Francis Alenghat, HMS IIIGillian Lieberman, MD

Virtual Colonoscopy in colorectal cancer screening

Francis Alenghat, Harvard Medical School Year IIIGillian Lieberman, MD

Date of RotationNovember 2003

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Patient AA

• 78 year-old female• Iron-deficiency anemia • Scheduled for upper GI endoscopy and

colonoscopy but cancelled due to apprehension

• Episodic rectal bleeding• Agreed to undergo virtual colonoscopy

with conventional colonoscopy follow-up

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Occult or Lower GI Bleeding• Occult:

– Upper GI bleed (varices, gums)– Peptic Ulcers– Angiodysplasia– Benign Polyps– Colorectal Cancer– etc.

• Lower GI Bleed– Colorectal Cancer– Diverticula– Ischemic Bowel – Angiodysplasia– Benign Polyps– Hemorrhoids

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Colorectal Cancer

• 2nd most common cause of cancer-related death in US

• everyone > 50 years should be screened• only <40% of ‘eligible’ persons have been screened• Progress from adenomatous polyps – detection

and resection is curative. 6 mm threshold for malignant potential.

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Screening Options• Fecal occult blood testing – 3 serial samples done at

home and sent away for analysis • Double contrast barium enema • Sigmoidoscopy – half the colon, misses 50% of

neoplasms• Colonoscopy – currently gold standard for screening

with high sensitivity and specificity

• Stool-based molecular screening• Virtual colonoscopy

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Virtual Colonoscopy Basic Technique

1. Bowel prep2. Air insufflation of colon3. Ensure full length insufflation with scout CT4. Supine uninterrupted volume of data through

abdomen – 32 second breath hold. Thin slices ~ 1-2.5 mm.

5. Postprocessing – 3D reconstruction with surface, volume and/or perspective rendering

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Scout CT

After air insufflation After a little more airCourtesy Dr. Morrin

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Virtual Colonoscopy Basic Technique

1. Bowel prep2. Air insufflation of colon3. Ensure full length insufflation with scout CT4. Supine uninterrupted volume of data through

abdomen – 32 second breath hold. Thin slices ~ 1-2.5 mm.

5. Postprocessing – 3D reconstruction with surface, volume and/or perspective rendering

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Axial CT

Polyp

Cecum

SigmoidColon

Courtesy Dr. Morrin

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Axial CT

Polyp

Ascending Colon

Transverse Colon

Descending Colon

Courtesy Dr. Morrin

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Virtual Colonoscopy Basic Technique

1. Bowel prep2. Air insufflation of colon3. Ensure full length insufflation with scout CT4. Supine uninterrupted volume of data through

abdomen – 32 second breath hold. Thin slices ~ 1-2.5 mm.

5. Postprocessing – 3D reconstruction with surface, volume and/or perspective rendering

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Francis Alenghat, HMS IIIGillian Lieberman, MD

3D reconstruction

Polyp

Frontal cutaway

Air-soft tissue interface surface

rendering

Courtesy Dr. Morrin

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Endoluminal Perspective

Polyp

Haustra

Courtesy Dr. Morrin

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Endoluminal Navigation

Courtesy Dr. Morrin

1 2 3 4 5

6 7 8 9 10

Frames from fly-through sequence showing polyp (arrow)

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Follow-up on same-day Optical Colonoscopy

Courtesy Dr. Morrin

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Francis Alenghat, HMS IIIGillian Lieberman, MD

A less subtle diagnosis...

Courtesy Dr. Morrin

3.6 cm polyp

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Francis Alenghat, HMS IIIGillian Lieberman, MD

A less subtle diagnosis...

Courtesy Dr. Morrin

Multiple adenomas

- familial adenomatous polyposis

3.6 cm polyp

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Virtual Colonoscopy pros and cons

• Visualization of entire colon– Explore beyond colonic obstruction and both sides of haustral folds

• Reduced patient discomfort and anxiety– Non-invasive– Fast and does not require sedation

• Lower risk of procedural complications • Sensitivity > 90% (in many studies even better than

conventional colonoscopy)

• Specificity was low (until now), due to residual bowel fluid, fecal residue

• Still requires bowel prep• Not therapeutic• Ionizing Radiation• Cost

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Screening in High Risk Patients

Clearly established as an effective alternative when compared to conventional colonoscopy:

Sensitivity for polyps > 10 mm: 89-92% in studies with > 100 patients. (using same-day conventional colonoscopy as gold standard)

Sensitivity for patients with polyps: 92-100%Specificity for patients with polyps: 72-97% but high prevalence of polyps in this population keeps PPV high

• Personal or family history of Colorectal Cancer

• Current symptoms

• iron-deficiency anemia

• heme positive stool

• hematochezia

• Prior occurrence of polyps

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Francis Alenghat, HMS IIIGillian Lieberman, MD

False Positive• Main culprits are residual fecal material and fluid due

to incomplete bowel prep

• Scanning both supine and prone: – exclusion of shifting material

• IV contrast:– exclusion of non-enhancing material

• Fecal tagging:– exclusion of enhancing material

Techniques to reduce false positives:

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Francis Alenghat, HMS IIIGillian Lieberman, MD

False Positive• Main culprits are residual fecal material and fluid due

to incomplete bowel prep

Stool shift -

not a polyp!

Courtesy Dr. Morrin

supine

prone

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Francis Alenghat, HMS IIIGillian Lieberman, MD

size, size, size

• 50% > 50yrs have polyps - so what’s the screening threshold?

• > 1.0 cm polyps have majority of malignant potential• detection of polyps 5-10 mm may be useful as

clusters of small polyps also have increase potential– sensitivity for these polyps in high risk cohorts: 70-82%

• flat adenomatous lesions also have malignant potential

• thinner slices: 1 - 3 mm• IV contrast: enhance smaller lesions in background of

residual fluid

Techniques to increase sensitivity for small polyps:

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Francis Alenghat, HMS IIIGillian Lieberman, MD

IV Contrast for Increased Sensitivity

IV contrast

Courtesy Dr. Morrin

Submerged polyp seen with contrast on prone scan.

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Screening in Average Risk Patients• 1233 patients in prospective multicenter trial with

same-day conventional colonoscopy as standard– high risk patients excluded– 24 hour bowel prep with phosphosoda, bisacodyl, barium,

diatrizoate meglumine– 1.25 - 2.5 mm collimation, supine and prone– 3D endoluminal display read prior to conventional colonoscopy– stool tagging and digital fluid subtraction

• Sensitivity by patient: 10mm -- 93.8%• Specificity by patient: 10mm -- 96%• Conventional colonoscopy sensitivity:

– 87.5% (prior to unblinding)

Conclusion: VC more sensitive than conventional colonoscopy, with high specificity: threshold of 8mm for f/u therapeutic endoscopy

Pickhardt et al 2003 (NEJM in press) as reported at 4th Intern. Symp. on VC

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Modifications and Frontiers

IV contrast

Fecal tagging

MRI virtual colonoscopy

Computer aided detection

Prepless or minimal prep procedures

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Francis Alenghat, HMS IIIGillian Lieberman, MD

References• Barish MA, Soto J, Ferruci JT. Virtual Colonoscopy: Fourth International Symposium

(Syllabus) Boston 2003.• Dachman AH, Yoshida H. Virtual Colonoscopy: past, present, and future. Radiol Clin

North Am 2003; 41: 377-93.• Fenlon HM, Nunes MB, Schroy PC, Barish MA, Clarke PD, Ferrucci JT. A comparison

of virtual and conventional colonoscopy for the detection of colorectal polyps. N Engl J Med 1999; 341: 1496-1503.

• Ferrucci JT. Virtual Colonoscopy for Colon Cancer Screening: Further reflections on polyps and politics. Am J Roentgenology 2003; 181: 795-7.

• Karlson B-M, Ekbom A, Lindgren PG, Kallskog V, Rastad J. Abdominal US for diagnosis of pancreatic tumor: prospective cohort analysis. Radiology 1999; 213: 107- 11.

• Morrin MM, Raptopoulos V. Contrast-Enhanced CT Colonography. Semin Ultrasound CT MR 2001; 22: 420-424.

• Ransohoff DF, Sandler RS. Screening for Colorectal Cancer. N Engl J Med 2002; 346: 40-44.

• Rosewicz S, Wiedenmann B. Pancreatic carcinoma. Lancet 1997; 349: 483-89.• Walsh JME, Terdiman JP. Colorectal Cancer Screening. JAMA 2003; 289: 1288-1302.

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Francis Alenghat, HMS IIIGillian Lieberman, MD

Acknowledgements

Thank you!!• Martina Morrin, MD

• Larry Barbaras• Gillian Lieberman, MD• Pamela Lepkowski