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14 Polyps: Types andSizes
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185
1mm or more increase in a polyp’s size will indicate growth and may tip the patient into the
10 mm range where an OC then becomes
necessary.
Linear polyp size is dened by the longest
dimension among the three orthogonal 2D multiplanar reconstruction views: axial, sagittal, and
coronal. Electronic calipers are used for linear
measurements of polyps. Volume measurement is
a newer and more promising technique; a small
change in polyp diameter corresponds to a much
larger proportional change in polyp volume.
Figure 14.2i (i–iii) illustrates volume measurement. Volume measurement’s margin of error is
more relaxed than that of linear measurement
[23].
The Viatronix V3D System, which the author
uses, is able to provide automated measurements,
but there tends to be some ‘overow’ of the correct borders of a polyp as shown in Fig.14.2i (i–
ii). This software does however allow for a
semi-automated method of volume determination
using 2D images; currently, it is more accurate
than the automated method.
For accurate measurement of polyps in 2D,
the following window settings are used: W 2000
HU, L 0 HU.In the 3D setting, accurate measurement is dependent on positioning the polyp in a
head-on (en face) position, and not looking down
the colon lumen to measure. When in the correct
3D endoluminal position, the electronic callipers
are placed at the edge of the polyp. Care must be
taken to not include the penumbra or polyp
shadow.
The real importance of accurate measurement
occurs at a critical threshold. This is between a
diminutive polyp at 5mm and a small polyp at
6mm, as well as between a small polyp at 9mm
and an advanced adenoma at 10mm. The signicance of the latter is discussed in Chap. 15.
Should a polyp be covered by barium then an
oversizing would occur if only 3D measurements
were to be taken. This is because on 3D viewing
barium is not observed unless translucent display
(TD) is used; this allows visualisation of the
internal architecture of the polyp. By switching
to 2D measurement, ‘downsizing’ of the polyp
would occur with the barium coating being
excluded from the measurement.
When measuring in 2D, the orthogonal plane
that most closely aligns to the long axis of the
polyp is selected. In the 3D endoluminal view,
the line (red=2D axial view; green=2D sagittal
view; blue=2D coronal view) must pass through
the long axis of the polyp as shown in Fig.14.2j
(i–iii). In these gures, the red line corresponds
to the 2D axial view, and the line runs through the
short axis (middle) of the polyp. If we use this
measurement, the polyp will be incorrectly measured, and the polyp will be undersized. If we use
the green line on the 3D endoluminal view, it also
passes through the short axis of the polyp. It
would not be the correct one to choose as it also
under-measures true polyp size. If we look at the
3D endoluminal view with the blue line, corresponding to the 2D coronal view (Fig.14.2j (iv)),
it passes through the long axis of the polyp and
will be the most correct measurement.
Clinical audits of polyp measurements in CTC
studies should be performed regularly as part of
the quality improvement process that focuses on
patient care, management, treatment, and outcomes. The principles of clinical audit are discussed in Chap. 27.
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a(i) a(ii)
a(iii) b(i)
J. H. Bortz
b(ii) b(iii)
Fig. 14.2 (a) (i) 3D endoluminal view showing 4 mm
haustral fold polyp (arrow). (ii) 2D view showing density
on haustral fold (arrow=polyp). (iii) 3D view showing a
3.4 mm sessile polyp on posterior haustral fold (green
arrow). Anterior fold (open white arrow) and direction of
ight=open black arrow. (b) (i) 3D view showing small
(7.5mm) sessile polyp on posterior aspect of h. (ii) 2D
coronal view showing sessile polyp arising from posterior
fold (arrow). (iii) TD showing typical features of a polyp:
high intensity centrally (red) surrounded by light green
and blue.
14 Polyps: Types andSizes
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c(i) c(ii)
d(i) d(ii)
187
d(iii) e(i)
Fig. 14.2
on haustral fold. (ii) Sagittal 2D view showing polypoidal
density on end of fold (blue arrow). (d) (i) Rectal catheter
(C). Small sessile polyp on valve of Houston (white
arrows). (ii) 2D sagittal view showing small density on
inferior haustral fold (white arrow). (iii) Typical features
(c) (i) 3D view showing small polyp (6.5mm)
of a polyp on a TD view. High intensity centrally (red)
surrounded by light green and blue (open white arrow).
Rectal catheter (C). (e) (i) 3D view of a 9 mm sessile
polyp (open white arrows) on posterior haustral fold.
Polyps on posterior folds are frequently missed on optical
colonoscopy.
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J. H. Bortz
e(ii)
f(i)
e(iii)
f(ii)
f(iii) g(i)
Fig. 14.2
on posterior wall of caecum (open white arrow).
RK=right kidney. Right rib (green arrow). (iii) Typical
features of a polyp (open white arrow) on a TD view. High
intensity centrally (red). (f) (i) Large pedunculated polyp
on a thick stalk. (ii). 2D axial view showing pedunculated
polyp on stalk (white arrow) with barium surrounding the
(ii) 2D sagittal view showing soft- tissue polyp
polyp head (open white arrow). Note adjacent soft-tissue
sessile polyp (open green arrow). (iii) TD showing high
intensity (red) of polyp head. (g) (i) 3D endoluminal view
showing 12mm advanced adenoma. Note the broad-base
sessile polyp attachment (open black arrows) on haustral
fold with lobulated outline.
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g(ii)
h(i)
g(iii)
h(ii)
h(iii)
Fig. 14.2
polyp on anterior sigmoid fold. Note the small amount of
barium at the base and side. (iii). TD showing classical
features of a polyp (open black arrow). Note large central
area of high intensity (red) surrounded by light green and
blue colouration. (h) (i) 3D view showing a triangular
shaped 11.6mm sessile polyp (open black arrow mm) on
(ii) 2D sagittal view showing 12 mm sessile
i(i)
haustral fold. (ii) 2D axial view showing an elongated
density in relation to haustral fold (open green arrow). (iii)
TD showing features of a sessile polyp (open black
arrow). Note high intensity centrally (red) surrounded by
light green and blue. (i) (i) 3D endoluminal volume measurement of a sessile polyp. Note the slight overow of
purple at the base (open black arrow).
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i(ii) i(iii)
j(i) j(ii)
J. H. Bortz
Fig. 14.2
(purple). (iii). 2D view of the polyp that is coloured red for
volume measurement. (j) (i) 3D endoluminal with a red
line (corresponding to 2D axial view) passing through the
short axis of the polyp. Measurement in this view will
undersize the polyp. (ii) 3D endoluminal view with a
green line (corresponding to 2D sagittal view) passing
through the short axis of the polyp. Measurement in this
(ii). 3D endoluminal head-on view of the polyp
j(iv)j(iii)
view will undersize the polyp. (iii) 3D endoluminal view
with a blue line (corresponding to 2D coronal view) passing through the long axis of the polyp. This indicates the
correct measurement of the endoluminal view. The measurement on 2D coronal will be the correct measurement
of the polyp. (iv) 2D coronal view shows linear measurement through the long axis of the polyp
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14.5 Reporting Polyps: C
Classication
A C1 to C4 classication is used when reporting
CTC ndings (Table14.1). For example, normal
colon or a benign lesion would be classied as
C1. If a polyp or possibly advanced adenomas
were noted in the study, the classication would
be C3 [16].
• C0=non-diagnostic study.
• CI=routine screening every 5years because
no visible abnormalities of the colon and no
polyp ≥6mm.
• C2 = colonoscopy or surveillance recom-
mended if there are 2 or less 6–9mm polyps
present. If 3 or more polyps present, then only
option is OC and polypectomy.
• C3 = colonoscopy and polypectomy recom-
mended if more than 2 polyps 6–9mm present
(↑ risk of developing advanced adenoma).
Any polyp ≥10 mm represents an advanced
adenoma; OC and polypectomy
recommended.
• C4 = A malignant appearing colonic mass is
detected, which may compromise bowel
lumen or demonstrate extracolonic invasion,
such as lymphadenopathy or distant metastases. Surgical consultation recommended.
A revised C-Rad classication is work in
progress and should be published in the near
future.
Table 14.1 Colonic classications
C1 Normal colon or benign lesion
C2 Small polyps
C3 Polyp: advanced adenoma possibly
C4 A likely colonic mass
a
Adapted from Zalis etal. [16]
a
14.6 Natural History ofPolyps
According toLesion Size
In nearly all cases, the largest lesion will be
diminutive (≤5mm). By design, most large CTC
trials have not reported diminutive lesions.
Invasive cancer in this group is so rare that it can
be assumed to be non-existent in terms of population screening [24]. A CTC study without polyps
6mm or larger would be considered a negative
study and would be classied C1 (normal).
According to van Dam et al. [25], a future
trends report, published by the American
Gastroenterological Association in 2004, noted
that ‘polyps ≤5mm in size do not appear to be a
compelling reason for colonoscopy and polypectomy’. Ransohoff [26] concurred by stating ‘few
clinicians would likely argue that colonoscopy is
justied’ for these lesions and added ‘the overwhelming majority cannot possibly represent an
important near-term health threat’.
Bond [27] is of the opinion that scientic data
indicated that clinicians should shift their
attention away from simply nding and harvesting all diminutive colorectal polyps. Their attention should rather focus on strategies that allow
for reliable detection of the much less common,
but more dangerous advanced adenoma. One
third of diminutive polyps are adenomas; mainly
tubular adenomas. The remainder are nonadenomas; hyperplastic polyps and mucosal tags, for
example.
Lesion size is the most important factor of
clinical signicance. A CTC study is considered
negative if no polyps are identied, or if there are
polyps present that are all diminutive (≤5mm) in
size. The majority of diminutive lesions are
hyperplastic or tubular adenomas and are of little
or no clinical signicance [27]. According to
Schoenfeld [28], it is not necessary to report
diminutive polyps. The chance of these lesions
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being malignant or containing high-grade dysplasia at the time of detection is estimated to be far
less than 1% [29]. Others maintain that it is neither clinically wise nor cost-effective for diminutive polyps to be referred for polypectomy [12].
It is only the extremely rare diminutive
advanced adenoma that will likely grow over a
period of 5years and will then require removal.
Invasive cancer in the diminutive size range is
very rare hence can be assumed to be non- existent
in terms of screening population. OC detection of
diminutive lesions, and matching with CTC ndings can be problematic: additional time and
costs are incurred, as well as potential complications [24].
The prevalence range for polyps >6mm in an
asymptomatic screening population is 14% [1].
This means that 8% of individuals will have a
polyp in the 6–9mm range, and 6% will have a
polyp ≥10mm. For polyps larger than 6mm, the
ratio of adenomatous polyps to nonadenomatous
polyps reverses; two-thirds of polyps >6mm will
have adenomatous tissue.
The screening prevalence of small polyps is
about 8%, and the frequency of advanced adenoma in them is 4% [26]. The presence of highgrade dysplasia in small polyps is 0.05%, i.e. 5in
10,000 cases. The chance of a small polyp harbouring an invasive cancer is 0.2%, i.e. 2in 1000
cases [27, 29]. Small polyps are usually benign;
two-thirds are adenomatous polyps, and the
remainder are nonadenomas.
CTC studies, from the National Naval Medical
Center in America, and the University of
Wisconsin screening programme, have shown
that for small polyps the sensitivity is in excess of
90%, and the positive predictive value (PPV) for
them is more than 90% [30]. Hofstad etal. [31]
are of the opinion that leaving small polyps for
3years was a safe practice. Pickhardt and Kim
[1] concur; many studies have shown that leaving
small polyps in place is not a harmful practice.
A same-day OC or a 3-year surveillance
period is the clinical management of visualisation of one or two small polyps at CTC (see
Table14.1 as well as Table 10.2 in Chap. 10). The
working group on CTC (virtual colonoscopy)
underscore that 3-year CTC surveillance for
J. H. Bortz
Fig. 14.3 Colon-map showing three lesions. The three
red dots indicate site of pathology
patients with one or two small polyps represents
a reasonable approach [16]. If three or more polyps are seen at CTC, then OC is recommended;
there is a greater likelihood that such polyps contain adenomatous tissue. Figure14.3 shows three
lesions in the right side of the colon.
14.7 Small Lesions (6–9mm)
According to Pickhardt etal. [32], polyps that are
between 6 and 9 mm are usually benign, and
approximately 30% of such polyps are not adenomas. Of the small polyp group (6–9mm), 96%
lack high-grade dysplasia [33]; the probability of
a 6–9 mm polyp not representing an advanced
adenoma is approximately 96%. In other words,
the likelihood of a lesion this size harbouring an
invasive carcinoma is <1% [27]. It is reasonable
to recommend interval surveillance in 3 years
when one or two 6–9mm polyps are detected in
patients who do not have increased risk factors,
such as no rst-degree relative with a history of
CRC, or no personal history of CRC or advanced
adenoma. If a patient has three or more synchronous adenomatous polyps, then there is an
14 Polyps: Types andSizes
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193
increased risk of developing advanced adenomas
[34]. When three or more synchronous 6–9mm
polyps are detected at CTC, referral to OC and
polypectomy is recommended. Note that lesions
10 mm or larger, and colonic masses ≥30mm,
are referred for OC.
14.8 Advanced Adenoma
An advanced adenoma (>10mm, large polyp) is
at higher risk for cancer progression. It represents
the key target sign for CRC screening and prevention (Fig.14.4) [35]. Between 90 and 95% of
advanced adenomas are 10mm or larger in size
[10]. Only adenomas and serrated polyps have
the possibility of future transformation into cancers [36]. Despite the overall preponderance of
subcentimetre lesions, only a small minority of
advanced adenomas are present; the vast majority
Fig. 14.4 The target is
an advanced adenoma
of them have a villous component rather than
high-grade dysplasia [10]. It is believed that if an
advanced adenoma has a tubulovillous or villous
component then there is a slow progression to
cancer conversion [37].
There are three criteria of an advanced ade-
noma [10].
• Any adenoma that is large (≥10mm) and of
any histological subtype, namely tubular,
tubulovillous, or villous.
• Any adenoma of any size that harbours highgrade dysplasia.
• Any adenoma of any size that contains a signicant villous component (≥25% of tubulovillous or villous histology).
Advanced adenomas are located throughout
the colon; proximal and distal distribution is
almost equal. The cancer rate for large adenomas
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J. H. Bortz
Table 14.2 Comparison of CTC vs OC for detection of
advanced adenoma
Primary CTC cases (n=3120)
• Patients referred for OC
(n=246/8%)
• Polyps removed at OC
(n=561)
Invasive cancer (n=14) Invasive cancer
Perforations (n=0) Perforations
a
Adapted from Kim etal. [10]
a
Primary OC cases
(n=3163)
• NA
• Polyps removed
(n=2434)
(n=4)
(n=7/0.2%)
(10–20 mm) is only about 1%. Approximately
30–40% of large polyps are nonadenomatous
[32]. A comparison of CTC versus OC for detection of advanced adenoma is presented in
Table14.2.
The number of advanced adenomas ≥10mm
was identical in both groups; the total number of
advanced neoplasia (i.e., all advanced adenomas
and carcinoids was almost identical [10]. As
shown in Table 14.2, only 8% of patients who
had CTC examinations were referred to OC and
out of these patients 561 polyps were removed
compared with 2434 removed at OC.This indicates a four-fold increase in the number of polyps
removed during OC. This is indicative of the
unnecessary removal of a large number of benign
lesions.
Of signicance there were seven perforations
at OC and nil in the CTC group. The major nding in the study being that in an almost identical
number of patients, 14 cancers were detected in
the CTC group (n=3120) compared with 4 cancers detected in the OC group (n=3163).
14.9 Adenomatous Polyps
These are benign neoplastic lesions. However,
over time change may occur with the gland component of a polyp: a condition known as dysplasia (abnormal growth/development of tissue, for
example). The latter is graded from mild through
to severe then to advanced. When this occurs, the
polyp is then called an advanced adenoma. When
the cancer penetrates the muscular layer of the
bowel wall, it is termed an ‘invasive’ cancer.
Based on their glandular architecture, there are
three subsets of adenomatous polyps. These subsets and their prevalence percentages are listed
below.
• Tubular adenoma (80–85%)
• Tubulovillous adenoma (10–15%)
• Villous adenoma (<5%)
Adenomatous polyps usually contain both
glandular and villous components. The percentage of villous components in the histology indicates which subset classication is applicable
and also its malignancy potential.
• Tubular adenomas usually contain less than
25% villous architecture.
• Tubulovillous adenomas contain between 25
and 75% villous component.
• Villous adenomas usually have >75% villous
component.
The risk of malignant change increases with a
high villous component. Although villous adenoma are uncommon, their incidence increases
with advancing age. The most common sites for
these polyps are the caecum and rectum.
Adenomatous polyps have the potential to grow
into cancer: approximately 3% will develop into
cancer. On average, as a result of genetic
mutations, it may take between 10 and 15years
for a benign polyp to convert to a malignant one.
Such an occurrence is called the adenoma-carcinoma sequence or pathway (see Chap. 15). This
sequence occurs in 85% of sporadic rectal cancers: small→large ones >10mm→non- invasive
carcinoma→invasive carcinoma [36].
An adenoma with high-grade dysplasia has the
greatest risk of progressing to cancer [37]. Highgrade dysplasia is now the preferred terminology
and not carcinoma in situ. An invasive carcinoma
refers to cancer that spreads beyond the muscularis mucosa into the submucosa. When this occurs,
the cancer can potentially spread further. A malignant polyp is an adenoma with invasive carcinoma: the polyp has invaded past the muscularis
mucosa into the submucosa, and metastasis may
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