CASE 7491 Published on 27.04.2009

CT colonography: pedunculated polyp and technical remarks.

Section

Abdominal imaging

Case Type

Clinical Cases

Authors

Angeli S, Cini L, Neri E, Faggioni L, Caramella D, Bartolozzi C.

Patient

64 years, male

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Clinical History

A 64 year-old man underwent CT colonography following incomplete optical colonoscopy for colorectal cancer screening purposes.

Imaging Findings

The patient underwent CT colonography (CTC) as diagnostic completion after an incomplete optical colonoscopy due to patient’s intolerance. The CTC acquisition was carried out in the supine and prone position using a low radiation dose protocol. Patient preparation for CTC consisted of residue-free diet starting three days before CTC, together with assumption of a mild laxative (polyethilenglycole, PEG) for colon cleaning purposes. Faecal tagging was also performed in order to improve diagnostic accuracy through oral administration of 50mL 370-mgI/mL iodinated contrast material three hours before CTC. Colonic distension was obtained by insufflating 3.5L of carbon dioxide through an automatic insufflator, together with administration of an antispasmodic agent (N-butylhyoscine bromide) in order to maximize colonic distension and improve patient comfort. CTC images obtained in the supine position showed a polyp in the descending colon that abuts in the colonic lumen, though it is not well characterized on 2D images or on virtual endoscopy views, as it is almost totally covered by the fluid remnant. On the other hand, the polyp can be well recognized on the images obtained in the prone position, and is characterized as a 13-mm mucosal pedunculated lesion. The above finding was further evaluated by means of virtual endoscopy and virtual dissection views of the colon. The remaining colonic segments were free from parietal lesions. Optic colonoscopy was subsequently performed that confirmed presence of the polyp. This latter was excised and was histologically characterized as a tubulo-villous adenoma with low grade dysplasia.

Discussion

Colorectal cancer is the second most commonly diagnosed cancer in men and the third in women. In the United States it is the second cause of cancer-related death representing about 10% of neoplastic deaths in both men and women, with an incidence of about 150,000 new cases and 50,000 deaths per year. It is widely accepted that the adenoma-carcinoma sequence represents the process by which most colorectal cancers arise, and evidence supporting this hypothesis has increased rapidly in recent years. Identification of adenomatous polyps is the primary goal of screening programs and is aimed at stopping the adenoma-carcinoma sequence. CTC is a recently developed imaging modality allowing the evaluation of the entire colon, and since March 2008 it has been recognized as a recommended test for colorectal cancer screening by the American Cancer Society; in particular, CTC is indicated as a second-level diagnostic modality in case of incomplete optic colonoscopy. Optimal patient preparation and image acquisition protocol are crucial as to maximize the diagnostic yield of the examination. The rationale for data acquisition in both the supine and prone position is to achieve adequate air distension and gravitational distribution of fluid and stool remnants in the various colonic segments. Post-processing is also essential for systematic analysis of CTC datasets in both positions, contributing to increase overall diagnostic performance.

Differential Diagnosis List

Pedunculated polyp of the descending colon.

Final Diagnosis

Pedunculated polyp of the descending colon.

References

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Case information

URL:	https://www.eurorad.org/case/7491
DOI:	10.1594/EURORAD/CASE.7491
ISSN:	1563-4086

Figure 1

CTC in supine position.

Polyp (arrow) abutting in the colonic lumen, as shown on axial CTC image acquired in the supine position. Local bowel distension is suboptimal; a layer of intraluminal iodinated contrast material is adjacent to the lesion.

Virtual endoscopy view of CTC dataset acquired in the supine position. The presence of profuse fluid remnant prevents adequate visualization of the polyp.

Figure 2

CTC in prone position.

Axial CTC image acquired in the prone position. Pedunculated polyp can be seen more clearly than in the supine acquisition, partly due to much better colonic distension.