‘surface map’ of appendix – a novel tool for pre-operative demonstration of appendicular location with reference to mcburney’s point using multi-detector ct.

Abstract

According to conventional teaching in surgical practice, McBurney's point is the anatomical landmark for locating the appendix and is commonly described as the junction of the lateral and middle thirds of the line joining the right anterior superior iliac spine and the umbilicus (1). Several studies have, however, suggested a significant discrepancy between the McBurney's point and the exact anatomical location of the appendix (2, 3). Multidetector computed tomography (MDCT) is a "one-stop" imaging solution for effective diagnosis of acute appendicitis, with a sensitivity and specificity ranging from 87%−100% and 89%−99%, respectively (4). Similar to the way surgeons use McBurney's point to decide the site of an open appendicectomy incision, the MDCT "surface map" provides a representation of the appendicular base over the anterior abdominal wall in a single image.The present study evaluated the role of MDCT "surface mapping" of the appendix in demonstrating the variation in the location of the appendicular base with reference to McBurney's point and also to anticipate the surgical implications of these results in patients with acute appendicitis. Materials and methodsThis prospective study included a total of 74 patients who had MDCT (Somatom Sensation Cardiac 64 CT scanner, Siemens AG Healthcare, Erlangen, Germany) of the abdomen for varied clinical indications over a period of two months. Patients with a clinical history of any abdominal surgery, systemic malignancy, radiotherapy, or tuberculosis were excluded. A contrast-enhanced CT study of the abdomen was performed in venous phase with a data acquisition time of 6.15 s, scan delay of 60 s, beam collimation of 0.6 mm, gantry rotation time of 0.5 s, and pitch of 1.15. The peak tube voltage range was 100−120 kV, and the current range was 180-225 mAs, using the "care-dose" technique. The images were reconstructed at 3 mm thicknesses in the axial, sagittal, and coronal planes. Because the study did not affect the routine filming and reporting pattern, no ethical approval was required. Post-processing of the MDCT data was performed using the INSPACE software (Siemens AG Healthcare) and a "surface map" was reconstructed with a superimposed measurement grid. The software utilized the volume rendering technique (VRT) of MDCT. A detailed step-wise algorithm with explanatory images is shown in Fig. 1. An illustrative MDCT "surface map" is shown in Fig. 2. The "zero" of the measurement grid corresponded to the umbilicus on the "surface map" image. Post-processing was performed by a single CT technologist, under the direct supervision of the radiologist. The variations in the location of the appendicular base with reference to McBurney's point were tabulated along the cranio-caudal and medio-lateral axes. The location of the appendicular base along MATERIALS AND METHODSThis prospective study included a total of 74 patients who underwent an MDCT study of the abdomen for various clinical indications. Post-processing of the data was performed and a "surface map" of the a...