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| Journal of the New Zealand Medical Association,
08-June-2012, Vol 125 No 1356
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Computed tomographic colonography: colonic and
extracolonic findings in an Auckland population
Helen Moore, Nicholas Dodd
Computed tomographic (CT) colonography is used to identify
individuals with polyps or cancers, in order to triage the appropriate patients
to colonoscopy and/or surgery. CT colonography is an established screening
technique for colorectal cancer, and in many centres has effectively replaced
barium enema as a first-line investigation in the patient with symptoms
suggestive of bowel cancer.
It may also detect other causes for the patient’s
symptoms, either related to the bowel (such as appendicitis or diverticulitis),
or non-bowel-related “extracolonic” problems such as lymphoma. Up to
10% of extracolonic findings (ECF) are potentially the cause of the symptoms
that lead to the CTC investigation.1
There is a large quantity of data available internationally
regarding the distribution of colonic and extracolonic findings, but limited
data as yet from New Zealand. This information is important in relation to
quality assurance and workflow planning in our local environment.
MethodsAll patients who underwent CTC in the 72-month period
from 1 January 2004 to 1 January 2010 were included in the analysis. CTC was
performed on either a 16 slice or 64 slice CT (GE Lightspeed series), after
standard bowel preparation with LoSo Prep (E-Z-EM).
A supine and prone (and/or occasionally a supplementary
decubitus scan) was performed for each patient. Standard technique factors were
40–50 mAs, 120 kVp or 100 kVp (latter if less than 75 kg weight), and
either manual air insufflation prior to 2009, or subsequently CO2 insufflation
(ProtoCO2l, Bracco Diagnostics).
Demographic data and CTC findings were recorded,
according to the CT Colonography Reporting and Data System
(CRADS).2 The CRADS code was prospectively
reported from mid 2008, and coding was retrospectively applied to the other
reports from 2004–2008 for the purpose of this study; after assessment of
the report by two experienced CTC radiologists. A group of six CTC accredited
radiologists reported the studies.
Results2152 consecutive CTC patients were available for study. The
group was 52.6% female, with an average age of 59.4 years; range 19–87
years. Indication data was unable to retrieved in 605 of the earliest patients;
(28%). Of the remainder, approximately 84% were symptomatic. The most common
indication was “change of bowel habit”, usually not otherwise
specified. 16% were asymptomatic (which included some higher risk patients also;
comprising 6 failed colonoscopy patients, 5 FOBT positive patients and 17
surveillance patients following colorectal cancer resection). Diverticular
disease was mentioned in 880/2152 reports; a prevalence of 41%. Of these
approximately 360 (also 41%) were reported as mild-trivial.
Table 1. Colonic findings, CRADS: CT
colonography reporting and data system
Colonic findings: The C2–C4 group comprises a total
potential referral rate to surveillance, colonoscopy or surgery, of 10.7%. For
extracolonic findings, the majority were normal or findings of no major
importance. The E3 and E4 group together comprise the total of potentially
significant extracolonic findings; of 8.3%.
Figure 1. Virtual dissection mode—view of
a cancer indrawing the wall of the ascending colon
 Figure 2. Volume-rendered “barium
enema” type view—the image demonstrates multiple sigmoid colon
diverticula, as well as a rectal polyp
 Table 2. Extracolonic findings
Figure 3. Coronal view of abdomen—common
extracolonic findings of a tortuous but not aneurysmal aorta with calcified
atheroma, and a hiatus hernia
 Table 3. Description of potentially significant
extracolonic findings
PUJ=pel-veoureteral junction.
DiscussionThere has been much debate in the literature as to whether
detecting extracolonic abnormalities is an “asset or
liability”;3 and there are valid issues
on both sides. The anxiety and possible physical complications provoked by
undergoing work-up of an incidental finding is not to be underestimated, and it
is difficult to measure this effectively; particularly in economic terms. The
potential financial and patient harm implications of extra testing generated
from CTC are a concern.
The impact of these issues can be tempered by having good
quality information regarding the prevalence and type of ECFs, and by having
guidelines/agreements in place as to how to categorise them and how to deal with
them. There is heterogeneity in how different studies have reported ECFs, and
particularly in relation to the definition of “significant”, or
“major” or “important” findings. These fall into two
main groups; findings of direct clinical importance e.g. a probable cancer, or
any finding that generates an extra investigation.
The Working Group for Virtual Colonoscopy has provided a
sound base for addressing this with the publication of the CT Colonography
Reporting and Data System (CRADS) in 2005,2
which although developed for a screening population, have been applied to and
adapted for use in symptomatic patients also.
4,5 The more recent “CT Colonography
Standards, an International Collaboration,”
6 published in 2010, has also contributed
significantly to this process.
Our study is aligned along the CRADs definitions, although
there may well be debate regarding specific categoratisation within each group.
In the future, clearer guidelines may be available but this is a tricky area;
because local practices may differ, availability of certain tests may differ,
and patient “culture” in regard to acceptance of surveillance or
active investigation may differ. Development of local guidelines may be a useful
endeavour.
Data from multiple centres around the World has shown that
extracolonic findings are present in at least half of the patients, and that
there is an increased frequency in older
patients,7 and in studies using intravenous
contrast and higher radiation dose techniques.8
Symptomatic patients and females have also reported to have more
ECFs.9 Despite the heterogeneity of study
designs, the rates of “significant” extracolonic findings that
require further work up or alter management are generally in the range of 6-16%,
although it has been reported at up to 25%, in a study using intravenous
contrast. 10
A recent Australian study of 258 symptomatic patients found
significant ECFs in 8.9% . 11 An asymptomatic
Australian cohort reported a rate of significant ECF in 7.4% .
12 These are both similar to our rate of
8.3%.
The majority of our E3 Group (probably benign but needs
further work-up) were renal or hepatic or ovarian cysts that could not be
clearly categorized as benign on the low dose CT, requiring only ultrasound
follow up. However, a limitation of this study is that the cost estimates of
these subsequent investigations has not been performed.
A recent USA study in a screening population of 2277
patients found a significant ECF rate of 11%, which generated extra cost of
approximately $50 per patient. They detected 6 cases of colorectal cancer, and 6
cases of extracolonic malignancy. 13
Our extracolonic potential malignancy detection rate of 1.8%
(39/2152) is close to our colonic potential malignancy detection (C4) rate of
2.36%; particularly as we know that some of these are false positive due to
pathology such as diverticular strictures, or the occasional polypoid mass that
is benign. Further follow up work will be required to ascertain the true rate of
extracolonic malignancy and the false positive C4 colon cancer rate in our
cohort.
A study from the Netherlands looked a group of 398
symptomatic patients, and applied the CRADs
classification.5 They reported a rate of 7.5%
of patients with C3-4 classification; i.e. with suspected colorectal cancer,
polyps >10 mm or >2 polyps 6-9 mm. 8.3% were C2 (1-2 polyps 6–9 mm);
for a total potential referral rate to OC of 15.8%. This may be due to the
increased prevalence of disease in their entirely symptomatic cohort. They had a
significant ECF rate of 15.6%.
An American study in a screening population reported 62/454
patients or 13.6% with at least one polyp >5
mm.7
In comparison to these studies, our polyp frequency is
lower. This is of uncertain significance; potentially due to different
population characteristics, or our detection rate may be lower. Comparison with
other national data is awaited, and reassuringly our miss rate for colorectal
cancer is well within the reported range, at
5.1%.14
This study is limited by its retrospective, descriptive
nature; but it provides useful local data.
ConclusionOur CTC population is largely symptomatic, and there is an
acceptable referral rate from CTC to colonoscopy, surgery or surveillance of
10.7%. The 8.3% rate of potentially significant extracolonic findings is at the
lower end of the reported international ranges, although in line with Australian
data. Ongoing work will be required to assess the performance of CTC in our
population.
Competing interests: None
declared.
Author information: Helen Moore, Consultant
Radiologist; Nicholas Dodd, Consultant Radiologist; Auckland Radiology Group,
Auckland City Hospital, Auckland
Acknowledgements: We thank National
Screening Unit, Ministry of Heath, for their funding contribution; NZ Branch
office, Royal Australian and New Zealand College of Radiologists for their
assistance; and Rachel Dodd for data collection.
Correspondence: Dr Helen Moore, PO Box
9889, Newmarket, Auckland, New Zealand. Email: Helen.moore@adhb.govt.nz
References:
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