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11 Anatomy oftheColon: Rectum toIleocaecal Valve
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(i) (ii)
Fig. 11.13 Mobility of segments (i) Supine colon-map. Caecum (C) and rectum (R); (ii) Prone colon-map shows dif-
ferent positions of caecum (C). Rectum (R)
11.5 Extrinsic Impressions
Any structure that lies adjacent to the colon may
cause an extrinsic impression on the colon lumen
[17]. An extrinsic impression may present as a
submucosal lesion and cause problems, particularly during optical colonoscopy. These impressions are easily identiable when 2D MPR is
performed. The most common sources of these
impressions include the kidneys, aorta and iliac
arteries, uterus and adnexa, and adjacent gastrointestinal tract (GIT), such as the small bowel.
The ‘continuous fold’ sign occurs when a structure, which is causing the extrinsic impression,
displaces but does not efface the overlying
colonic fold. Figure 11.14a (i)–g (ii) are examples of extrinsic impressions on 3D and 2D
images.
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a(i) a(ii)
b(i) b(ii)
J. H. Bortz
Fig. 11.14 Extrinsic impressions. (a) (i) 3D view of an
extrinsic impression (circle) on bowel caused by the aorta;
(a) (ii) 2D axial view shows aorta causing external impression on colon (open white arrow). (b) (i) 3D view of
spleen (circle) causing an extrinsic impression on colon;
(b) (ii) 2D axial view shows an extrinsic impression (open
white arrow) on colon caused by the spleen (S). Aorta (A);
right and left kidneys (RK and LK).
11 Anatomy oftheColon: Rectum toIleocaecal Valve
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147
c(i)
c(iii)
c(ii)
d(i)
Fig. 11.14
on colon due to a renal cyst (circle); (c) (ii) 2D sagittal
view shows renal cyst in lower pole of right kidney
impinging on the caecum (C); (c) (iii) 2D coronal view
(c) (i) 3D view showing extrinsic impression
shows extrinsic impression of lower pole of kidneys (open
white arrows) on colon. RK right kidney, LK left kidney, L
liver, S stomach. (d) (i) 3D view shows psoas muscle
extrinsic impression (open black arrows) on colon;
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d(ii) e(i)
e(ii) f(i)
J. H. Bortz
Fig. 11.14
muscles (P) indenting bowel (open white arrows). (e) (i)
3D view showing extrinsic impression by small bowel
(circle); (e) (ii) 2D axial view shows extrinsic impression
(d) (ii) Prone 2D axial view showing psoas
of small bowel (open white arrow) on colon. (f) (i) 3D
view shows extrinsic impression of uterine broid
(arrows). Rectal catheter (C);
11 Anatomy oftheColon: Rectum toIleocaecal Valve
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f(ii) g(i)
g(ii)
149
Fig. 11.14
broid (F) causing narrowing of rectum (open white
arrow). (g) (i) 3D view shows a rib causing extrinsic
(f) (ii) 2D axial view of a pedunculated uterine
11.6 Salient Points ofCTC
Anatomy
The following needs to be considered when interpreting CTC images.
• The position of the rectum and valves of
Houston and normal variants.
• The rectosigmoid junction has a loosely
attached mesentery which allows for mobility;
it may be redundant in some people.
• The descending colon is relatively xed; its
folds are circular in appearance.
• The transverse colon’s folds are triangular in
appearance; it has a loose mesenteric attach-
impression (circle); (g) (ii) 2D axial view of a rib causing
extrinsic impression (open red arrow)
ment and it often changes in position with
postural change during a 2-view CTC study.
• The ascending colon has triangular folds.
• The ileocaecal valve (ICV) is constant relative
to the terminal ileum and caecum; its
appearance varies from a labial type to a more
bulbous polypoidal/papillary type; it may be
open or closed during a CTC study; it has a
central depression or ‘pit’ orice where the
terminal ileum empties into the right colon.
• The caecum is proximal to the ICV; it may be
mobile and displaced.
• The vermiform appendix is part of the caecum; its intra-abdominal position may vary
widely due to mobility of the caecum.
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J. H. Bortz
• Extrinsic impressions (caused by structures
adjacent to the bowel) may be present on the
colon lumen.
11.7 Summary
Knowledge of normal anatomy of the colon, its
variants, and extrinsic impressions on it, is essential for correct interpretation of 2D and 3D CTC
images. Malrotation and mobility of some segments of the colon may be evident in CTC studies. Mobile segments may change position during
a standard 2-view CTC study: supine and prone
scans.
References
1. Muto T, Bussey HJR, Morson BC. The evolution of cancer of the colon and rectum. Cancer.
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2. Pickhardt PJ.Screening CT colonography: how I do
it. AJR. 2007;189(2):290–8. https://doi.org/10.2214/
ajr.07.2136.
3. Yee J.Virtual colonoscopy. Philadelphia: Lippincott,
Williams & Wilkins; 2008. p.123–4.
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org/10.1136/gutjnl- 2014- 308696.
5. Bortz JH. CT colonography: an approach for a successful examination. S Afr J Rad. 2014;18(1):607, 11
pages. https://doi.org/10.4102/sajr.v18i1.607.
6. Regge D, Monica PD, Galatola G, et al. Efcacy
of computer-aided detection as a second reader for
6–9mm lesions at CT colonography: multicenter prospective trial. Radiology 2013; 266 (1): 168–176.
7. Halligan S, Mallett S, Altman DG, etal. Incremental
benet of computer-aided detection when used as a second and concurrent reader of CT colonographic data:
multiobserver study. Radiology. 2011;258(2):469–76.
https://doi.org/10.1148/radiol.10100354.
8. Netter F.The Ciba collection of medical illustrations,
vol 3. Digestive system. Part 2. Lower digestive tract.
NewYork: Colour Press. 1962. pp.54–63.
9. Hamilton SR. Structure of the colon. Scand J
Gastroentrol Suppl. 1984;93:13–23.
10. Abramson DJ.The valves of Houston in adults. Am J
Surg. 1978;c136:334–6.
11. Ahmed I, Asgeirson K, Beckingham I, Lobo D.The
position of the vermiform appendix at laparoscopy. Surg Radiol Anat. 2007;29:165–8. https://doi.
org/10.1007/s00276- 007- 0182- 8.
12. Varsamis N, Pouggouras K, Salveridis N, et al.
Appendiceal intussusception. In: Lulu G, editor.
Current concepts in colonic disorders, 2012. pp.47–64.
[cited 2022 October 30]. http://www.intechopen.
com/books/current- concepts- in- colonic- disorders/
appendicealintussusception.
13. Strouse PJ. Disorders of intestinal rotation and xation (“malrotation”). Pediatr Radiol. 2004;34:837–51.
https://doi.org/10.1007/s00247- 004- 1279- 4.
14. Torres AM, Ziegler MM.Malrotation of the intestine.
World J Surg. 1993;17:326–31.
15. Pickhardt PJ, Bhalla S.Intestinal malrotation in adolescents and adults: spectrum of clinical and imaging
features. AJR. 2002;179(6):1429–35.
16. Maxson RT, Franklin PA, Wagner CW.Malrotation in
the older child: surgical management, treatment, and
outcome. Am Surg. 1995;61(2):135–8.
17. Pickhardt PJ, Kim DH.CT colonography: principles
and practice of virtual colonoscopy. Philadelphia:
Saunders; 2009.
CTC Traps andArtefacts
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JoelH.Bortz
12
12.1 Introduction
It is important when interpreting both intracolonic
and extracolonic images to be familiar with the
normal appearance of all structures. We need to be
familiar with normal CTC images in order to recognise potential traps (pitfalls) that could impact
on image interpretation [1, 2]; at times one can be
misled by artefacts [3] that could be mistaken for
pathology. In this chapter, the importance of being
aware of potential traps and artefacts at CTC
interpretation is underscored with examples.
12.2 General Principles
Prominent folds and shifting of pedunculated
polyps present more of a problem on 2D than 3D
interpretation. Figure12.1 (i–iv) is an example of
complex folds. Submucosal lesions and stool
lled diverticula become more of an issue on
3D. However, the complementary nature of 2D
(two-dimensional) and 3D (three-dimensional)
evaluation usually resolves these issues. The
below 12 broad groups of potential traps, including artefacts, are the focus of this chapter.
• cathartic preparation and tagging solutions
• sigmoid diverticular disease
• polyp morphology
• anatomical locations and structures
• external impressions of organs and bony
structures on the colon
• position of the catheter
• movement artefacts
• beam hardening artefacts
• ingested artefacts
• electronic cleansing
• mucus strand
• tampon and vaginal pessary
Artefacts are unwanted features on a CTC
image that may obscure or simulate pathology
[3]. The above groups are discussed with examples. The following abbreviations are used in this
chapter.
• 2D: two-dimensional
• 3D: three-dimensional
• ICV: ileocaecal valve
• MDCT: multidetector CT
• OC: optical colonoscopy
• RLD: right lateral decubitus
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_12
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(i) (ii)
(iii) (iv)
J. H. Bortz
Fig. 12.1 (i) Bid fold (arrow). (ii) Two folds (a and b) joining to form a single fold (c). (iii) Mild twisting of haustral
fold (arrows). (iv) Shortened and thickened fold (arrow)
12.2.1 Cathartic Preparation
andtheUse ofTagging
Solutions
Bowel preparation and the use of tagging solutions are discussed in Chap. 9. We need to be
aware of potential traps that may be caused by
poor bowel preparation in terms of
1. retained stool
2. different appearances of stool and its
characteristics
3. movement of stool during postural change, for
example, supine to RLD or prone positions
[4]
In order to differentiate a polypoidal lesion
from stool there are clues available: 2D and 3D
viewing are complementary [4]. The former is
the most useful method to make the distinction.
Stool may be covered by barium and frequently
contains small bubbles of air giving it a heterogeneous appearance (Fig.12.2a). Air within stool is
not identied on 3D viewing. Most typically
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153
a
b(i)
b(ii)
Fig. 12.2 (a) 2D axial view showing air in stool. (b) (i) 2D axial supine showing stool (open red arrow). (ii). 2D RLD
view showing movement of stool (red arrow)
stool will move to the opposing wall when the
patient is turned from the supine to the prone, or
RLD position. Figure 12.2b (i) and (ii) shows
movement of stool between supine and RLD
position.
squared, or faceted in appearance; it may occasionally be confused with a large villous lesion.
Bulky stools are usually mobile and on translucent display (TD) may reveal mottled low- density
lesions. Figure12.3a (i)–d (ii) shows a range of
examples of stool being a potential interpretation
12.2.1.1 Retained Faecal Matter
In order to visualise colon anatomy, it is necessary for the bowel to be clean [4, 5]. This entails
the use of a cleansing regimen that patients must
follow prior to the study to eliminate bulky stool
from the colon (see Chap. 9). Most cathartic
agents enable bowel cleansing to occur. However,
small particles of adherent stools may remain on
the colon wall and may mimic a sessile polyp. It
is easier to identify large bulky stool that sometimes remain. The shape may be polypoidal,
trap.
Tagging is an integral part of colonic preparation [4]. Barium tags any remaining stool
adherent to the bowel lumen which usually
allows for easy distinction between stool and
polyps [6]. Software systems that include a TD
function (such as Viatronix) display barium as
white [4].
Tagging agents Gastrogran and Omnipaque
(see Chap. 9) have a dual action. They stain the
residual uid white thus aiding in 2D evaluation
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J. H. Bortz
of submerged polyps as well as emulsifying the
12.2.2 Electronic Cleansing
stool adherent to the bowel wall thus causing a
secondary catharsis [6]. They provide further
internal tagging of solid debris. In a small percentage of cases, the mucosa, particularly in the
caecum and ascending colon, may have adherent
stool on the surface. We use 2D to evaluate adherent stool seen in this area of the colon: it is
quicker and more accurate than 3D.Figure12.3e
shows adherent stool.
During a CTC examination, faecal matter may
obscure lesions. Electronic cleansing marks the
stool that has been tagged. The stool is then
removed electronically [7]. This method does
produce cleansing artefacts. Figure12.4a (i) and
(ii) illustrates before and after electronic cleansing of the colon. As described in Chap. 9, bowel
preparation includes the use of tagging.
a(i) a(ii)
b(i) b(ii)
Fig. 12.3 (a) (i) 3D endoluminal view showing lobulated
polypoidal lesion (circle). (ii) TD conrming stool (open
black arrow) and not a polyp. (b) (i) 3D view showing
polypoidal lesion on haustral fold (open black arrow). (ii)
2D axial showing stool (open white arrow). RK right kidney, LK left kidney, A aorta. Small amount of atherosclerotic calcication on posterior wall of aorta (black arrow).
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