yes when is your next dialysis appointment ?
- do you have a central venous line/ picc line/ port
- have you ever been diagnosed with asthma or use an inhaler? if yes please bring you inhaler to the ct scan appointemnt.
have u ever been diagnosed with diabetes
if so please list medication
are u taking metformin containing medications if yes please list medication
have you had kidney surgery or any kidney disea or any family history of kidney failure
have you had or are being evaluated for solid organ transplant failure
have u ever been diagnosed with myeloma lupus scleroderma gout sickle cell disease hyperthyroidism or myasthenia gravis.
Buscopan – all you need to know and more
Anticholinergic drug working on smooth muscles
Relaxes the bladder (urinary retention)
Relaxes the bowel improving colonic distension
Increases heart rate (1 hour)
Dilates the pupil (burred vision 45mins)
Effects normally lasts 15-20mins
Rarely causes acute glaucoma
Safe for patients with a stable heart rate
Glucagon is expensive and not very effective
Why do we distend the colon- what are we looking for ?
Topogram will show amount of air in the colon
Easy to miss pathology in collapsed segments
Collapse can simulate pathology when distention is inadequate
Normal colonic wall is 2-3 mm in diameter
For best distention
Use automated insufflation
Use CO2
Use antispasmodic
Always scan in 2 positions (supine & prone or decubitus)
Always review for collapsed areas and consider further insufflation or additional positions
Poor insufflation
Good insufflation
Positioning prone usually distension of ascending and colon rectum
Positioning supine usually results in distension of sigmoid and transverse colon.
Undertaking the procedure - Tube insertion
Left lateral position in a well-lit room
Privacy – The patient, you and a colleague
Lubrication
Be gentle, patients are normally sore from the bowel prep
Beware of anal pathologies
Catheter retention can be with tape or small retention balloon
Deflate for 2nd scan to avoid missing low rectal pathology
Undertaking the procedure - Tube insertion
Once you have enough air in the colon:
Supine abdomen and pelvis scan in the portal venous phase(70 second delay at 3mls a second)
Second view (non contrast abdo/pelvis, balloon down)
[If pathology seen on the look through of first scan add CT chest non-con for staging]
Complications – What is avoidable and unavoidable
Bowel purgation can cause:
Electrolyte imbalance
Cardiac dysthymias
Dehydration
Faint
Loss of efficacy
Oral contraceptive
The scan
Incorrect ID
Incorrect rectal cannulation
Contrast extravasation
Allergy
Bowel perforation
Diabetic hypoglycemia
Radiation incidences
Symptoms and sites of pathology
Right side
Widest section larger tumors and blood mixes with stool
Mass and anaemia
Left side
Narrowest section small tumors
Obstructive symptoms
Pathologies
Colorectal Cancer
Diverticulitis
Ileus
Polyp
Ulcerative Colitis
Crohn’s Disease
Diagnosing Colorectal Cancer on CTC
Shape of colon cancer is the same on any type of radiology:
Annular
Polypoidal
Obstructing
Second abnormalities are very difficult to see on barium enemas proximal to a stricture, but CTC is good at this
What to look for:
Homogeneous enhancement in tumors
Shouldering
Large polyps
Pathology of polyps and cancer
Polyps are tumors at the surface of an organ
Many types BUT adenomas are the ones that as a minority turn into cancer
Originate in the mucosa from crypts
Normally grow up and out into the lumen
Some develop a stalk to become pedunculated
Some are flat (sessile)
All start in small adenomatous polyps, grow large and change shape
if malignant they invade the muscularsis layer - allows spread
adenomas are more common in old age
if one is found high chance of finding a second one
Pathology of polyps and cancer
bengin
hyper proliferation
adenomatous polyps
dysplasia - pre cancer
malignant
adenocarcinoma
invasive cancer
Pathology of polyps and cancer
Colorectal adenomas are the precursor polyps to colorectal cancer
BUT their transformation to colorectal caner may take years!
AND the vast majority of adenomas never undergo this transformation!
CT COLONOGRAPHY VS ALTERNATIVES
CT COLONOGRAPHY
Minimally invasive (small flexible tube)
No ‘blind spots’ as virtual camera can be moved into any direction.
No sedation/anaesthetics required
Fast procedure
Radiographer and Radiologist
Low risk of perforation
COLONOSCOPY
More invasive (use of endoscope)
Natural blind spots due to limitations of the endoscope (corrected by movement)
Sedation required
Can take a long time
Gastroenterologist + nursing +anaesthetists +…
Higher risk of perforation
CT COLONOGRAPHY VS ALTERNATIVES
CT COLONOGRAPHY
3D imaging at point of undertaking.
No sedation required
Fast procedure
No blind spots due to virtual camera
BARIUM ENEMA
2D imaging across multiple planes
No sedation required
Can be lengthy depending on preferences
Blind spots due to ‘pooling’ of barium.
Advantages and disadvantages
Advantages
Quick
Less invasive
Good image quality
Short recovery time
Can review whole abdomen
3D imaging
Less labour intensive
No blind spots
Disadvantages
High radiation dose
Risk of contrast reaction
Risk of perforation
Risk of infection
Patient preparation dependant
