CT Colongraphy Flashcards
what is CT Colonography - 5 points
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
what types of CT Colonography are there - 7 points
unenhanced enhanced low dose faecally tagged untagged fasted non-fasted
clinical indications for CT Colonography - 5 points
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
contraindications for CT Colonography
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)
preparation for CT Colonography - 8 points
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?
positive contrast agents - 4 points
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
negative contrast agents - 4 points
absorbs x-rays less strongly (lower Z) than surrounding tissue/organ examined
radiolucent
CO2 - minimises discomfort as absorbed more quickly than air
Air
patient preparation for CT Colonography - 6 points
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
buscopan - 3 points
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
contraindications for buscopan - 5 points
myasthenia gravis narrow angle glaucoma tachycardia megacolon prostatic enlargement withe urinary retention
contrast questions - 9 points
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
procedure for CT Colonography - 6 points
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
who is CTC unsuitable for
unco-operative - e.g. severe dementia
unable to tolerate bowel cleansing
immobile - or cannot tolerate turning on their side
Ischaemic Heart Disease (IHD) sufferers
advantages of CTC - 8 points
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
disadvantages of CTC - 5 points
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
