16.1
Introduction
Currently, there are two main indications for CT
colonography (CTC). The fi rst is polyp detection in
patients who have an increased risk for colorectal
cancer or for screening purposes in asymptomatic
patients who are at average risk. The second common
indication is incomplete or failed colonoscopy, where
CTC is useful for complete colon visualization; for
example, to detect additional lesions proximal to a
stenotic cancer ( M orrin et al. 1999; M acari et al.
1999 ; C opel et al. 2007) . In addition to these main
indications, there are several other situations where
the role of CTC is not yet clearly defi ned. Some of
these conditions may lead to colon obstruction, in
which case, CTC is performed after incomplete
colonoscopy. However, CTC may also be used for sur-
veillance of these conditions, as an alternative
to colonoscopy or barium enemas. Diverticular dis-
ease is the most common colonic disease in the
Western world and often leads to diverticulitis. CTC
is helpful in the assessment of not only the lumen,
but also of any extramural changes (Table 16.1 ).
Recent reports indicate a higher risk of colonic per-
foration in acute infl ammatory conditions with CTC
(C oady -F ariborzian et al. 2004 ; B urling et al.
2006 ; T riester et al. 2006 ; W ong et al. 2007) . At
chronic stages of infl ammatory bowel disease (IBD),
CTC can provide information about the extent of the
disease, stenosis and pre-stenotic regions, as well as
about the extracolonic extent and complications of
the disease (R egge et al. 2009) .
Although recent guidelines do not consider CTC
as a surveillance option, a few recent studies have
suggested its usefulness in post-surgical colorectal
cancer surveillance ( Fletcher et al. 2002 ; Laghi
et al. 2003 ; Leonardou et al. 2006 ; You et al. 2006) .
T. Mang, MD
W. Schima, MD, MSc
A. Maier, MD
P. Pokieser, MD
Department of Radiology , Medical University of Vienna ,
Waehringer Gürtel 18–20 , 1090 , Vienna , Austria
Virtual Colonoscopy: Beyond Polyp Detection 16
T. Mang , P. Pokieser, A. Maier, and W. Schima
C O N T E N T S
16.1 Introduction 199
16.2 Diverticular Disease 200
16.3 Infl ammatory Bowel Disease 202
16.3.1 Ulcerative Colitis 204
16.3.2 Crohn’s Disease 206
16.4 Colorectal Carcinoma 207
16.5 Colorectal Lymphoma 211
16.6 Surveillance Post-Surgery
or Post-Intervention 213
References 216

200 T. Mang, P. Pokieser, A. Maier et al.
There is little experience about the feasibility of CTC
in the evaluation of colonic lymphoma or post-inter-
ventional surveillance.
Although the primary target lesion for CTC is
defi ned as the advanced adenoma, CTC is able to pro-
vide unique information about many other patho-
logical conditions.
16.2
Diverticular Disease
Diverticular disease is the most common colonic dis-
ease in the Western world, affecting 10–30% of peo-
ple at the age of 50 years and 30–60% at the age of 80.
However, the disease is asymptomatic in the majority
of patients. Together with aging, long-standing low
fi ber diet is the main predisposing factor for diver-
ticular disease. Other etiological factors have been
suggested, including increased consumption of red
meat, fat, and salt.
The initial stage of the disease is the so-called pre-
diverticulosis, which is characterized by thickening
of the muscular layer, shortening of the taeniae, and
luminal narrowing (Fig. 16.1a, b ). With advancing
disease, caliber and haustral abnormalities appear.
This results in a continuous wall thickening of
>4 mm, of long colonic segments with prominent
semicircular folds, shortened interhaustral segments
(concertina appearance), and a reduced colonic
distensibility ( Lefere et al. 2003) (Fig. 16.2a–d )
Histologically, most of the diverticula are pseudo-
diverticula, which are herniations of the mucosa and
submucosa, through the circular muscularis propria
layer at weak points in the colonic wall where nutri-
ent arteries penetrate the muscularis propria. Rarely,
true diverticula (most often at the proximal colon)
are found, which are characterized by an outpouch-
ing of all wall layer (ie., mucosa, submucosa, and the
muscularis propria). The radiological features of the
two types of diverticula are not distinguishable. The
CTC appearance of diverticula is easily recognized as
air-fi lled outpouchings of the colonic wall on 2D
images. On virtual endoscopic (VE) images, the
diverticular orifi cium can be recognized as a com-
plete dark circumferential ring when seen en face .
Because of the complete dark ring, diverticula may
simulate polyps when seen en face on VE images
(F enlon et al. 1998) (Fig. 16.3a, b ).
Diagnostic problems can occur if a diverticulum
inverts into the colonic lumen or is impacted with
stool. A diverticulum may occasionally invert into
the colonic lumen and produce a pseudopolypoid
lesion on 2D and 3D images. The corresponding VE
image is nonspecifi c and shows a polypoid lesion
(Fig. 16.4a, b ). The 2D images are pathognomonic to
arrive at the correct diagnosis. Inverted diverticula
with a pseudopolypoid shape sometimes contain fat
Table 16.1. CTC features of diverticular disease
Diverticula
Gas-fi lled outpouching of colon wall in 2D
Complete dark ring in 3D
Cave: polypoid pseudolesion in VE “ en face ”
Impacted diverticula
Polypoid pseudolesion in 3D
Incomplete ring shadowing in 3D
2D pathognomonic: fi lled with air, stool, retained
barium, CM wall enhancement
Diverticulitis
Wall thickening with CM enhancement
Stenosis and pericolic fat stranding
VE: nonspecifi c
Fig. 16.1. Pre-diverticulosis.
( a ) Axial plane and ( b ) vir-
tual endoscopic (VE) shows
prominent semicircular
folds, shortened interhaus-
tral segments (concertina
appearance), and a reduced
distention of the sigmoid
colon. ( b ) VE shows a single
diverticulum ( arrow )
a b