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Colon Carcinoma


KEY FACTS

Imaging

  • Imaging is critical for detection, diagnosis, staging, and follow-up of colorectal carcinoma (CRC)

  • Detection : CT colonography, plus stool analysis

    • Complementary role with standard colonoscopy

    • Early cancer: Sessile or pedunculated polyp

    • Advanced cancer: "Saddle" or "apple core" lesion

      • –

        Circumferential narrowing of bowel lumen, overhanging borders, mucosal destruction

  • Staging : Helical CT ± MR

    • Short segment (< 10 cm) asymmetric mural thickening & luminal narrowing

    • Pericolonic fat infiltration; spread to adjacent organs

    • Metastases to nodes, peritoneum, liver, ovaries

  • Tumor recurrence and surveillance : PET/CT

    • FDG-avid lesions in chest, abdomen, pelvis

Top Differential Diagnoses

  • Diverticulitis

  • Ischemic colitis

  • Infectious colitis with TB or ameba

  • Ulcerative colitis

  • Endometriosis

Pathology

  • Importance of family history

    • CRC in 1st-degree relatives (↑ risk 2-3x)

    • Familial adenomatous polyposis

      • –

        Accounts for < 1% of all colon cancers)

    • Hereditary nonpolyposis colorectal carcinoma (Lynch syndrome)

      • –

        Accounts for 5% of all colon cancers

Clinical Issues

  • New treatments for metastatic disease (e.g., resection and ablation) offer hope for cure or prolonged survival

    • Demands accurate staging and surveillance for recurrence

Graphic shows an "apple core" constricting tumor of the sigmoid colon with circumferential narrowing of the lumen and a nodular tumor surface, the typical appearance of a left-sided cancer. These patients often complain of constipation and rectal bleeding.

Single-contrast barium enema shows a classic "apple core" lesion
of the sigmoid colon. Note the short segment, irregular, circumferential narrowing of the lumen with destroyed mucosa and nodular "shoulders."

Coronal image in 2D from a CT colonography shows a mass
in the sigmoid due to colon cancer. While this mass was sufficiently large enough to prevent passage of the colonoscope, it was possible to both cleanse and distend the colon proximal to the mass using routine CT colonography methods.

CT 3D endoluminal view in the same patient shows the mass
and its relationship to the remainder of the colon. One of the accepted indications for CT colonography is to screen the colon proximal to an obstructing lesion.

TERMINOLOGY

Abbreviations

  • Colorectal carcinoma (CRC)

Definitions

  • Malignant transformation of colonic mucosa

IMAGING

General Features

  • Best diagnostic clue

    • Short segment colonic wall thickening

  • Location

    • Cecum (10%), ascending colon (15%), transverse colon (15%), descending colon (5%), sigmoid colon (25%), rectosigmoid colon (10%), rectum (20%)

  • Morphology

    • Early cancer: Sessile or pedunculated polyps

    • Advanced cancer: Annular, semiannular, polypoid, or carpet tumors

  • Other general features

    • Radiology is critical for screening, diagnosis, treatment, and follow-up of CRC

    • Screening: CT "virtual colonoscopy" is comparable to colonoscopy for cancer detection by experienced observers

Radiographic Findings

  • On air-contrast barium enema or CT colonography

    • Early cancer: Plaque-like lesion

      • –

        Flat, protruding lesion with little elevation of surface

    • Early cancer: Pedunculated lesion

      • –

        Short and thick polyp stalk

      • –

        Irregular or lobulated head of polyp

    • Advanced cancer: Polypoid lesion (large)

      • –

        Dependent wall: Filling defect in pool of contrast

      • –

        Nondependent wall: Etched in white

    • Advanced cancer: Semiannular "saddle" lesion

      • –

        Transition to annular carcinoma: Polypoid → semiannular → annular

      • –

        Convex barium-etched margins (in profile view)

    • Advanced cancer: Annular "apple core" lesion

      • –

        Circumferential narrowing of bowel lumen, overhanging borders, mucosal destruction

      • –

        High-grade obstruction with ischemia: Thumbprinting of dilated proximal colon

    • Advanced cancer: Carpet lesion

      • –

        Malignant villous tumor may appear as carpet lesion with minimal protrusion into lumen

      • –

        Radiolucent nodules surrounded by barium-filled grooves; finely nodular or reticular pattern

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