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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_770_Библиотеки_им_академика_М_И_Перельмана
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c(i)
c(iii)
c(ii)
d(i)
d(ii) e
Fig. 12.3
(c) (i) 3D view showing thickened haustral fold
(arrow). (ii) Axial 2D showing barium surrounding haustral fold (white arrow). (iii) TD conrming barium (black
arrow) and not a polyp. (d) (i) 3D endoluminal view
showing a sessile lobulated polypoidal lesion (arrow). (ii)
TD showing stool (arrow) and not polyp. (e) Adherent
non- opacied stool having indentations similar to the
appearance of the surface of a golf ball (arrows)
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a(i) a(ii)
Fig. 12.4 (a) (i) 3D view showing stool (arrow) that may be obscuring lesions. (Courtesy of Viatronix, Stony Brook,
NY). (ii) 3D view showing artefacts (arrows) caused by electronic cleansing. (Courtesy of Viatronix, Stony Brook, NY)
J. H. Bortz
Same-day CTC examinations, after an incomplete or failed optical colonoscopy (OC), tend to
be sub-optimal as tagging has not been performed
(see Chaps. 10 and 20) [4]. Untagged stool is a
huge problem. Electronic cleansing is available
on most software systems, which allows for visualisation of mucosa covered by uid and/or stool.
On the other hand, electronic cleansing creates
subtraction artefacts that present interpretation
problems. This is counterproductive as the produced artefacts are unwanted and impact on
image evaluation. Electronic cleansing is not routinely performed because it may cause a large
number of artefacts which may make interpretation difcult. In addition, part of the surface
mucosa may be electronically removed and this
could result in missed lesions [4]. The author
does not use electronic cleansing because it
causes artefacts. Pickhardt and Kim (personal
communication) advise against using electronic
cleansing in CTC studies.
12.2.3 Sigmoid Diverticular Disease
group. How can this potential pitfall be overcome? The use of spasmolytics enables improved
bowel distension [4]. In Europe, and South
Africa, Buscopan is often used to relax the bowel
for good distension (see Chap. 8).
Another potential trap is that of stool-lled
diverticula. On 3D, it may produce an appearance
of a polyp. The complementary role of 2D identies stool-lled diverticula as discussed in Chap.
16. Figure12.5b is an example of 2D showing an
impacted diverticulum.
12.2.4 Morphology ofPolyps
The shape and form of at lesions and carpet
lesions are potential pitfalls. Polyp measurements
can be a potential interpretation trap. It is important to ensure measurements are accurate as discussed in Chap. 14. Shifting pedunculated polyps
can be potential interpretation traps. It is important to use a 2-view scan for 3D and 2D evaluation as evident in Fig.12.6 (i) and (ii).
This disease is covered in more detail in Chap.
16. For the purpose of discussion, the following
potential traps are presented. Poor or incomplete
luminal distension and thickened folds
(Fig. 12.5a), underpin potential pitfalls in this
12.2.5 Anatomical Locations
andStructures
Both the location and structure of the appendix,
and the ileocaecal valve (ICV) are potential inter-
ab
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Fig. 12.5 (a) Axial 2D showing very poor distension of
the colon (open black arrows) and multiple diverticula. (b)
2D axial view shows stool (white arrow) and impacted
diverticulum (green arrow). Yellow arrow shows diverticulum lled with air
(i) (ii)
Fig. 12.6 (i) 3D endoluminal view showing pedunculated polyp (black arrow) on a short stalk (open black arrow). (ii)
Axial 2D view shows pedunculated polyp (white arrow)
pretation traps when evaluating CTC images. The
vermiform appendix is part of the caecum. Its
length varies from 2.5 to 33cm [8]. Its average
12.2.6 External Impressions
ofOrgans andBony
Structures ontheColon
length is between 5 and 10cm and its base is usually situated 2 cm below the ICV. Its intraabdominal position may vary widely depending on
the peritoneal fold which represents the mesentery
of the appendix [8]. Figure 12.7a and b shows
varying abdominal positions of an appendix.
Examples of different anatomical locations of both
the appendix and ICV are presented in Chap. 11.
As discussed in Chap. 11, we need to be aware of
extrinsic impressions on the colon lumen due to
structures that lie adjacent to the colon.
Figure12.8 (i) and (ii) shows an extrinsic impression on the colon lumen caused by spondylolisthesis. A range of extrinsic impressions on the
colon are presented in Chap. 11.
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J. H. Bortz
ab
Fig. 12.7 (a) Sagittal 2D view showing pre-vertebral appendix (white arrow). (b) Coronal 2D showing malrotated
caecum (C) with appendix (white arrow)
(i) (ii)
Fig. 12.8 (i) 3D view of sigmoid colon showing extrinsic soft tissue bulge (arrows) due to spinal spondylolisthesis. (ii).
Sagittal 2D grade 2 spondylolisthesis of L5 on S1. This is associated with disc degenerative disease between L5 and S1
12.2.7 Position oftheCatheter
The position of the rectal catheter can impact on
evaluating the anorectal region [9]. Occasionally,
the rectal catheter may be inserted too far into the
rectum with the result the tip then projects beyond
the superior valve of Houston. Although this is
easily identied, sometimes when ying from the
caecum to the rectum the catheter’s tip may
assume the shape of a polyp as shown in
Fig. 12.9a (i) and (ii). Another example of this
pitfall is when the tip of the catheter comes into
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a(i) a(ii)
b(i) b(ii)
159
c
Fig. 12.9 (a) (i) 3D view showing catheter tip simulating
a polyp (arrows). (ii) 3D view showing catheter tip simulating a polyp (arrow). (b) (i) 3D view showing catheter
tip distorting fold (open black arrow). Rectal catheter=C.
(ii) Sagittal 2D view showing tip of catheter (C) extending
beyond the middle valve of Houston (green arrow).
Superior valve of Houston (yellow arrow). (c) Meniscus
sign (arrow)
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J. H. Bortz
contact with the superior valve of Houston and
causes an extrinsic impression on the mucosa as
evident in Fig.12.9b (i) and (ii).
The author’s standard technique is to perform
a 360° y around the rectal catheter to ensure
adequate visualisation of all surrounding features. This technique also reduces the chances of
a polyp being missed due to it being obscured by
the rectal catheter as discussed in Chap. 13.
To keep the catheter in position in the rectum,
it is essential to inate the balloon, but as discussed in Chap. 13 pathologies, such as internal
haemorrhoids, may be obscured. To visualise
compressed haemorrhoids, it is essential that the
balloon is deated when the patient is in the
prone position (see Chap. 13). Furthermore, an
inated balloon may cause a defect called the
meniscus sign [1]. Figure12.9c demonstrates this
defect. The meniscus sign is also discussed in
Chap. 13.
12.2.8 Movement Artefacts
breathing, patient movement, spasm, or beam
hardening, is created. It is best seen on 2D views
where the artefact is most prominent [11]. It may
occur in the sigmoid colon, descending colon,
transverse colon, ascending colon, and caecum
(Fig. 12.11a–g (ii)). This artefact may also be
seen on abdominal multidetector CT (MDCT)
studies [10]. It occurs in approximately 25% of
studies but does not usually obscure pathology.
It may however potentially obscure pertinent
CTC ndings [10].
12.2.9 Beam Hardening Artefacts
Dark streaks are produced by beam hardening as
well as scatter. Both produce dark streaks. These
streaks are between two high attenuation objects,
for example, metal or bone, with surrounding
bright streaks [3]. Examples include unilateral or
bilateral hip replacements, and surgical clip artefacts. Examples of beam hardening artefacts are
presented in Fig.12.12a (i)–e.
It is essential that patients co-operate during CTC
examinations (see Chap. 2). Adequate breath
holding during scanning is essential [4]. For all
scans, instruct the patient to inhale, then exhale,
and suspend breathing during scanning. Breathing
during scanning causes artefacts as evident in
Fig.12.10(i)–(iii). Technological advances in CT
imaging have resulted in very short scanning
times which also reduce risk of movement artefacts. Patients should not move during scanning
to prevent movement artefacts.
12.2.8.1 ‘Dense Waterfall’ Sign
The ‘dense waterfall’ sign is an artefact that is
not related to voluntary patient movement or
breathing. It was rst described by Boyce etal.
[10] in 2012. It is a luminal artefact, which
occurs when opacied luminal uid ows from a
higher to a lower level relative to the patient
position on the scanner table. It is caused by the
CT scanner catching the movement of the opacied uid at a moment in time. A distinctive arciform artefact, which is not due to patient
12.2.10 Ingested Artefacts
It is important for patients to follow instructions
as discussed in Chap. 2. Bowel preparation commences the day before the scheduled examination and a 24h liquid diet is required (see Chap.
9). An ingested vitamin tablet may resemble a
polyp (Fig.12.13a). Oil capsules (e.g., omega 3)
do not always dissolve; they may remain intact in
the gastrointestinal tract for a period of time. The
same applies to softgel long-acting cold and u
capsules. Both types of capsules may resemble a
polyp particularly on a 3D display.
Figure 12.13b(i)–(iii) presents examples of an
ingested sh oil capsule. These foreign objects
do not adhere to the bowel mucosa and move
with postural change. Furthermore, the internal
attenuation of these ingested artefacts is very different from a polyp. According to Yee [2], we
must also be aware of ingested vegetable matter,
such as corn and seeds, as they too can be confused with polyps.
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(i) (ii)
(iii)
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Fig. 12.10 (i) 2D axial view showing focal motion arte-
fact in the descending colon (arrow). Rest of colon is normal. (ii) Example of a breathing stepped artefact (arrows).
(iii) Sagittal 2D showing breathing artefact on skin surface (arrows)
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J. H. Bortz
d(i) d(ii)
Fig. 12.11 (a) 2D axial view showing the arciform arte-
fact of the ‘dense waterfall’ sign (DWS) in the sigmoid
colon (open green arrows). (b) 2D axial view showing the
arciform artefact from the DWS in the sigmoid colon. (c)
(i) 2D axial showing the DWS in the sigmoid colon (open
black arrows). (ii) 3D endoluminal view showing the artefact caused by the DWS (open black arrows). (d) (i) 2D
axial view showing the DWS (black arrows). (ii) 3D endoluminal view showing the artefact caused by the DWS
(open black arrows).
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d(iii) e
f(i) f(ii)
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g(i) g(ii)
Fig. 12.11
artefact (white and open black arrows). (e) 2D axial view
showing the alternating dark and light appearance of the
DWS artefact in the transverse colon (open black arrows).
(f) (i) 2D axial showing DWS (open black arrows) in the
ascending colon. K kidneys, A aorta. (ii) 3D endoluminal
(iii) Translucent display showing contrast uid
view showing the artefact caused by the DWS (open black
arrow). (g) (i) 2D axial showing the DWS artefact in the
ascending colon (open black arrow). K kidneys, A aorta.
(ii) 3D endoluminal view showing the artefact caused by
the DWS (open black arrow)
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a(i) a(ii)
b c(i)
J. H. Bortz
Fig. 12.12 (a) (i) Beam hardening artefact (arrows) due
to right hip prosthesis. (ii) Axial 2D showing streak artefact (arrows) due to right hip prosthesis. (b) Axial 2D
showing streak artefact (arrows) due to bilateral hip prostheses. (c) (i) Streaks due to beam hardening artefact
(arrows).
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