Colorectal adenocarcinoma is the most common colorectal malignancy originating from glandular epithelium of the colon and rectal mucosa. It is the 3rd most common cancer worldwide and the 2nd leading cause of cancer-related death. It accounts for over 95% of cases. The adenoma-carcinoma sequence is well-established with sequential accumulation of APC, KRAS, and TP53 mutations. Distant metastases are present in 20% of cases at diagnosis. CT colonography and contrast-enhanced CT are the primary imaging modalities for staging.
Age Range
40-85
Peak Age
65
Gender
Male predominant
Prevalence
Common
Colorectal adenocarcinoma follows the classic adenoma-carcinoma sequence: normal mucosa → aberrant crypt focus → adenoma → dysplasia → invasive carcinoma. This process takes an average of 10-15 years and begins with APC tumor suppressor inactivation (chromosome 5q loss), followed by KRAS oncogene activation, 18q loss (SMAD4/DCC), and finally TP53 inactivation. The tumor infiltrates the bowel wall transmurally — progressing from mucosa to serosa and potentially invading pericolic fat and adjacent organs. The annular growth pattern narrows the lumen creating the classic 'apple-core' appearance — the most diagnostic finding on CT and barium studies. Tumor neovascularization is irregular and leaky (VEGF-dependent) — heterogeneous enhancement and pericolic vascular congestion on contrast-enhanced CT reflect this neoangiogenesis. Lymphatic spread occurs sequentially to pericolic, mesocolic, and para-aortic lymph nodes. Hematogenous spread most commonly goes to the liver (via portal vein), then lungs.
Annular luminal narrowing with shouldered margins — resulting from the tumor circumferentially encasing the bowel wall and narrowing the lumen. It is the most diagnostic finding on CT colonography and contrast-enhanced CT. Proximal dilation may accompany. This appearance is the signature finding of colorectal adenocarcinoma and suggests malignancy with high specificity.
Annular luminal narrowing with shouldered margins — classic apple-core appearance. The tumor circumferentially encases the bowel wall, narrowing the lumen. Proximal dilation and fecal stasis may accompany.
Report Sentence
An annular wall thickening and luminal narrowing measuring approximately ___ cm in length is seen in the ___ segment with shouldered margins creating an apple-core appearance; colorectal adenocarcinoma should be the primary consideration.
Focal asymmetric wall thickening (>5 mm, usually >10 mm) with soft tissue mass. Thickening may be eccentric or polypoid. Solid component showing heterogeneous enhancement may contain necrotic hypodense areas.
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Asymmetric wall thickening measuring approximately ___ mm with a heterogeneously enhancing soft tissue mass is seen in the ___ segment.
Pericolic fat stranding — indicating tumor invasion through serosa into pericolic fat (T3 stage). Pericolic vascular congestion (comb sign-like) may accompany.
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Pericolic fat stranding is seen adjacent to the tumor, suggesting serosal penetration (T3 stage).
Enlarged pericolic, mesocolic, or para-aortic lymph nodes (short axis >10 mm). Round morphology, central necrosis, or heterogeneous enhancement suggest pathologic lymph node.
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Pathologic lymphadenopathy with short axis measuring up to ___ mm is seen in the pericolic/mesocolic region adjacent to the tumor.
Hypodense lesions in the liver — may show peripheral rim enhancement (target sign) in portal venous phase. Colorectal metastases most commonly spread to the liver (70-80% of hematogenous metastases).
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Hypodense lesions showing peripheral rim enhancement are seen in multiple liver segments, consistent with metastatic disease.
Marked diffusion restriction on DWI (high signal) with low signal on ADC map. Reflects tumor cellularity and malignancy grade. Particularly valuable in rectal carcinoma staging.
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Marked diffusion restriction is seen in the rectal/colonic wall thickening, consistent with a highly cellular malignant process.
Intermediate to high signal mass on T2W. Tumor is easily distinguished from normal bowel wall. Relationship to mesorectal fascia (CRM — circumferential resection margin) is a critical staging finding in rectal cancer.
Report Sentence
An intermediate signal mass is seen in the rectal lumen on T2W with a distance of ___ mm to the mesorectal fascia.
Marked hypermetabolic uptake on FDG-PET (SUVmax usually >5). High sensitivity for detection of primary tumor, regional, and distant metastases. Valuable for treatment response assessment.
Report Sentence
A hypermetabolic colon/rectal mass with SUVmax of ___ is seen in the ___ segment.
Criteria
Most common subtype (85-90%). Shows glandular differentiation. May be well, moderately, or poorly differentiated.
Distinct Features
Classic apple-core or polypoid mass appearance on CT. High FDG-PET uptake. Responds to standard chemotherapy regimens (FOLFOX, FOLFIRI).
Criteria
More than 50% of tumor contains extracellular mucin. Accounts for 10-15% of cases. May be associated with MSI-H.
Distinct Features
Low-density (mucinous) mass on CT — mucin appears hypodense as it is near water density. May be false negative on PET-CT (low cell density). Poor prognosis. Increased risk of peritoneal carcinomatosis.
Criteria
More than 50% of tumor cells show signet ring morphology (intracellular mucin displaces nucleus peripherally). Less than 1% of cases. Most aggressive subtype.
Distinct Features
Diffuse infiltrative growth (linitis plastica-like). Frequent peritoneal carcinomatosis. May present at young age. Very poor prognosis.
Criteria
Solid growth pattern, prominent lymphocytic infiltration. Strong association with MSI-H. Good prognosis despite poorly differentiated appearance.
Distinct Features
Frequently right colon location. Candidate for immunotherapy (pembrolizumab). May appear as large, well-circumscribed mass on CT.
Distinguishing Feature
Lymphoma usually shows longer segment involvement, homogeneous wall thickening, non-obstructive (aneurysmal dilation), and more widespread lymphadenopathy. Adenocarcinoma is characterized by obstructive apple-core appearance.
Distinguishing Feature
Diverticulitis shows symmetric/concentric wall thickening, pericolic inflammatory changes, and diverticula. Adenocarcinoma shows asymmetric, focal thickening with luminal narrowing and shouldered margins. Lymphadenopathy in diverticulitis is usually reactive.
Distinguishing Feature
Crohn disease shows skip lesions, mesenteric-sided wall thickening (asymmetric), fistulae/sinus tracts, and comb sign. Adenocarcinoma is characterized by focal mass/annular narrowing without skip lesions. Clinical history and colonoscopy are differentiating.
Distinguishing Feature
Villous adenoma appears as polypoid, fragile mucosal-surfaced, mucin-secreting mass. Bowel wall is intact (no invasion). Adenocarcinoma shows transmural invasion, pericolic fat stranding, and lymphadenopathy.
Distinguishing Feature
GIST appears as a well-defined, submucosal, exophytic mass that does not narrow the lumen with usually intact mucosal surface. Adenocarcinoma is mucosal in origin, lumen-narrowing, with shouldered margins.
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
3-monthSurgical resection is the cornerstone of colorectal adenocarcinoma treatment. Colonoscopic biopsy confirms diagnosis. TNM staging (AJCC 8th edition) guides treatment plan. Stage I-III undergoes curative surgery (colectomy + mesocolic excision), total mesorectal excision (TME) for rectal cancer. Stage II-III receives adjuvant chemotherapy (FOLFOX); neoadjuvant chemoradiation (nCRT) is standard for rectal cancer. Stage IV treatment depends on RAS/BRAF mutation and MSI status for targeted therapy selection (cetuximab, bevacizumab, pembrolizumab). Postoperative follow-up: CEA + CT every 3 months, colonoscopy at year 1, then every 3 years. 5-year survival is 90% for stage I and 15% for stage IV.
Most common GI malignancy. Surgery is curative in early stages. TNM staging determines treatment plan. Liver metastasis is the most common site of distant spread.