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J. H. Bortz
Key Messages
• All cases of incomplete or failed OC must be
completed by CTC or CCE.
• CCE is more expensive than CTC.
• CCE has a difcult and prolonged bowel
cleansing procedure.
• CCE cannot visualise extracolonic pathology.
• Reasons for failed or incomplete OC include
diverticular disease, long bowel loops, acute
exure angle.
• Essential to exclude OC caused perforation
referred for CTC following an incomplete or
failed OC.
20.6 Summary
CTC is recommended in the literature as the
imaging alternative in patients with incomplete
and failed OC. Collaboration between radiologists and gastroenterologists is therefore important for optimal management and imaging of
incomplete colonoscopy patients.
References
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18. Pickhardt PJ.Screening CT colonography: how I do
it. AJR. 2007;184(2):290–8.
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screening? Eur Radiol. 2012;22(7):1495–503. https://
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Gastrointest Endosc. 2011;74:581–9.
Good Practice Reporting inCTC
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JoelH.Bortz
21
21.1 Introduction
A reader should check both intracolonic and
extracolonic structures when reporting on a CT
colonography (CTC) study. A successful CTC
examination means that the colon was well prepared and adequately distended for full visualisation of the six segments of the colon. Two views
are usually required, but additional views may be
necessary. The report must cover all aspects of
the study. The use of a template ensures all
required information is reported. CTC interpretation uses a combination of a 3D-2D approach in
which 3D is the most important. A screening
CTC examination does not require administration of intravenous (IV) contrast. It is indicated
when there is a known colonic or extracolonic
malignancy; non-ionic agents should be used. As
discussed in Chap. 8 some centres may administer an antispasmolytic, hyoscine-N-butylbromide
(Buscopan), for example, provided there are no
contraindications for its use. Glucagon is not
used because it is expensive, not effective, and it
has side-effects.
If a study is non-diagnostic due to poor quality, it is essential to report on extracolonic ndings (ECFs). Figure 21.1(i–iii) shows examples
of a non-diagnostic study due to excessive stool
in the colon. There were multiple areas of large
amounts of residual stool because the patient did
not follow the bowel preparation steps correctly.
The CTC was rescheduled. However, it is essential to report on any ECFs even if a patient is
rescheduled for a repeat CTC. The following
abbreviations are used in this chapter.
• AI: articial intelligence
• CAD: computer-aided diagnosis
• IVC: ileocaecal valve
• ECFs: extracolonic ndings
• FOV: eld of view
• HU: Hounseld unit
J. H. Bortz (*)
LSG Imaging, Los Angeles, CA, USA
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023
J. H. Bortz et al. (eds.), CT Colonography for Radiographers,
https://doi.org/10.1007/978-3-031-30866-6_21
301
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(i) (ii)
(iii)
J. H. Bortz
Fig. 21.1 (i) 3D view showing stool (arrows). (ii) 2D view showing stool (arrows). (iii) TD view showing stool (arrows)
21.2 Reading andInterpretation
Requirements
Accurate reading and interpretation of CTC studies should be done by a radiologist, or an appropriately trained radiographer. Readers of CTC
studies should be familiar with normal colon
anatomy and variants, such as the different
appearances of the ileocaecal valve (ICV).
Figure 21.2a–e depicts variations of ICVs (see
Chap. 11 for more examples).
It is important to be able to distinguish resid-
ual stool from polyps. Potential pitfalls should be
recognised (see Chap. 12). Reading and interpretation requires knowledge of the various pathologies that occur within the colon wall, as well as
ECFs (see Chaps. 18, 19, and 20). How to measure polyps is discussed in Chap. 14, as are the
different sizes of polyps, and polyp subsets.
In 2005, the C-Rads-CT colonography reporting and data system was introduced for reporting
both asymptomatic screening studies and diagnostic studies. Suggested feature descriptors for
polyps and masses are presented in Table 21.1
[1]. In terms of Table 21.1, the following is
important.
ab
cd
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303
e(i) e(ii)
Fig. 21.2 (a) Bulbous ICV (arrows). (b) Bulbous (polyp-
oidal) ICV (arrows). (c) Vulval type ICV (arrows). (d)
Partially patent ICV (arrow). (e) (i) 3D endoluminal
supine view showing ICV (arrows). (ii) 3D endoluminal
prone view of the same patient shows change of shape of
the ICV (arrows)
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J. H. Bortz
Table 21.1 Suggested feature descriptors for polyps and
a
masses
Size (mm) Always measure the largest diameter
in the correct plane, i.e. axial, sagittal
or coronal plane
Morphology
(form/shape)
Location Polyps may be present in any part of
Attenuation Refers to the density of the lesion
a
Adapted from [1]. Zalis etal. CT colonography reporting
and data system: a consensus proposal. Radiology 2005;
236 (1):3–9. [https://doi.org/10.1148/radiol.2361041926]
Refers to the type of polyp present,
namely, sessile, pedunculated, at or
carpet lesion
the colon and may be single or
multiple. The colon is divided into six
segments for CTC as discussed in
Chap. 11: rectum, sigmoid colon,
descending colon, transverse colon,
ascending colon, and caecum
being investigated
• Measurement of polyps
• An extremely accurate measurement of a
polyp is required. For example, a variation of
1–2mm may convert a normal CTC study into
an optical colonoscopy (OC) rather than a
3-year surveillance programme if, for example, a 9mm polyp is measured incorrectly.
• Size of polyps
– Polyps may be divided into: diminutive
polyps ≤5 mm; small polyps ≥6–9 mm;
large polyps ≥10 mm (advanced
adenoma).
– A study is considered to be positive when a
polyp size is ≥6mm.
– All polyps ≥10mm are removed via opti-
cal colonoscopy.
• Morphology: the type of polyp found
– Sessile: A broad base of attachment to the
colonic mucosa.
– Pedunculated: It consists of a head and
stalk; only the head of the polyp is measured and not the length of the stalk.
– Flat polyp: A at lesion usually raised
about 3mm above the colonic mucosa; it is
often identied on CTC by having a barium
coating on the surface as a result of
tagging.
– Carpet lesion: A laterally spreading super-
cial tumour occurring mainly in the caecum and rectum.
• Location
– A polyp may occur in any segment of the
colon and may be multiple.
• Attenuation: Polyps and tumours measured in
Hounseld units (HU) to indicate the density
of a lesion
– HUs vary between polyps, tumours, air,
water, and bone and show an increase in
value following iv contrast enhancement
[2, 3]. As an example, the HU value of air
is −1000, water is 0 HU, dense bone is
+2000HU, and metal is +3000HU.
– Polyp HU values will change from pre-
enhancement value to post-enhancement
value [3]; unenhanced polyp 30± 15 HU
and post-enhancement 90±18HU [3].
– Colorectal cancers: Pre-enhancement
43 ± 15 HU and post-enhancement
124±18HU [3].
– Solid faecal residue: 43±15HU [3].
The reporting and data system created a common language for CTC studies. It is similar to
BI-RADS (breast imaging reporting and data
system) that has been successfully used for mammography reporting. The C-Rads system provides consistency of reports between individuals
and institutions. An advantage of the system is
that it allows valid comparisons of CTC data in
clinical and research settings. Knowledge of denitions of polyps and colonic masses, for example, is necessary to use the C-Rads system.
Chapter 14 presents a detailed discussion of polyps including denitions.
21.3 Interpretation Tools
forCTC
A combination of a 3D-2D approach is used for
CTC interpretation; 3D is the most important.
Software is required to transition easily between
3D and 2D viewing for detection and measurement of polyps, other polypoidal pathology, and
internal haemorrhoids. CAD (computer-aided
diagnosis) may also be used [4, 5]. Articial
intelligence (AI) can also be used for polyp diagnosis [6] (see Chap. 25).
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305
The author has used V3D Viatronix (Stony
Brook, NewYork) since 2000. It is currently the
only CTC software in the USA with FDA
approval. Viatronix tools allow the following.
• Segmentation and creation of 3D model
• Bookmarking
• Tracking 3D mucosal coverage
• Translucency rendering (i.e., a semi-
transparent view in different colours beneath
the surface): stool and polyp
• Measurement
• Volume measurement
• Electronic cleansing
These tools allow a user to segment out the
colorectum to create the 3D model and ythrough. An automated centre-line allows a
reader to focus on polyp detection without having
to manually produce such a line. Even if there is
a break in the colonic outline, the centre-line is
present in the next section. The current software
now allows for a eld of view (FOV) of 120°
which gives more coverage; a single y-through
from rectum to caecum may cover up to 90% of
the colon lumen. A 90° FOV required four ythroughs. The 120° FOV only requires two ythroughs due to increased visualisation.
As described in Chap. 10 when the supine and
prone scanned images have been obtained they
are then checked. The scanned images are sent to
PACS as well as to the Viatronix workstation
(Fig.21.3a). It is at this stage that a 3D model for
the y-through has to be created. A full air column outlining the colon may be obtained in a
substantial number of scans. This requires accessing all the scanned supine and prone data. Some
cases may present with discontinuity in the colon.
Figure 21.3b(i–vi) shows breaks in the colon.
Breaks in colon distension may be the result of (i)
incomplete distension of a segment of colon or
(ii) a column of uid in a portion of the colon,
which does not allow the CO2 to pass through.
These breaks usually occur in the hepatic exure
region as well as the sigmoid colon as demonstrated in Chap. 10.
In a small percentage of patients, reux of
CO2 into the terminal ileum may occur, and in
some patients it may track all the way up to the
stomach (see Fig. 21.3c(i)). These areas are
excluded from the colon-map view in the automatic centre-line creation; this results in a 3D
map view of the colon only as shown in
Fig.21.3c(ii).
When a polyp is detected manual navigation is
possible by holding down the left button on the
mouse in order to navigate fully around the polyp.
The Viatronix software includes a bookmarking
tool. When a polyp is detected, its position may
be bookmarked on the colon-map with a red dot
as evident in Fig.21.3d. This allows for a quick
review of the scan. It is best to describe a polyp’s
location according to the six segments of the
colon (rectum; sigmoid colon; descending colon;
transverse colon; ascending colon; caecum).
Although the centre-line measurement from the
anorectal region to the caecum is accurate, it seldom corresponds to colonoscopic measurements.
This is because at optical colonoscopy the bowel
is pushed and pulled to advance the colonoscope
forward, whereas at CTC no interference with the
bowel occurs. Measurement of polyps is covered
in detail in Chap. 14. It is essential to address
ECFs in the report as underscored in Chap. 18.
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a
b(i) b(ii)
Fig. 21.3 (a) Viatronix V3D workstation showing
images of a patient and icons. A 3D image must always be
in the centre when we commence viewing. Right side
shows 2D views (axial at the top; sagittal in the middle;
and coronal at the bottom). Each 2D view can be viewed
separately clicking the icon. Top left image shows a
colon-map with automated green centreline. Below it is a
2D perpendicular view of the 3D image in the centre. The
icons at the centre of the screen below the 3D images are
used, for example, for direction of ow and speed. (Image
courtesy of Viatronix, Stony Brook, New York). (b) (i)
Supine with four breaks. R rectum; DC descending colon;
TC transverse colon; AC ascending colon; C caecum. (ii)
Prone view shows a break in proximal TC and gap in
bowel. This is fully covered in the supine in (i); therefore,
the study is complete.
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b(iii) b(iv)
b(v) b(vi)
307
Fig. 21.3
colon; DC descending colon; TC transverse colon; C caecum. (iv) Prone showing entire colon distended. R rectum; DC descending colon; TC transverse colon; AC
ascending colon; C caecum. (v) Gap proximal transverse
(iii) Supine two breaks. R rectum; SC sigmoid
colon in LLD view. C caecum; AC ascending colon; TC
transverse colon; DC descending colon; R rectum. (vi)
Gap proximal transverse colon covered in RLD view thus
study complete. C caecum; AC ascending colon; TC transverse colon; R rectum.
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c(i) c(ii)
d
Fig. 21.3
transverse colon; SB small bowel; C caecum; R rectum.
(ii) Complete colon-map after automatic removal of stomach and small bowel by Viatronix software. R rectum; SC
(c) (i) Reux of CO2 into the stomach (S). TC
sigmoid colon; DC descending colon; TC transverse
colon; AC ascending colon; C caecum. (d) Colon-map
showing two red dots indicating the site of lesions (open
white arrows)
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