Complications of CT colonography: A Review

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Abstract

Since its inception, one of the main advantages of computed tomography colonography (CTC) over colonoscopy has been its assumed superior safety profile. However CTC is not without complication and adverse events are well described. Although the risks of insufflation, bowel preparation, contrast media and radiation dose are very small, they are not insignificant. This review discusses the potential hazards and complications associated with the technique, and discuss precautions, which may lessen the risk of occurrence.

Introduction

Computed tomography colonography (CTC) is increasingly disseminated as the leading radiological technique for examination of the whole colon. Whilst in Europe its role is currently mainly in the investigation of symptomatic patients, elsewhere it is strongly advocated for colorectal cancer screening. Meta-analysis data suggests CTC is effective in detecting significant colonic neoplasia, notably cancer and large polyps ≥1 cm [1]. Since its inception, one of the main advantages of CTC over colonoscopy has been its superior safety profile. Advocates of CTC point to its less invasive nature and lower risks of perforation, bleeding and cardiac problems. However CTC is not without complication and adverse events are well described. This review discusses the potential hazards and complications associated with the technique, and discusses precautions, which may lessen the risk of occurrence.

Section snippets

Colonic perforation

Colonic perforation may occur after any procedure involving instrumentation or gas insufflation of the large bowel. This includes established procedures such as endoscopic flexible sigmoidoscopy, colonoscopy and double-contrast barium enema examination. Perforation following CTC is also well described.

The aetiology of perforation may be direct trauma to the bowel wall in the case of endoscopy, or rupture following gaseous distension of the bowel. The reported perforation rates for colonoscopy

Causes of Perforation following CT Colonography

The limited number of cases of perforation following CTC reported in the literature together with the variations in insufflation technique and patient cohorts makes it difficult to find factors which are statistically associated with an increased risk of colonic perforation. The three large reports of CTC experience describe 18 cases of perforation in 50, 000 CTC examinations. Evaluation of the possible causes was possible in 13/18 (72%) of the perforations described (Table 2). In some cases

Cardiovascular effects of CT colonography

Unlike endoscopy, intravenous analgesia and sedation are not used prior to CTC. Furthermore colonic manipulation with associated vagal stimulation is theoretically less during CTC than colonoscopy. There are thus good reasons why the cardiovascular stresses of CTC may be less than colonoscopy.

A comparative study evaluating the cardiovascular effects of CTC and endoscopy was performed in 2003 [24]. A total of 144 patients with rectal bleeding or suspected colonic neoplasia underwent CTC followed

Use of spasmolytic agents

Spasmolytic agents are often used during CTC in order to reduce peristalsis and therefore improve image quality. Common spasmolytic agents include hyoscine butylbromide (Buscopan) and glucagon. Buscopan is an anticholinergic agent, which relaxes colonic smooth muscle via its effect on the parasympathetic ganglia. Intravenous administration of 20 mg Buscopan prior to CTC has been shown in a prospective study of 145 patients to significantly improve colonic distension [32]. It also has the added

Bowel preparation

A discussion of the options for preparing the bowel prior to CTC is beyond the remit of this review. However full purgative bowel-preparation is often frequently used prior to CTC [14].

Bowel purgation risks dehydration, electrolyte disturbance and may potentiate renal impairment. Oral sodium phosphate (OSP) products were a popular choice to prepare the bowel prior to CTC [34], with a double-dose (90 ml) used in a landmark clinical trial of screening CTC [35]. In May 2006 however, the US Food and

Contrast media

The use of intravenous contrast media (CM) is usually recommended for symptomatic patients undergoing CTC [14]. The risks of iodinated contrast media relate to both anaphylactoid acute adverse reactions and also to contrast-induced nephropathy.

Acute severe or fatal reactions to contrast media are unrelated to dose and often unpredictable. The reactions have features of anaphylaxis (skin reactions, hypotension, angioedema and airway obstruction) but are usually IgE negative [46]. The incidence

Infection risk

The effect of colonic distension on the translocation of gut flora has been described in patients undergoing colonoscopy [50], [51]. It has been proposed that instrumentation and disruption of mucosa allows endogenous microbial flora in the gut to translocate, leading to systemic bacteraemia.

The rate of bacteraemia associated with colonoscopy range from 0% to 25% with a mean frequency of 4.4% [52]. Although cases of septicaemia [53], [54], [55], [56] and infective endocarditis [57], [58], [59],

Radiation dose

The biological effects of radiation exposure can be divided into those ‘deterministic’ effects which are seen only above a given threshold dose, and ‘stochastic’ effects which occur with increasing probability as dose increases, but with no lower dose threshold. Deterministic effects are not seen with dose range used for diagnostic radiology, and therefore for CT colonography only the potentially carcinogenic stochastic effects from low-dose exposure are of concern.

The best data available on

Conclusions

The literature suggests CT colonography is safer than colonoscopy, but not immune from complications. The risks of insufflation, bowel preparation, contrast media and radiation dose are small but not insignificant. It is always important to give consideration to techniques to reduce risk.

Acknowledgements

This work was undertaken at the Comprehensive Biomedical Centre, University College Hospital London, which received a proportion of the funding from the National Institute for Health Research. The views expressed in this publication are those of the authors and not necessarily those of the UK Department of Health.

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