Endorectal sonography: laboratory and clinical experience in Bristol.

The normal echographic pattern produced by the colon and rectum has been investigated in vitro. Five basic ultrasonic layers or interfaces have clearly been identified; a first echogenic layer produced by the mucosa, then an echopoor layer representing the mucosa and muscularis mucosae, an echogenic layer which was submucosa, echopoor layer which was muscularis propria and an echogenic layer which was either pararectal fat or serosa. The effectiveness of endoluminal ultrasound (ELU) in the pre-operative staging of rectal cancer has been assessed in a group of 67 patients who were also, where possible, graded by digital examination and in some cases computer aided tomography (CT) (33 patients). Digital examination had an overall accuracy of 50% and could predict invasion beyond or confinement to the rectal with an accuracy of 64%. ELU is a highly accurate method for staging local invasion and when compared to post-operative histopathology had an overall correlation coefficient of 0.88 (p less than 0.001) (Rank Spearman). Our overall accuracy was 91% and it could predict invasion beyond the muscularis propria with a sensitivity of 96%, specificity of 94% and positive predictive value of 98%. In the cohort studied by both radiological techniques ELU was more accurate than CT where overall accuracy was 79%, sensitivity was 84%, specificity was 63% and the positive predictive value was 88%.