Diagnostic Ultrasound - Abdomen and Pelvis

Large Bowel Malignancy
TERMINOLOGY
Synonyms
• Colorectal, colon(ic), or rectal cancer, neoplasia, malignancy
Definitions
• Malignant lesion of colon or rectum
IMAGING
General Features
• Best diagnostic clue
○ Focal segmental thickening or mass lesion of
colon/rectum
• Location
○ Ascending colon: 30%
○ Sigmoid colon: 25%
○ Rectum: 20%
○ Descending colon: 15%
○ Transverse colon: 10%
• Morphology
○ Circumferential, annular, "apple core," semiannular,
eccentric, sessile, pedunculated, exophytic, desmoplastic
Ultrasonographic Findings
• Normal colonic wall seen on US as 5 distinct alternating
hyperechoic and hypoechoic layers: Gut signature
• Colon cancer is seen on US as
○ Irregular hypoechoic lesion causing abrupt, segmental
loss of normal wall stratification
○ Irregular wall thickening that may be eccentric or
circumferential affecting short segment
○ Hyperechoic foci representing intraluminal gas or feces
may be seen within hypoechoic mass (pseudokidney
appearance)
○ Dilatation of prestenotic segment
○ Disappearance of colonic haustra
○ Increased vascularity may be seen with Color Doppler
• Staging of colon cancer with US
○ Tis: Focal hypoechoic lesion in contact with mucosa or
deep mucosa
○ T1: Focal hypoechoic lesion infiltrating submucosa, but
without involvement of muscularis propria (MP)
○ T2: Focal hypoechoic lesion infiltrating MP
○ T3: Focal hypoechoic lesion penetrating MP but not
involving adjacent organs
○ T4: Focal hypoechoic lesion penetrating serosal surface
• Perifocal or regional hypoechoic lymph nodes with loss of
normal nodal architecture
Radiographic Findings
• Double-contrast barium enema
○ Annular: Focal circumferential luminal narrowing with
irregular margins and acute shouldering (apple core)
○ Semiannular: Eccentric luminal narrowing with irregular
margins
○ Intraluminal: Flat lesion with broad base (sessile) or lesion
with stalk (pedunculated) protruding into lumen
○ Exophytic: Focal defect or "puckering" indicating base of
lesion
○ Desmoplastic: Luminal distortion, tethering, and
angulated margins of lumen
CT Findings
• CECT
○ Intraluminal: Early cancers or cancerous polyps seen as
intraluminal lesions
○ Mural: Focal asymmetric, irregular, or circumferential
thickening of colonic wall
○ Extramural
– Perilesional fat stranding
– Nodular or broad-based extramural tissue extension
into pericolonic fat
– Expansion of draining veins by tumor indicative of
extramural venous invasion
– Infiltration of adjacent organs
○ Metastatic deposits: Typically to liver, lung, and bone
○ Nodal deposits
• CT colonography
○ Small polyps or lesions appear as intraluminal filling
defects
○ Mural and extramural changes overlap with CECT
findings
MR Findings
• Typically used for local staging of rectal cancer
○ Useful for T staging and relationship to circumferential
resection margin (CRM)
– Relationship to CRM dictates management and need
for adjuvant chemoradiotherapy
• Mesorectal and pelvic side wall nodal metastases
○ Loss of round morphology
○ Loss of homogenous signal
○ Demonstrate restricted diffusion
• Extramural venous invasion
○ Intermediate signal tumor extends into and expands
adjacent veins
Imaging Recommendations
• Best imaging tool
○ MR for local staging of rectal cancer
○ CT for local staging of colon cancer
○ CT and PET/CT for evaluation of metastatic disease
○ US not routinely used for diagnosis or staging; cancer
may be detected incidentally on routine US examination
for evaluation of abdominal pain
– Endoanal US has role in T staging of rectal cancer
DIFFERENTIAL DIAGNOSIS
Diverticulitis
• Background diverticulosis
• Wall thickening, adjacent inflammatory changes, and
reactive lymph nodes can mimic colonic cancer
• Longer segment of thickening (> 10 cm)
Inflammatory Bowel Disease (IBD)
• Bowel wall thickening is more symmetrical and may affect
longer segment
• Involvement of terminal ileum favors Crohn disease
• Increase in fatty submucosal layer with preservation of gut
signature
• Penetrating ulcers seen in IBD may breach serosa, but is
more focal, less broad based, and not seen in association
with hypoechoic mass
Diagnoses: Bowel
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