Does a learning curve exist in endorectal two-dimensional ultrasound accuracy?

Abstract

Dear Sir,We read with interest the paper in Techniques in Colo-proctologybyMorrisetal.[1]whereatwo-dimensional(2D)probe was used in rectal cancer staging. We feel it importantto mention the value of three-dimensional (3D) endosonog-raphy, which we now use routinely in our department.Display of volume data in three perpendicular planesfacilitates the interpretation of ultrasound images andenhances the diagnostic information provided by the data.The comparative accuracy for both techniques is similaraccording to the literature. Tumor invasion prediction hasbeen shown to be 84 and 88 % for 2D and 3D endoson-ography, respectively. In the determination of lymph nodeinvolvement, 3D and 2D endoscopic ultrasound (EUS)provide accuracy rates of 79 and 74 %, respectively [2].However, 3D has obvious advantages. With the use of2D EUS, no direct information is available about the lon-gitudinal extent of the tumor and its spatial relationships.Consequently, a series of transverse images must be inte-grated by the observer to produce a mental impression ofthe real anatomy. This means repeated movements of thescan plane over the region of interest, which can be time-consuming, embarrassing, and painful for the patient. With3D EUS, data from a series of closely spaced 2D imagesare combined to create a 3D volume displayed as a cube.The cube does not remain fixed; it can be freely rotated,rendered, tilted, and sliced to allow the operator to infi-nitely vary the different section parameters and visualizethe lesions at different angles in order to get the mostinformation out of the data.The multiview function also allows up to six differentand specialized views at once with real-time reconstruc-tion. This allows the physician to evaluate arbitrary planesnot available with 2D ultrasound, to improve assessment ofcomplex anatomic situations by 3D display, to measureorgan dimensions and volumes, and to standardize theultrasound examination procedures [3].3D scanning may also allow visualization of obstructingtumors by using reconstructed planes in front of thetransducer, possibly improving therapy planning inadvanced rectal cancer by selecting patients who requireneo-adjuvant therapy.Finally, 3D imaging makes EUS less operator dependentas data can easily be stored on a hard disk allowing a real-time reexamination at a later date without loss of infor-mation, such as in discussion of images at cancer multi-disciplinary team meetings.3D ultrasound facilitates the interpretation of the scanimages and improves the diagnostic confidence in approxi-mately 60 % of the examinations [4].