s. kouki, m. attia, m. landoulsi, s. bouguerra, y. arous, h. boujemaa, n. ben abdallah...
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S. KOUKI, M. ATTIA, M. LANDOULSI, S. BOUGUERRA,
Y. AROUS, H. BOUJEMAA, N. BEN ABDALLAH
VALUE OF VIRTUAL COMPUTED TOMOGRAPHIC COLONOGRAPHY
FOR COLIC LESIONS
GASTROINTESTINAL RADIOLOGY : GI 10
Virtual colonoscopy is a promising new technique that combines rapid spiral CT scanning of the abdomen with advanced computer programs capable of re-creating two- and three-dimensional views of the colon and rectum.
The purpose of our study was to determine the usefulness of a virtual computed tomography colonoscopy for the detection of colic lesions.
Introduction
Fifteen patients were evaluated with computed tomography colonoscopy using 64-row MDCT.
CT images were analyzed by the colon dissection workup with unfolded haustra visualization and also using the virtual colonoscopy technique (axial images and endoluminal views).
Materials and methods
A clean well prepared and adequately distended colon is a prerequisite for a high quality CTC examination.
Patients need to undergo a 24-h colonic preparation similar to that required for colonoscopy and direct contrast barium enema.
This usually involves adherence to a clear liquid diet for 24 h and the ingestion of a laxative the day before.
Polyethylene glycol results in relatively larger amounts of residual fluid and is less suitable for this procedure.
Cathartics, for example sodium phosphate and magnesium citrate, produce a ‘‘dry prep’’ with little fluid left behind and are the preferred agents.
Preparation
CT virtual colonoscopy was performed with a 64-slice CT
scanner (GE).
On the insertion of a rectal enema tube, the patients colon was
then insufflated with room air based on the patients tolerance.
The catheter was clamped and a single scout view was
obtained to verify bowel distention.
Additional air was insufflated into the rectum if inadequate
distention of the colon was observed.
Once colon distention was adequate, CT scans were performed
from the diaphragm to the pubis, with the patient in both
supine and prone positions.
The actual procedure takes about 10 min
Computed tomography virtual colonoscopy
The two CT data sets were transferred to a workstation.
Images were analyzed using the conventional virtual
colonoscopy technique evaluating both the 2D transverse
images and the 3D reformatted virtual endoscopic images,
performing a virtual ‘‘fly-through’’ path of the colon.
CT image processing and analysis
Image processing and interpretation are done using specialized
software.
The software extracts the images from the air-filled colon and
removes the impression of the opacified residual fluid.
In addition, the system creates a centerline through which the
colonic lumen can be navigated.
A trained radiologist takes about 20 min to evaluate the final images.
CT image processing and analysis
All our patients had incomplete colonoscopy .
Eight patients consulted for rectal bleeding and seven had
bowel dysfunction and abdominal pain.
10 patients presented with a colonic lesion at CT colography.
In detail, three cases of colorectal cancer, three cases of
polyps, one case of right colon diverticula with stigmata of
hemorrhage, one case of right colon tuberculosis, one case of
ischemic lesion of the sigmoid colon and one case of extrinsic
compression of the left colon by a gastric stromal tumor.
Results
Patient N°1 60 year- old old man Rectal bleeding Incomplete colonoscopy
Oblic reformattedCT image clearly shows a neoplasic mass of the right colon Three-dimensional similar barium
enema image show an excentric narrowing of colonic lumen
Patient N° 1
Reformated CT images show a mass of the right colon with enlarged lymph node and infiltration of pericolic fat
Patient N°2 58 year-old man Bowel impairment Incomplete colonoscopy
Reformatted CT images showing ahuge neoplastic mass (arrow),well recognisable as hypodensemass within the colonic lumen
PatientN°2
Threedimensionalthreshold renderedendoluminal CT colonographshows a similar endoscopicappearance of the mass
Three-dimensional similar barium enema imageShowing an excentric narrowing of colonic lumen
Patient N°3 47 right iliac fossa pain.
Bowel impairment
Incomplete colonoscopy
Reformated CT images show a circumferential thickening of the colonic wall with mesenteric fat infiltration.colonic biopsy : tuberculosis
Three-dimensional similar barium enema image showing a tight circumferential stricture of the right colon
Patient N°460 year-old manRectal bleedingIncomplete
colonoscopy
Axial CT scanthe presence of diverticular orifices (arrows) with stigmata of recent bleeding
Three-dimensional threshold rendered endoluminalvirtual dissection of sigmoid colon shows the presence of diverticular orifices (arrows)
Three-dimensional threshold rendered endoluminalvirtual dissection of sigmoid colon shows the presence of a sessile polypoid lesion
Patient N°5
Three-dimensional threshold rendered endoluminalvirtual dissection of the colon showing an extrinsic compression by a gastric stromal tumor
Three-dimensional similar barium enema image showing an extrinsic compression by a gastric stromal tumor
Patient N°6
tight circumferential stricture of the sigmoid colon : ischemic lesion of the sigmoid colon
Patient N°770 year-old manhistory of colic
polyposis.incomplete colonosc
opy
Oblic reformattedCT image clearly shows a polyp lesion in the sigmoid colon.
endoluminal CT colonographicview (confirm the diagnosis of the sigmoid polyp.
Computed tomography virtual colonoscopy is a new
generation technique for colorectal evaluation by using
high resolution, thin section volumetric CT data of the air
distended, clean colon.
Since the first description of the technique by Vining et al
in 1994, new developments in CT equipments and virtual
colonoscopy postprocessing softwares have been
accomplished, and the diagnostic accuracy of the
procedure, even for the detection of colonic lesions smaller
than 5 mm, has improved.
Discussion
It is important to emphasize that virtual colonoscopy is an
operator-dependent method that needs a steep learning
curve and adequate training.
It was been demonstrated in several reports that the
combination of 2D, 3D and endoluminal images
significantly increases the sensitivity and specificity of the
method.
Discussion
An adequate bowel cleansing facilitates a rapid and
accurate evaluation of the colon.
The presence of stool or fluid retention prevents the
software identifying the true path and creates the right
centerline.
To overcome the problem, the software creates in those
areas, bridges containing no diagnostic information.
Discussion
Currently, one of the major drawbacks of CT colonography
is the long evaluation time.
Its main advantages compared with the conventional
virtual colonoscopy analysis are:
- it is a non-invasive technique.
- it obviates the need for sedation
- this technique does not require ante- and retrograde
viewing because an almost complete surface visibility is
already obtained in a single direction way
Discussion
CTC has proved to be a useful modality in the following
conditions:
1 Failed colonoscopy;
2 Evaluation of the colon proximal to an obstructing lesion
3 CRC screening in patients with contraindications to
colonoscopy or who refuse optical colonoscopy;
4 Patients with coagulaopathy, intolerance to sedation, and
who refuse other screening options.
Main indications
CT colonography or virtual colonoscopy is a fairly new
modality that has the potential to play a significant role in
screening for colic lesions.
Virtual colonography is a reliable non-invasive , well-
tolerated method, with high specificity and sensitivity for
the visualization of the entire colon, even in sites that are
inaccessible to conventional colonoscopy.
Conclusion
CT colonography with reduced bowel preparation after incomplete colonoscopy in the elderly. F. Iafrate and al. Eur Radiol (2008) 18: 1385–1395.
Multidetector CT colonoscopy: evaluation of the perspective-filet view virtual colon dissection technique for the detection of elevated lesions. Patricia Carrascosa and al. Abdom Imaging (2007) 32:582–588.
Screening of patients after colectomy: virtual colonography. P. Leonardou and al. Abdom Imaging (2006) 31:521–528.
Virtual colonoscopy: issues related to primary screening. Perry J. Pickhardt. Eur Radiol Suppl (2005) 15[Suppl 4]:D133–D137
REFERENCES
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