Usefulness of endorectal ultrasound after preoperative radiotherapy in rectal cancer

PURPOSE: Our aim was to assess the advantages of endorectal ultrasound after preoperative radiotherapy in rectal cancer, its reliability in tumoral staging, and its capacity to identify completely sterilized lesions. METHODS: From 1994 to 1997, 29 patients with rectal cancer were systematically subjected to endorectal ultrasound before and after preoperative radiotherapy. Each patient was administered 30 to 50 Gy, followed by surgery six to eight weeks after completion of radiotherapy. Endorectal ultrasound was performed using a biplanar (linear and sectorial) endorectal probe. The morphologic, quantitative, and echo-pattern changes of the irradiated tumor were examined. Results of ultrasound findings before and after radiotherapy and a histologic examination of the surgical specimens were compared. Histopathologic studies were used to evaluate macromicroscopical radiation-induced changes, case by case. A comparison between tumoral shrinkage and fibrotic replacement was made using the semiquantitative Dworak's method. RESULTS: Morphologically and quantitatively, postradiation endorectal ultrasound showed the reappearance of anatomic cleavage planes, a considerable shrinkage of the tumor, and in low rectal tumors, an increase in the distance from the anorectal ring in more than 50 percent of the cases. These data had a direct influence on surgical treatment. Histologic examination showed that, in 28 out of 29 cases, fibrosis was the most dominant component of the irradiated lesions, varying by more than 50 to 100 percent of the lesion (four cases pTO). A comparison of postradiation endorectal ultrasound with histopathology revealed that fibrosis became the morphologic basis of ultrasound images; therefore, after radiotherapy, what endorectal ultrasound staged was no longer the tumor but the extent of fibrosis in the rectal wall. A histopathologic examination showed that the residual tumor, when present, was always within the fibrosis, never outside or separate from it. Postradiation endorectal ultrasound showed echo-pattern changes. Some of the changes (more echogenic and non-homogeneous lesions) were histologically related to the persistence of the tumor to a considerable degree; other changes (reappearance of parietal layers) were related to complete sterilization of lesions in two of three cases. CONCLUSIONS: From the morphologic and quantitative point of view, postradiation endorectal ultrasound provides oncologists and surgeons useful information to assess treatment effectiveness and plan the surgical approach. From the tumor staging point of view, our report presents a completely new concept: that six to eight weeks after radiotherapy, endorectal ultrasound no longer stages the tumor, but rather the fibrosis that takes its place. However, postradiation endorectal ultrasound is a valid tool, because the extent of fibrosis in the rectal wall is a direct indication of the depth of residual cancer. A residual tumor, when present, is always inside the fibrosis. Finally, however, as regards the capacity of endorectal ultrasound to exclude or indicate complete sterilization of the lesion, the actual significance of the echo-pattern changes we observed needs to be assessed further by studies on a large number of cases.