Diagnosis and staging

The diagnosis of CRC is definitively made at histo-pathologic examination using biopsy or surgical specimens, although radiographic appearances can be pathognomonic. Most often, colonic malignancy is discovered through asymptomatic screening examinations; during endoscopic examinations done for symptoms; as incidental discovery on imaging tests; by clinical examination revealing signs of intes tinal blood loss (hematochezia, ortarrystools); or as a result of abnormal blood tests indicating anemia or elevated carcinoembryonic antigen (CEA). Once discovered or suspected, confirmation and simultaneous staging are the roles most often conferred on CT, MR imaging, ultrasound, CTC, and DCBE. The radiologist must describe tumor size; location; depth of local wall penetration, if feasible; involvement of nodes; spread to other organs; and associated complications, such as obstruction, hemorrhage, abscess formation, inflammation, perforation and the like (within the limitations of the modality). In the following subsections, each modality is reviewed with respect to expected appearances and pitfalls in detecting and staging CRC and its relative accuracy in staging.

Staging of CRC has evolved to the use of tumor, node, metastasis system (Table 3), rather than the Duke's classification or the modified Duke's (As-tler-Collin's) system. These latter systems are not discussed. The tumor, node, metastasis system results in stage groupings for which prognostic and survival statistics are published (Table 4). The stages and associated survival statistics are based on pathologic staging not radiologic assessments (eg, pT1; pathologic T1 not uT1; ultrasound stage T1).

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