Preoperative staging of rectal cancer using a 7.5 MHz front-loading US probe

Background: Conventional echoendoscopes have disadvantages when used for st aging colorectal cancer including the inability to pass the instrument thro ugh tight stenosis and limited maneuverability. This study evaluated the pr eoperative use of a newly developed 7.5 MHz front-loading ultrasound probe (FLUP) for local staging of rectal cancer. Methods: A 7.5 MHz FLUP diameter 7.3 mm, was used in this study. The mechan ical shaft portion of the probe can be passed in retrograde fashion through the accessory channel of a standard colonoscope. Thirty-nine patients with rectal cancer underwent ultrasonography with this probe. The tumors were s taged using the TNM system, and the results were compared with the histolog ic findings of the resected specimens, Results: The FLUP proved to be satisfactory, with respect to maneuverabilit y, for traversing stenosis and accurate recognition of small tumors under d irect endoscopic control. The accuracy of the FLUP for T staging was 82% (3 2 of 39) for all tumors, 90% in pT1, and 79% in pT2 to pT4 tumors. The accu racy of the FLUP for N staging was 72% (23 of 32) overall. The sensitivity was 83%, the specificity was 65%, the positive predictive value was 59%, an d the negative predictive value was 87%. Conclusions: The 7.5 MHz FLUP appears to be useful for preoperative local s taging of rectal cancer. This system makes it technically easier to image s mall cancers as well as advanced rectal cancers.