CT Colongraphy Flashcards

1
Q

what is CT Colonography - 5 points

A

removal of faeces via bowel cleansing with either diet change or fasting in order to distend the large bowel

distention - use of CO2 via rectal intubation

same radiation dose as a barium enema

scans in prone, supine and lateral positions

all patients must have motility and understand the importance of the bowel cleansing regime

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2
Q

what types of CT Colonography are there - 7 points

A
unenhanced
enhanced
low dose
faecally tagged 
untagged
fasted
non-fasted
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3
Q

clinical indications for CT Colonography - 5 points

A

patient with strong suspicion of cancer
too frail or major aversion to endoscopy
incomplete colonoscopy
palpable abdominal mass related to colon
tumour on flexi-sig - to stage and assess rest of colon for synchronous lesions

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4
Q

contraindications for CT Colonography

A

colitis/diverticulitis - patients will have acute diarrhoea and abdo pain
recent biopsy/surgery of bowel - wait 2 weeks/consult with consultant
immobility or recent MI (wait 6 weeks)

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5
Q

preparation for CT Colonography - 8 points

A
eGFR
x-ray contrast reaction history
iodine reaction history
?previous bowel surgery
?recent biopsies
diabetes (on metformin)?
recent barium upper GIT exam - contrast residue?
faecal loading/constipation history - extended cleansing bowel regime?
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6
Q

positive contrast agents - 4 points

A

absorbs x-rays more strongly (higher Z) than surrounding tissue/organ examined
radiopaque
gastrografin - oral - iodine based - used for faecal tagging
optiray 300 - IV - iodine based

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7
Q

negative contrast agents - 4 points

A

absorbs x-rays less strongly (lower Z) than surrounding tissue/organ examined
radiolucent
CO2 - minimises discomfort as absorbed more quickly than air
Air

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8
Q

patient preparation for CT Colonography - 6 points

A

low residue diet 3 days prior - no fasting/formal laxative
2 days prior = 1 x GG with evening meal
1 day prior = 1 x GG with lunch and 1 x GG with evening meal
Patients <70 or severe constipation = 3 x30ml GG mixed with pint of water
patients >70 or frail/limited motility/renal failure = 3 x 20ml of GG mixed with pint of water
GG = laxative effect due to its high osmolarity

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9
Q

buscopan - 3 points

A

anti-spasmodic
relaxes smooth muscle of bowel wall by preventing acetylcholine acting on the muscle - blocks the receptors
allows muscle to relax to prevent spasms/cramps

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10
Q

contraindications for buscopan - 5 points

A
myasthenia gravis 
narrow angle glaucoma 
tachycardia 
megacolon
prostatic enlargement withe urinary retention
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11
Q

contrast questions - 9 points

A
allergies - buscopan/contrast
asthma - 6x likely to react to contrast
diabetes 
renal failure 
multiple myeloma
renal function - normal = >90 
<60 = monitoring post 48hrs
<30 = can't give contrast with renal team consent and pre/post iv contrast hydration but can with patients having dialysis because bloods normal after
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12
Q

procedure for CT Colonography - 6 points

A

rectal exam - can be difficult to assess on CT
insert tube and inflate balloon if safe
20mg Buscopan via IV
2 litres of CO2
assess pneumocolon with scout - patient retaining CO2?
perform prone scan

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13
Q

who is CTC unsuitable for

A

unco-operative - e.g. severe dementia
unable to tolerate bowel cleansing
immobile - or cannot tolerate turning on their side
Ischaemic Heart Disease (IHD) sufferers

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14
Q

advantages of CTC - 8 points

A
little/no risk of perf
quick (roughly 15 mins)
no sedation
less painful and better tolerated than conventional colonoscopy 
extra-luminal can be easily identified
same day chest-staging 
cheaper
tailored technique if elderly or infirm
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15
Q

disadvantages of CTC - 5 points

A

radiation dose
power bowel cleansing = reduction in accuracy of report
can’t biopsy so non-therapeutic
risk of x-ray contrast reaction
may detect incidental irrelevant pathology that may instigate further unnecessary management
flat lesions may be missed

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16
Q

what happens after a failed colonoscopy

A

CTC can be performed same day avoiding repeats
however will be untagged and reduction in sensitivity of visualising small lesions/polyps
if endoscopy failed due to faeces, a same day non-tagged CTC will be non-diagnostic