Defining the Patient Preparation and CT Technique

The effect of preparation is important, not only in terms of cleansing of the colon of residual stool, but also of residual fluid. Most CTC reports have been done on consenting research patients who are already scheduled to undergo a non-research conventional colonoscopy. The preparation is often chosen by the gastroenterologist. A colonic lavage with 4 L of polyethylene glycol is know to leave significant residual fluid which can hide polyps unless a unique strategy is used to reveal polyps...

Hemorrhoids

Internal hemorrhoids can be seen as smoothly marginated and curved filling defects that project into the rectal vault, lying adjacent to the rectal tube tip (Fig. 14.1). In contradistinction, low rectal cancers will normally have shouldering, and arise some distance from the anus itself. Physical examination usually confirms the presence of internal hemorrhoids. If the remainder of the colorectum has been cleared of significant lesions, a limited proctoscopic or sigmoidoscopic examination can...

Economical Impact

Hara et al. (Hara et al. 2000) reported that the additional and recommended work-up added 28 to the examination cost per patient. If all highly important lesions would be further investigated, the added costs would be 36 per patient. Gluecker (Gluecker et al. 2003) reported an added costs of 34 to the average cost. Given the fact that in truly screening patient populations the total number of highly suspected findings is expected to be lower, as shown by Pickhard (Pickhard et al. 2003), both...

Mucous Filaments

Mucous filaments appear as thin threadlike structures crossing the colonic lumen or lying upon one or more semicircular folds. They can occur after a preparation without or with faecal tagging. In the latter case these filaments can be tagged or non-tagged. They can changed in shape with dual positioning. However they may simulate the stalk of a polyp. It is important not to misinterpret it as a polyp and vice versa. In the latter case they are not connected to the head of a polyp. However...

Intravenous Spasmolytics

There are two intravenous spasmolytics available for CT colonography hyoscine butylbromide and glucagon hydrochloride. Both produce hypotonia in smooth muscle within the colonic wall and are used widely to improve distension during double contrast barium enema. However, while both agents have been shown to improve patient perception during barium enema, only hyoscine butylbromide reliably improves distension (Goei et al. 1995 Bova et al. 1993). As a result, it is widely utilized for barium...

Absolute Contraindications

Many CT scanners have a weight limit of 300 to 400 pounds and a circumferential girth limit of 60 cm. A patient with an acute abdomen should not be inflated with room air or CO2, and a consultation with a surgeon is most appropriate. Patients with active diverticulitis should not be referred to CT colonography. If an abscess or free air is suspected, a CT of the abdomen and pelvis can be performed with oral and IV contrast. Insufflation of the colon is contraindicated and may cause perforation...

References

Barish MA, Soto JA, Ferrucci JT (2005) Consensus on current clinical practice of virtual colonoscopy. Am J Roentgenol 184 786-792 Bromer MQ, Weinberg DS (2005) Screening for colorectal cancer - now and the near future. Semin Oncol 32 3-10 Callstrom MR, Johnson CD, Fletcher JG et al. (2001) CT colonography without cathartic preparation feasibility study. Radiology 219 693-698 Cotton PB, Durkalski VL, Pineau BC et al. (2004) Computed tomographic colonography (virtual colonoscopy) a multicenter...

How to Interpret the Data Sets

7.2 Current and Future Image Display Techniques 73 7.2.1 2D Multiplanar Reformation (2D MPR) 74 7.2.2 3D Endoscopic Fly-Through 75 7.2.3 3D Transparency View (Edge-Enhanced View) 76 7.2.4 Future Advances in Image Display Techniques 76 7.3 Different Categories of Colorectal Morphologies 76 7.3.1 Focal Polypoid Lesions (r o stool) 76 7.3.4 Advanced Mural Lesions (r o collapse) 81 7.4 Standardization of Reporting of Clinically Significant Colorectal Findings 82 References 85 CT colonography (CTC)...

Introduction

The importance of achieving optimal colonic distension prior to CT colonography cannot be overstated, and the editors have justifiably devoted an entire chapter to the subject. Optimal luminal distension enables the reader to rapidly and confidently assess the colon, and undoubtedly improves diagnostic accuracy (Chen et al. 1999 Fletcher et al. 2000 Yee et al. 2003). Conversely inadequate distension may obliterate the colonic lumen and results in wall haustral fold thickening (Fig. 5.1) thereby...

CAD Techniques for Detection of Polyps

To date, most of the CAD schemes developed in academia and in industry comprise of the following four fundamental steps (1) extraction of the colonic wall from the CTC images, (2) detection of polyp candidates in the extracted colon, (3) characterization of false positives, and (4) discrimination between false positives and polyps. A brief descrip tion of each of these steps is provided below. More technical details on the fundamental CAD scheme can be found in recent review articles (Yoshida...

Colonic Distension

Proper distension of the colon is necessary to allow the radiologist the ability to visualize polyps and cancers that may impinge upon the lumen on CT colonography (Figs. 3.5, 3.6). A segment of colon that is poorly distended or collapsed can simulate a malignant narrowing such as that caused by an annular carcinoma (Fig. 3.7). A well-trained technologist or nurse can assist in placing the rectal tube with care and performing the colonic insufflation, depending upon local guidelines. With the...

Colorectal Carcinoma

Adenocarcinomas are the most common colonic primary tumors. The peak incidence is between 50 and 70 years of age. Approximately 90 arise from benign adenomatous polyps. Most carcinomas show an exophytic, polypous type of growth with frequent central degeneration. Adenocarcinomas tend to infiltrate the bowel wall circumferentially and 50 are found in the rectum, and 25 in the sigmoid. In up to 5 of cases, a synchronous carcinoma is present (Fig. 13.18a,b). The main indication for CT colonography...

Stool

Stool is the most frequent cause of false positive findings at CT colonography (Fletcher et al. 2000). There are several imaging characteristics, which usually aid in the identification of stool. Stool has a heterogeneous internal attenuation, often with internal air (Fig. 14.16). Additionally, stool particles usually lie along the dependent colonic wall and change location with changes in patient positioning (Fig. 14.17). On 3D normal endoluminal images, Fig. 14.14a-c. Lipoma. Note the...

Conclusion and Future Development

Three-dimensional display is an integral part of reviewing of CT-colonography examinations and most likely a prerequisite for good sensitivity. The method can be used either primary or as adjunct to 2D evaluation. In populations with a high polyp prevalence the use of primary 3D does not seem advantageous compared to primary 2D, although comparative data are sparse and no optimized 3D methods have been used. The use of the later methods might prove to be valuable. The question which review...

Collapse and Contraction

Contraction Colon

Luminal collapse can be confused with malignant scirrhous tumors by radiologists learning CT colo-nography (Fidler et al. 2004). Imaging patients in two positions has been shown by multiple observers to result in complementary distension and can be employed to distend collapsed bowel (Chen et al. 1999 Fletcher et al. 2000 Yee et al. 2003). In general, the patient should be rolled such that the collapsed bowel loop is in the most nondependent location (Fig. 14.7). Contraction can appear as a...

Non Tagged Stool

In a minority of cases a small amount of stool remains non-tagged. Fig. 4.8. Patient with right sided sigmoid. There is tagged stool (arrowhead). There is also non-tagged material (arrow). This should be considered a lesion unless the contrary is proved. A correct diagnosis of an 8-mm sessile polyp was made Non-tagged stool < 6 mm is too small too cause any concern as it is generally accepted that polyps < 6 mm do not need to be removed. Hence pseudopol-ypoid lesions < 6 mm caused by...

Inverted Appendiceal Stump and Appendiceal Intussusception

An inverted appendiceal stump can appear identical to a polyp (Fig. 14.13), and is located at the site of prior appendectomy. Both the appendiceal stump and intraluminal neoplasm will enhance with intravenous contrast. Close correlation with the clinical history of incidental inversion-ligation appendectomy may be revealing , but in cases where clinical history is incomplete, endoscopic correlation may be required. Appendiceal intussusception can also occur. Barium enema has the advantage of...

Recommended Technique

It is clear form the above discussion that the practitioner has many options available when attempting to optimise colonic distension prior to scan acquisition. While some techniques have an established evidence-base, others are largely a matter of personal preference. Whatever regime is chosen, it is clear that good distension is absolutely pivotal to the success of any CTC examination. The follow section will provide the reader with details of the authors' preferred methods. Written patient...

Carbon Dioxide

Carbon dioxide (CO2) has been used instead of atmospheric air for insufflation of the colon for colonoscopy as well as for barium enema examination because it has been found to decrease patient discomfort. CO2 is readily resorbed through the colonic wall because of a steep diffusion gradient and it is then exhaled from the lungs. One hundred patients were randomized to undergo colonoscopy with insufflation with either air or CO2. Post-procedural pain was reported in 45 and 31 of patients...

The Right Scanner Parameters to

Andrea Laghi and Pasquale Paolantonio 6.5 Tube Current Setting and Low Dose Protocols 65 6.6 Practical Guidelines 68 Appendix. Glossary of Terms 69 References 70 The advent of CT colonography (CTC) (or, virtual colonoscopy) in 1994 was made possible by the development of spiral CT technology, which provides a volumetric coverage of a cleansed and air-distended colon within a single breath-hold (Vining et al. 1994). The introduction of multidetector row computed tomographic (MDCT) scanners in...

Performance of CAD

Several academic institutions have conducted clinical trials to demonstrate the performance of their CAD systems (Kiss et al. 2002 Nappi et al. 2004b Nappi and Yoshida 2003 Paik et al. 2004 Summers et al. 2001 Yoshida et al. 2002a, b Yoshida and Nappi 2001) that implement the full CAD scheme in the previous section or a part of it. In these studies, optical colonoscopy was used as the gold standard, i.e., the locations of the polyps detected by CAD were compared with the true locations of...

Choice of Rectal Catheter

There is wider scope for using more flexible and thinner catheters during CT colonography compared to barium enema because of the requirement to transmit only gas and because the consequences of anal incontinence are less dramatic. The choice of rectal catheter will mainly depend on local availability, method of insufflation, and individual patient but there is some evidence suggesting that thin tubes are adequate for most circumstances. Perhaps the simplest catheter is a thin plastic or rubber...

Ulcerative Colitis

Colonoscopy Ulcerative Colitis

Ulcerative colitis is an inflammatory bowel disease limited to the mucosa and submucosa of the colon. The disease typically begins in the rectum and continuously extends proximally to involve part of the colon or the entire colon (pancolitis). In 10-40 of cases, the distal ileum is also inflamed, which is referred to as backwash ileitis. The most severe Table 13.2. CTC features of inflammatory bowel disease Discrete irregular wall thickening (continuous vs. discontinuous) Flattening or...

Colorectal Lymphoma

Lymphoma involves the colon either as a primary neoplasm or as a part of a disseminated disease. In contrast to the small bowel, where lymphomas are the most frequent primary, lymphomas in the colon are rare. In secondary colonic lymphoma, the involvement of the gastrointestinal tract follows a previously diagnosed extraabdominal lymphoma (O'Connell and Thompson 1978 Megibow et al. 1983). The primary colonic lymphoma is usually found in middle-aged or elderly people. Males are twice as often...

Automated Insufflation

Automated insufflation devices are now widely utilised across Europe and the US, despite the additional equipment costs. Advocates suggest that insufflating carbon dioxide at controlled flow rates and pressures is convenient for the operator, and improves distension and patient compliance. Early experience comparing a crudely modified laparoscopic insufflator to manual bulb insufflation of room air showed equivocal effects on luminal distension (Ristvedt et al. 2003). More recently, two Fig....

Patient Preparation for CT Colonography

Scopolamine Butylbromide Synthesis

3.3.2 Hyoscine n-Butylbromide 31 References 32 CT colonography or virtual colonoscopy has increasing support as a screening tool for colorectal polyps and carcinoma. This radiologic examination uses the patient data acquired from a helical CT scanner and combines it with computer software that post-processes the data to generate both two- and three-dimensional images of the colon for analysis. However, before the patient undergoes the CT scan, there are initial steps that must be taken to help...

Manual Insufflation

The easiest and cheapest method for distending the colon is to use room air, insufflated via a hand held plastic bulb. Typically patients lie on the CT scanner table in a left lateral position facing away from the operator. A lubricated rectal catheter attached to an insufflator bulb via a connecting tube is then inserted into the rectum and taped to the patient's buttocks. The patient is encouraged to retain any gas and avoid passing flatus by clenching the anal sphincter. Colonic insufflation...

Glucagon

Glucagon is a polypeptide hormone normally produced by the pancreatic islets of Langerhans. It causes an increase in blood glucose, but is perhaps better known for its clinical use as a hypotonic agent for the stomach, small bowel, and colon. Glucagon relaxes the smooth muscle of the gastrointestinal tract and is thought to improve bowel distension and decrease patient discomfort due to spasm. The effectiveness of glucagon is dependent upon location, and it has been found to be most effective...

Surveillance Post Surgery or Post Intervention

With regard to post-surgical conditions in the colon, there is no general agreement about the use of CT colonography. Contrast-enhanced CT colonography has the potential to detect local recurrence, metachro-nous disease, and distant metastases in patients with a history of invasive colorectal cancer (Fletcher et al. 2002 Laghi et al. 2003 Neri et al. 2005). Currently, endoscopy or barium enemas are performed in many cases after colonic surgery for routine surveillance, to detect tumor...

Diagnostic CT Colonography

Patients with positive bowel symptoms, such as change in bowel habits, lower gastrointestinal bleeding, iron deficiency anemia and abdominal pain are eligible to undergo a diagnostic CTC. The patient is scanned in both the supine and prone position, but unlike a screening CTC, the patient is injected with intravenous iodinated contrast material during the supine acquisition (CheN et al. 1999). Injection of contrast aids in the differentiation of polyps versus adherent stool. Studies have also...

Appendiceal Stump Odematous Colonoscopy

Colonoscopy Pathology Images

False positive diagnosis spasm of the Ring of Rossi mimicking tumoral disease a,b supine (a) and prone scanning (b) show persistent incomplete distention of the sigmoid (arrows). Differential diagnosis was made between spasm of the Ring of Rossi and tumoral disease. The soft contours of the lesions suggested a persistent spasm c additional inflation was performed and subsequent re-evaluation showed normal sigmoid. Diagnosis of spasm of the Ring of Rossi was made. Lesson Persistent...

Diverticular Disease

Virtual Colonoscopy Diverticula

Diverticular disease is the most common colonic disease in the Western world, affecting 10-30 of people at age 50 years and 30-60 at age 80 years. However, the disease is asymptomatic in the majority of patients. Together with aging, longstanding low dietary fiber is the main predisposing factor for diverticular disease. Other etiological factors have been suggested, including increased consumption of red meat, fat, and salt. An early stage of the disease is the so-called pre-diverticulosis,...

Diverticulosis

Internal Hemorrhoids Endoscopy

Diverticular disease is exceedingly common, and is seen as focal outpouchings of the colonic lumen projecting beyond the colonic wall on 2D axial and 2D MPR images. Three-dimensional endoluminal images demonstrate the internal orifices projecting from the colonic lumen (Fig. 14.2 and Fig. 14.3). Occasionally, muscular hypertrophy of diverticulosis can cause colonic wall thickening, but in these segments, we usually observe diverticula interposed throughout the regions of colonic wall...

Causes and Solutions to Overcome False Negatives and False Positives

Proneimage

Stefaan Gryspeerdt and Philippe LeferE 8.2 False Negative Diagnosis 87 8.2.1 Failure to Detect the Lesion 88 8.2.1.1 Preparation Related False Negative Diagnosis 88 8.2.1.3 Normal Anatomy and Areas of Danger 89 8.2.1.4 Diverticular Disease 90 8.2.1.6 Small Lesions and Small Flat Lesions 94 8.2.2 Failure to Characterise the Lesions 96 8.2.2.1 Annular Stricturing Lesions 96 8.2.2.3 Small Sessile Polyps 96 8.2.2.5 Pedunculated Lesions 99 8.3 False Positive Diagnosis 99 8.3.1 Preparation Related...

Lesion Size and Colonic Segment Location

The Boston Working Group previously published guidelines on the reporting of colonic lesion features Table 12.1 and the classification of colonic findings for the purposes of suggested follow up Table 12.2 . Some of those parameters will be explained here as they impact the reporting of CTC data. The matching of conventional colonoscopy CC and CTC for size and location is required in order to understand the diagnostic accuracy of the technique. Every effort should be made to measure accurately...

Ileocecal Valve

The ileo-cecal valve is the entry point for small bowel enteric contents as they dump into the cecum. It is important to understand that the ileo-cecal valve is located within a fold within the cecum. The valve should be symmetric with respect to the valve orifice on 2D and 3D views. By narrowing the window and level settings to soft tissue settings, one can visualize the internal fatty attenuation of the valve and its associated fold, and distinguish this from suspicious filling defects Figs....

Pictorial Overview of Normal Anatomy Mimics of Disease and Neoplasia at CT Colonography

14.2 Intrinsic Features of the Normal Colon 176 14.2.4 Collapse and Contraction 178 14.2.6 Inverted Appendiceal Stump and Appendiceal Intussusception 181 14.4 Intracolonic and Extracolonic Processes Mimicking Disease 183 14.4.3 Extrinsic Compression 185 14.5 Colonic Neoplasia at CT Colonography 185 14.6 Conclusion 190 References 192

Crohns Disease

Colon Cancer With Lymph Nodes Affected

Crohn's disease may involve segments of the whole GI tract. However, Crohn's disease most often affects the terminal ileum and the proximal colon. Unlike ulcerative colitis, Crohn's disease typically affects the GI tract in a discontinuous way so-called skip lesions and the inflammatory process is transmural in nature. CT usually misses the early stages of Crohn's disease Biancone et al. 2003 . With progression of the disease, mural thickening and luminal narrowing occur. The outer contour of...

Polyps

Virtual Colonoscopy

Polyps maybe sessile, pedunculated, or flat i.e., with the base measuring more than twice that of the height . Sessile polyps will possess polypoid morphology on axial, 2D multiplanar reformatted, and 3D endoluminal views Fig. 14.23 . When sessile polyps are of sufficient size generally consid- Fig. 14.18a-c. A suspicious filling defect on 2D images a, arrow demonstrates sharp intraluminal projections on 3D endoluminal images b and is not of soft tissue attenuation c . These features indicate...

Relative Contraindications

Pregnancy is a relative contraindication to CTC. The radiation dose and absorbed dose to the fetus during the dual scan is the major issue. In these rare instances that a pregnant patient is suspected to have a colorectal cancer, there is a real risk of perforation with conventional colonoscopy and CTC may be the safer alternative. The gestational age of the fetus is an important factor when contemplating risk. The relative risk of childhood cancers is 1.4 with an exposure of 10 mGy in utero...

Hyoscine nButylbromide

Hyoscine n-butylbromide Buscopan is an anticholinergic agent that has been used as a muscle relaxant for the barium enema examination as well as for CT and MR colonography in Europe. It has not received approval for use in the USA. Buscopan has a different mechanism of action than glucagon and is less expensive. Hypotonia of the colon is induced by its action on the postganglionic parasympathetic receptors in smooth muscle. Contraindications to the use of anticholinergic agents include...