Accuracy of endosonography in the staging of rectal cancer treated by radiotherapy.

Endosonography is the best available method for the pretherapeutic staging of rectal cancer. The present prospective study was to determine the influence of previous radiotherapy, widely used in the management of this tumour, on the accuracy of endosonography. A complete endosonographic examination was performed just before surgery in 40 patients with rectal cancer. Endosonographic and pathological staging were compared in group A, 21 patients without previous radiotherapy, and group B, 19 patients with preoperative radiotherapy. While the endosonographic accuracy for lymph node involvement was similar in the two groups (85 per cent compared with 84 per cent), wall invasion was correctly ascertained in 86 per cent in group A but in only 47 per cent in group B (P less than 0.05). After irradiation, the thickening of the rectal wall and the poor visualization of the hyperechoic layers hampered interpretation. Post-radiotherapy inflammation and/or fibrosis probably explained the echographic changes. Radiotherapy therefore altered endosonographic staging of rectal cancer. New interpretation criteria are needed for evaluation and follow-up of rectal cancer treated by radiotherapy.