Colorectal cancer

Colorectal cancer (CRC) is the most common cancer of the gastrointestinal tract and the second most frequently diagnosed malignancy in adults. CT and MRI are the modalities most frequently used for staging. Surgical resection may be curative although five-year survival rate is 40-50%. 

CRC is common, accounting for 15% of all newly diagnosed cancers, and tends to be a disease of the elderly, with the median age of diagnosis between 60 and 80 years of age 2, slightly younger for rectal cancer. There is also a slight male predilection for rectal cancers, not found in tumors elsewhere in the colon. 

A number of predisposing factors have been identified, including:

Recognized hereditary syndromes are seen in 6% of CRCs. These include:

Clinical presentation is typically insidious:

However initial manifestation may be acute:

Less common presentations include:

  • that of metastatic disease (e.g. respiratory symptoms from lung metastases)
  • paraneoplastic syndromes (e.g. dermatomyositis)
  • bacteremia or bacterial endocarditis with Streptococcus bovis (Streptococcus gallolyticus6

In general:

  • right-sided tumors are larger and present with a mass, distant disease or iron deficiency anemia
  • left-sided tumors present earlier with altered bowel habit

Colorectal cancers, 98% of which are adenocarcinomas, arise in the vast majority of cases from pre-existing colonic adenomas (neoplastic polyps), which progressively undergo a malignant transformation as they accumulate additional mutations 2 (so-called multi-hit hypothesis). 

Morphologically cancers can be:

  • sessile
  • exophytic
  • circumferential (apple core
  • ulcerated 
  • desmoplastic

Rarely the malignant cells will widely invade the submucosa, analogous to linitis plastic of the stomach. These are typically scirrhous adenocarcinomas (signet-ring type).

Metastases may be widespread in advanced disease, although the liver is by far the most common site involved.

Colorectal cancers can be found anywhere from the cecum to the rectum, in the following distribution 2,5:

  • rectosigmoid: 55%
  • cecum and ascending colon: ~20%
    • ileocecal valve: 2%
  • transverse colon: ~10%
  • descending colon: ~5%

Approximately 10% of CRCs have a BRAF mutation, which is more common in females, right colon CRC, advanced stage at diagnosis, and a mucinous histology 7

See: colon cancer staging.

  • sensitivities for polyps >1 cm
  • polyps <1 cm: <50% detection 3

Appearances will reflect macroscopic appearance, with lesions seen as filling defects. These need to be differentiated from residual fecal matter. Typically they appear as exophytic or sessile masses or maybe circumferential (apple core sign). Fistulas to bladder, vagina, or bowel may also be demonstrated.

Rarely the stenotic segment will be long particularly with scirrhous adenocarcinomas.

CT is the modality most used for staging CRC, with an accuracy of only between 45-77% 4, able to assess nodes and metastases.

It is often able to diagnose tumors although it is insensitive to small masses. CT colonography is increasing in popularity as an alternative to colonoscopy.

Most CRCs are of soft tissue density that narrow the bowel lumen 4. Ulceration in larger mass is also seen. Occasionally low-density masses with low-density lymph nodes are seen in mucinous adenocarcinoma, due to the majority of the tumor composed of extracellular mucin. Psammomatous calcifications in mucinous adenocarcinoma can also be present.

Complications may also be evident, e.g. fistulae, obstruction, intussusception, perforation 4.

MRI has a staging accuracy of 73% with a 40% sensitivity for lymph node metastases 1. MRI is having an increasing role to play in the staging of rectal cancer.

Treatment involves local control with resection in almost all cases. Adjuvant chemotherapy is reserved for stage III disease.

Overall 5-year survival rate is 40-50%, with the stage at operation the single most important factor affecting prognosis.

  • Duke A: 80-90%
  • Duke B: 70%
  • Duke C: 33%
  • Duke D: 5%

BRAF-mutated CRC has a poorer prognosis with a median survival of <12 months 7.

Reoccurrence is common:

The tumor marker CEA is routinely used for detecting postoperative early recurrence and metastatic disease (especially liver disease). It is also used for monitoring response to treatment of metastatic disease

  • as with most tumor markers, it is inappropriate for screening given its poor sensitivity and specificity
  • higher levels of CEA are associated with:
    • higher-grade tumors
    • higher-stage disease
    • visceral metastases (especially liver metastases)

Screening recommendations are contentious and vary widely from country to country. An example would be:

  • for persons >50 years of age: an annual fecal occult blood test (often a fecal immunochemical test (FIT)) and sigmoidoscopy/barium enema every 3 to 5 years
  • for first-degree relatives of patients with colon cancer: screening should start at age 40

On CT colonography, the two most useful discriminators of colorectal carcinoma and diverticular disease are absence of diverticula within the structured segment, and shouldered edges, with both features having a high negative and positive predictive value for carcinoma 8. Other features pointing to carcinoma include a shorter segment length, destroyed mucosal folds, straightening of the segment, absence of thickened fascia, and more and larger locoregional nodes.

Other imaging differential considerations on CT include:

Article information

rID: 1153
Synonyms or Alternate Spellings:
  • Colorectal carcinoma
  • Colon carcinoma
  • Colon adenocarcinoma
  • Cancer of the colon
  • Colon tumours
  • Colon tumour
  • Colorectal adenocarcinoma
  • Adenocarcinoma of colon
  • Colon carcinoma
  • Colorectal carcinoma (CRC)
  • Colon cancer
  • Adenocarcinoma of the colon
  • Colorectal carcinomas
  • Colorectal cancers
  • Carcinoma of colon
  • Carcinoma of the colon
  • Carcinomas of the colon

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Cases and figures

  • Figure 1: gross pathology - stenosing adenocarcinoma
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  • Figure 2: gross pathology - with extramural spread
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  • Figure 3: CT/MRI/gross pathology
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  • Case 1: cecal tumor
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  • Case 2: with colovesical fistula
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  • Case 3: with small bowel obstruction
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  • Case 4: mucinous colloid carcinoma of cecum
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  • Case 5: well differentiated adenocarcinoma
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  • Case 6: causing an intussusception
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  • Case 7: cecal cancer
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  • Case 8
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  • Case 9: hepatic flexure with duodenal invasion
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  • Case 10: with ileocoecal intussusception
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  • Case 11
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  • Case 12
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  • Case 13: synchronous colorectal carcinoma
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  • Case 14: with hepatic flexure stricture
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  • Case 15
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  • Case 16: causing small bowel obstruction
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  • Case 17
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  • Case 18: cecal tumor with large pelvic lipoma
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  • Case 19
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  • Case 20: with background FAP
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  • Case 21: with an entero-colic fistula
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  • Case 22: causing large bowel obstruction
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  • Case 23
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  • Case 24: apple core sign
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  • Case 25: stage IV sigmoid colon adenocarcinoma
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  • Case 26: mimic RCC
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  • Case 27
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  • Case 28: ulcerative colitis
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  • Case 29: cecal adenocarcinoma
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  • Case 30: rectosigmoid with hepatic deposit
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  • Case 31: sigmoid adenocarcinoma
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  • Case 32
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  • Case 33: LBO from splenic flexure CRC
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  • Case 34: metastatic cecal adenocarcinoma, polycystic liver and kidney
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  • Case 35: perforated rectosigmoid cancer
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  • Case 36: metastatic sigmoid colon adenocarcinoma
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  • Case 37: on barium study
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  • Case 38: descending colon
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  • Case 39: obstructive
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  • Case 40
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  • Case 41
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  • Case 42
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  • Case 43
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