Pitfalls of Using Three-Dimensional CT Colonography with Two-Dimensional Imaging Correlation

137 T colonography is an imaging technique that enables both two-dimensional (2D) and three-dimensional (3D) evaluation of the colon [1–3]. Although debate continues regarding which rendering technique should be used for primary evaluation, the techniques (2D and 3D) are complementary, each increasing the value of CT for colonic lumen evaluation. Two-dimensional CT colonography, when used as the primary imaging technique, may be advantageous in that data may be evaluated in a more time-efficient fashion [2, 3]. When a potential filling defect is identified on 2D CT colonography, 3D imaging is used to determine whether its morphology is linear (interhaustral fold) or polypoid (stool or polyp) [2, 3]. Three-dimensional CT colonography has the potential to visualize smaller lesions than 2D CT colonography [4]. Although some additional small lesions may be identified, evaluating CT colonography data entirely with 3D imaging is time-consuming. Moreover, often lesions are detected using 3D CT colonography that show morphology consistent with a polyp or neoplasm. When these same areas are investigated with 2D CT colonography, a variety of normal structures may be found to represent these morphologic abnormalities. Whether one uses 2D or 3D as the primary rendering method, the pitfalls on 3D imaging need to be recognized. Three-dimensional morphologic abnormalities can be divided into processes that are intrinsic or extrinsic to the colon. Our purpose is to describe the normal colon with 3D CT colonography and to show how 2D imaging can be used to establish the cause of an abnormality depicted with 3D rendering.