Colorectal Cancer: The Radiologists Perspective

1
Colorectal Cancer The Radiologists Perspective
Michael P. Loreto, B.Sc., M.Sc. Nasir Jaffer,
MD University of Toronto Division of Abdominal
Imaging University Health Network and Mount Sinai
Hospital
2
Outline

• Background
• Colorectal cancer incidence and mortality
• Epidemiology
• Pathophysiology
• Role of imaging in
• Screening
• Endoscopy
• CT colonography
• Diagnosis
• Staging
• Treatment

3
Colorectal Cancer (CRC) Incidence and Mortality

• CRC is COMMON
• Third most common malignancy/cause of cancer
  mortality
• Lifetime risk of developing CRC 6
• Lifetime risk of death from CRC 2.6

(Source Statistics Canada)
4
CRC Epidemiology

• Slight male preponderance
• 90 gt50 years of age at time of diagnosis
• Risk factors
• Dietary
• Environmental
• Hereditary

5
CRC Pathophysiology

• Natural history of disease known ? most CRC
  involves progression of ADENOMATOUS polyps to
  carcinoma

1 cm polyp
3 cm carcinoma
(Colonoscopy views)
6
CRC Pathophysiology

• The malignant potential of a polyp is related to
  its size
• Estimated that a 1.0cm polyp takes 10 years to
  develop into invasive cancer

7
Distribution of CRC

• The majority of CRCs occur in the distal colon
• Distal colon (splenic flexure to rectum) 60
• Proximal colon 40

8
Spread of CRC

• Tumour starts in bowel wall mucosa
• Direct extension to surrounding tissues
• Lymphatic spread to regional lymph nodes
• Hematogenous spread to distant organs
• Liver (20-40)
• Lungs (20)
• Adrenal glands, bone, kidneys, pancreas, spleen,
  CNS

9
CRC 5 year Survival Rates

• CRC prognosis is highly dependent upon the stage
  of disease at diagnosis
• Prognosis is good if found early, poor if found
  late
• Localized disease 90
• Regional spread 60
• Distant metastasis 10
• 63 are not found until already metastasized

10
Individual Risk of Developing CRC

• Three categories of patients identified
• Average Risk
• Moderate Risk
• High Risk

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Average Risk Category

• 70-80 of all CRCs
• Age gt 50
• No known risk factors

carcinoma
12
Moderate Risk Category

• 15-20 of all CRCs
• Single adenomatous polyp lt 1 cm
• Single adenomatous polyp gt 1 cm or multiple
  adenomatous polyps of any size
• Personal history of CRC
• CRC in a first degree relative lt 60 years of age
  or CRC in 2 or more first degree relatives

adenoma
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High Risk Category

• 6-10 of all CRCs
• Inflammatory bowel disease (CD and UC)
• Familial Adenomatous Polyposis (FAP)
• Hereditary non polyposis colorectal cancer (HNPCC)

14
CRC Screening Rationale

• Common
• Preventable
• Known precursor lesion
• Goal prevent progression of adenomatous polyps
  to carcinoma
• Curable
• Cancers found at an early stage have much better
  survival rates

15
CRC Screening Methods

• Still generally underutilized
• Current screening methods
• Fecal occult blood testing (FOBT)
• Flexible sigmoidoscopy
• Total colon examination
• Double contrast barium enema (DCBE)
• Conventional colonoscopy
• CT colonography (virtual colonoscopy)

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CRC Screening ACS Recommendations
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Endoscopy

• Endoscopic investigations of the colon
• Sigmoidoscopy
• Colonoscopy
• Performed by gastroenterologists and colorectal
  surgeons

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Sigmoidoscopy

• Technique
• Direct endoscopic visualization of distal colon
  up to the splenic flexure
• Disadvantages
• Misses proximal colon lesions (40 of CRC)
• Misses 10-15 of sigmoid lesions

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Colonoscopy
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Colonoscopy The Gold Standard

• Technique
• Direct endoscopic visualization of the entire
  colon from the rectum to the ileocecal valve
  (ICV)
• Suspicious lesions can be biopsied and removed
• Disadvantages
• Long waiting times (shortage of qualified
  providers)
• Miss rates for adenomas gt 1 cm as high as 6
  (based on repeat colonoscopy)
• Complications
• Bleeding 0.5-2.0
• Perforation 13000 to 15000
• Incomplete exam (unable to get to the ICV)
  10-15

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Double Contrast Barium Enema (DCBE)

• Technique
• Introduction of barium sulfate and air into a
  clean colon via rectal tube under fluoroscopic
  observation
• Performed by radiologists
• Advantages
• Visualization of lumen of entire colon for
  evaluation of intraluminal and mucosal diseases
  such as small ulcers and polyps
• Minimal associated discomfort
• Safe
• Inexpensive and readily available
• Disadvantages
• National Polyp Study (2000) revealed inferior
  detection of clinically significant polyps in
  comparison to colonoscopy

22
DCBE
23
DCBE
adenoma
Sigmoid
Sigmoid
carcinoma
Rectum
24
The National Polyp Study

• Findings of paired colonoscopic and barium
  studies for
• surveillance after polypectomy (moderate risk
  group)

Negative on Barium Enema
Positive on Barium Enema
Polyp Size
lt 0.5 cm
68
32
0.6cm 1.0cm
47
53
gt 1.0cm
48
52
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Failure of DCBE as a Screening Tool for CRC
Reasons and Implications

• Performance of a good air contrast enema is a
  lost art
• Fewer studies being done (affects resident
  training)
• Implications
• Essentially no role for radiologists in CRC
  screening
• Contrast enemas remain a good test for
• assessment of LBO
• localization of colonic disease in pre-operative
  patients
• assessment of the status of a colon anastomosis

26
CT Colonography (CTC) Redefining a Role for
Radiologists in CRC Screening

• First described in 1994
• CT colonography virtual colonoscopy
• Emerging as an accurate, non-invasive test that
  will likely play a future role in CRC screening

27
CTC Procedure

• CT scan of the abdomen after the instillation of
  air into a prepped colon
• Computer rendering of 2D CT images into a 3D
  intraluminal view of the colon in order to look
  for polyps

28
CTC Bowel Preparation

• A major deterrent for patients to undergo colon
  cancer screening
• Required to permit good visualization of the
  bowel mucosa and reduce false-positive reports
  associated with retained feces
• Combination of a low-residue diet and bowel prep
  (eg. Magnesium citrate, Fleet phospho-soda)

29
CTC Colonic Distension (Insufflation)

• Air or CO2 instilled into the colon via rectal
  tube (Foley)
• Air
• Handheld insufflation bulb
• Readily available, cheap
• CO2
• Sourced from a refillable cylinder attached to a
  rectal tube
• Constant gas pressure influx using pressure
  regulated pump
• Intra-colonic pressure and volume of gas
  administered recorded
• IV anti-spasmodics given
• Buscopan (contraindicated in glaucoma)
• Glucagon
• Less abdominal cramping
• More rapid reabsorption post-scanning
• Intra-colonic pressure up to 25mmHg not
  associated with colonic injury/perforation

30
CO2 INSUFFLATORS
Air filter
EZEM CO2 PUMP
LAPAROSCOPIC PUMP (discarded from OR)
31
Image Acquisition

• Helical CT scanning using a multi-detector CT
  scanner
• CT Scout images to assess colonic distension in
  both supine and prone positions
• Rationale redistribution of gas into previously
  collapsed segments, which significantly increases
  the accuracy of polyp detection
• Image acquisition in a single breath-hold to
  decrease motion and respiration artefact

32
CT Scout Images
Supine
Prone
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VALUE OF COMBINED CT (Prone/Supine)
Prone CT
Supine CT
Prone CT shows fluid (lesion obscured)
Supine CT shows the lesion
34
CTC Protocols

• Two types of CT colonography
• Surveillance CTC
• Indications
• Low-risk patients
• Incomplete colonoscopy (low clinical suspicion)
• Prone and supine CT scans without contrast
• Scan from diaphragm to symphysis pubis (incl.
  anus)
• Staging CTC
• Indications
• Colonic lesions (polyps, cancers)
• Incomplete colonoscopy but high clinical
  suspicion
• Prone CT with no contrast
• Scan from top of colon to symphysis pubis
• Supine CT with IV contrast (to stage tumor)
• Scan from above diaphragm to below ischial
  tuberosities (to include liver and anus)

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Image Interpretation

• 600 - 800 CT slices sent to high-end computer
  workstation with special 3D-rendering software

GE Workstation
VITREA Workstation
36
CTC Interpretation Techniques

• 2-Dimensional image rendering (axial, coronal,
  saggital views)
• SPECIAL TECHNIQUES
• Endoluminal 3-Dimensional view (virtual
  colonoscopy)
• Virtual dissection (virtual pathology specimen)
• Tissue Transition Projection (barium enema view)

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Interactive Rendering Modes
Endoluminal
Axial
Saggital
Coronal
38
VIATRONIX V3D Diagnostic Interface

• 3-D Endoluminal view primary mode of viewing
• Has translucency pseudo CAD to facilitate
  polyp identification

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Endoluminal View (virtual colonoscopy)

• V3D diagnostic interface allows virtual
  fly-through of the volume-rendered 3D images
  along an automated center-line path (green line)
• Seamless navigation between the 3D and 2D image
  displays allows rapid 2D correlation of any
  suspected 3D abnormality
• Fly-through in both antegrade and retrograde
  directions to examine hidden surfaces of folds
  and flexures

40
Endoluminal View

• Identification of position w/in the axial length
  of the tubular colonic lumen based on recognition
  of classic anatomic features
• Distal colon ? straight tubular course
• Transverse colon ? triangular folds
• Cecum ? ICV, appendiceal orifice

(Endoluminal view near Cecal pole)
41
Endoluminal View

• Improved depiction of surface morphology over 2D
  views
• 2D images remain important for correlation of
  lesions seen on 3D rendering (improve
  specificity)

42
Advantages of CTC

• Assess lesions
• Accurately localize measure lesion
• Pseudo-lesions better assessed (eg. stool)
• Examine entire abdomen
• Detect other pathologies
• Stage colorectal tumors
• local extension
• distant metastasis

43
Measure and Localize Lesions
Cecal Polyp
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Measuring the Interval Growth of a Polyp
September 2002 sessile polyp 2.2 cm
November 2001 sessile polyp 1.3 cm
45
ENDOLUMINAL VIEW TIP OF THE ICE-BERG OF
COLONIC LESION
Tumor
lumen
AXIAL CT Scan Shows serosal extension of lesion
Endoluminal view Shows intraluminal part of
lesion
(colonoscopy barium enema showed a sub-mucosal
lesion)
46
Problems with CTC Interpretation

• Problems
• 3D pseudo-polyps
• Prominent ileo-cecal valve
• Thick folds
• Retained stool (poor bowel preparation)
• Flat lesions
• Not enough training (few centres performing CTC)

47
Endoluminal View Polyp Detection

• Polyps appear as well-defined round or oval
  intraluminal projections
• Problem retained stool or thick bowel wall
  folds may simulate a polyp (pseudo-polyps)

Tubular adenoma
Retained fecal material
Prominent colonic fold
48
Computer Aided Diagnosis (CAD)

• Special computer software facilitates the
  detection of polyps, helping to differentiate
  polyps from normal colon

Axial CT
Polyp green Fold pink Wall brown
Computer aided
Yoshida H et al Univ of Chicago Radiology
2002222327-336
49
Transluncency Rendering (Pseudo CAD)

• Special technique providing a rapid means for
  assessing the internal composition of polypoid
  lesions

Translucency Code White 1000HU Red 100HU
(polyp) Black -1000HU
(Translucency rendering superimposed on the 3D
endoluminal view)
50
Variations of normal - Thick fold
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CARPET ADENOMAS (Flat lesions)

• Flat lesions are commonly missed by CTC
• Flat polyps tend to have a height lt 2 mm
• 6-36 prevalence rate reported for flat lesions
• Polyps lt 5 mm undetectable with present CTC
  technique

52
CARPET ADENOMAS (Flat lesions)
CT COLONOGRAPHY CORRESPONDING
COLONOSCOPY
Looks like thick fold on CTC ? Flat cancers are
often missed on CTC
53
C.A.D OF LOBULATED CARPET ADENOMA
Transluceny shows polyp with red
54
Virtual Dissection
8 Slice CT (1.25mm /1.0mm)
Rectum
Sigmoid
Transverse
Ileo-cecal valve
POLYP
Ascending colon
(virtual pathology specimen)
55
Tissue Transition Projection (Barium enema
view)

• Not used in interpretation
• Only for lesion localization
• May be useful as a map of lesion location aiding
  subsequent colonoscopy

56
Clinical Indications for CT Colonography

• Incomplete colonoscopy
• Initial surveillance in Low Risk category
  patients
• Elderly patients
• NB NOT for Moderate or High risk patients

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INCOMPLETE COLONOSCOPY

• Due to either obstructing carcinomas or other
  technical factors
• Up to 9 of CRC cases are thought to have
  synchronous malignant lesions
• CT Colonography best done right after colonoscopy
  in order to avoid double bowel preparation
• Useful in clinically suspicious cases or cases of
  known colonic lesions
• Staging CTC protocol completion of colon
  examination staging CT done at one time
• Should not be done after biopsy (risk of
  perforation)

58
INCOMPLETE COLONOSCOPY
Polyp
Polyp
polyp
Obstructing rectal carcinoma Cecal polyp
59
Accuracy of CTC

• Accuracy comparable to conventional colonoscopy
  for detection of clinically significant (gt10 mm)
  polyps
• Average reported sensitivity for large (gt10 mm)
  polyps is 92 and specificity is 97.

60
COMPLICATIONS

• Perforation (due to colonic distension)
• Radiation exposure
• Contrast reaction (staging CT only)

61
Bowel Perforation

• Uncommon
• Usually post-biopsy
• SOLUTION
• Pressure regulated insufflation of colon

62
RADIATION DOSE IN CT COLONOGRAPHY
CTC Staging1 IV contrast
6.0
6.0
CTC Screening1 No IV contrast
EFFECTIVE DOSE (mSv)
3.0
3.0
CXR
0.1
0
X-ray Exams
1 Data calculated from two MSH cases
63
Fecal Tagging and Electronic Cleansing

• Development of fecal tagging agents to avoid full
  bowel catharsis (a major deterrent to colon
  screening investigations), but also useful in
  prepared colon for removal of residual fluid and
  retained fecal matter
• Patients drink barium and water soluble contrast
  ? tagging of residual fluid and debris with oral
  contrast material
• Digital removal of the opacified fluid
  ("electronic cleansing") by simple thresholding

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Fecal Tagging and Electronic Cleansing

• Advantages
• Digital removal of opacified residual fluid
  allows 3D evaluation of colonic mucosa that would
  have otherwise been obscured
• Barium tagging of adherent stool increases the
  specificity for true polyps on CT colonography
• Problems
• Suboptimal tagging ? creation of artefacts
  (pseudo-polyps)
• Over-thresholding ? removal of true polyps

65
Fecal Tagging and Electronic Cleansing
Before
After
Images courtesy of Viatronix
Images courtesy of Viatronix
66
Role of Imaging in CRC Diagnosis

• CRC is a pathological diagnosis
• CTC may allow patients to obtain reliable
  information about the status of their colonic
  mucosa non-invasively and then proceed to
  conventional colonoscopy for polypectomy
• Pathology specimens can be acquired from
  colonoscopy (polypectomy/biopsy) or surgical
  resections

67
Role of Imaging in CRC Staging

• CT
• Abdomen/Pelvis for local staging and assessment
  of liver for metastases
• Thorax for distant spread to lungs
• U/S
• Transrectal U/S used for local staging of rectal
  cancer
• Assessment of liver for metastases

CT
U/S
68
Role of Imaging in CRC Treatment

• Treatment dependent upon stage treatment for
  cure vs. palliation (symptom relief)
• Imaging provides detailed information required
  for
• Surgical resection of
• primary tumour
• liver segments containing isolated metastases
• Percutaneous image-guided ablative therapies for
  non-resectable liver mets (interventional
  radiology)
• CT or U/S-guided
• RFA, EtOH
• Chemo-embolization

69
Summary

• CRC is common and a leading cause of cancer
  mortality worldwide
• The pathophysiology of CRC is well defined with
  progression of adenomatous polyps to carcinoma
• Imaging plays a role in the screening, diagnosis,
  staging and treatment of CRC
• Although colonoscopy remains the gold standard
  for CRC screening it has limitations
• CT colonography is emerging as an accurate means
  of assessing the colon for polyps and holds
  promise as a non-invasive means of CRC screening
• Diagnosis of CRC is a pathological one
• CT is the mainstay of CRC staging with distant
  spread most commonly to the liver and lungs
• Imaging plays a role in directing targeted
  therapeutic interventions such as surgery or
  ablation

70
References
Canadian Cancer Statistics 2004, Canadian Cancer
Society (www.cancer.ca) Cancer Facts and
Figures, ACS 2000, American Cancer Society
(www.cancer.org) Winawer SJ et al A comparison
of colonoscopy and double contrast enema for
surveillance after polypectomy. NEJM 2000
342(24)1766-1772 Fenlon et al Occlusive
carcinoma Virtual Colonoscopy in preoperative
examination of proximal colon . Radiology
1999210423-428 OHare A and Fenlon H Virtual
colonoscopy in the detection of colonic polyps
and neoplasms. Best Practice and Research
Clinical Gastroenterology 2006
20(1)79-92 Ferrucci JT Colon Cancer Screening
with Virtual Colonoscopy Promise, Polyps,
Politics. AJR 2001 177 975-988 www.auntminnie.c
om (Radiology website) Pickhardt PJ Electronic
Cleansing and Stool Tagging in CT Colonography
Advantages and Pitfalls with Primary Three
Dimensional Evaluation. American Journal of
Roentgenology 2003 181(2)799-805