Usefulness of endorectal ultrasound after preoperative radiotherapy in rectal cancer - Comparison between sonographic and histopathologic changes

PURPOSE: Our aim was to assess the advantages of endorectal ultrasound afte r preoperative radiotherapy in rectal cancer, its reliability in tumoral st aging, and its capacity to identify completely sterilized lesions. METHODS: From 1994 to 1997, 29 patients with rectal cancer were systematically subj ected 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 performe d using a biplanar (linear and sectorial) endorectal probe. The morphologic , quantitative, and echo-pattern changes of the irradiated tumor were exami ned. Results of ultrasound findings before and after radiotherapy and a his tologic examination of the surgical specimens were compared. Histopathologi c studies were used to evaluate macromicroscopical radiation-induced change s, case by case. A comparison between tumoral shrinkage and fibrotic replac ement was made using the semiquantitative Dworak's method. RESULTS: Morphol ogically 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 anore ctal ring in more than 50 percent of the cases. These data had a direct inf luence on surgical treatment. Histologic examination showed that, in 28 out of 29 cases, fibrosis was the most dominant component of the irradiated le sions, 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; t herefore, after radiotherapy, what endorectal ultrasound staged was no long er the tumor but the extent of fibrosis in the rectal wall. A histopatholog ic examination showed that the residual tumor, when present, was always wit hin the fibrosis, never outside or separate from it. Postradiation endorect al ultrasound showed echo-pattern changes. Some of the changes (more echoge nic and nonhomogeneous lesions) were histologically related to the persiste nce of the tumor to a considerable degree; other changes (reappearance of p arietal layers) were related to complete sterilization of lesions in two of three cases. CONCLUSIONS: From the morphologic and quantitative point of v iew, 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 compl etely new concept: that six to eight weeks after radiotherapy, endorectal u ltrasound no longer stages the tumor, but rather the fibrosis that takes it s place. However, postradiation endorectal ultrasound is a valid tool, beca use 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 ultr asound to exclude or indicate complete sterilization of the lesion, the act ual significance of the echo-pattern changes we observed needs to be assess ed further by studies on a large number of cases.