Transrectal ultrasound staging of rectal cancer after preoperative radiotherapy

Background: Transrectal ultrasound (TRUS) has been an accurate preoperative staging modality in rectal cancer. But the experience in post-radiotherapy (RT) TRUS staging is limited and criteria for interpretation differs. The aim of this study was to evaluate the accuracy of the TRUS staging, the imaging characteristics and the necessity of the post-RT TRUS assessment before surgery. Materials and Methods: From October 1992 to April 1995, a total of 42 patients with pathologically proven lower rectal cancer received an initial TRUS examination. All cases were treated by a preoperative irradiation with 3,750 centigray external beam irradiation in 15 frames. Two to three weeks after RT, a second TRUS examination was conducted. The staging parameters used in this study included the tumor depth infiltration (T) and perirectal nodal involvement (N) (TN stage). Results: Accuracy of post-RT TRUS staging was 72%, the over-staging rate was 21%, and the under-staging rate was 7%. Shrinkage, or down-staging, after RT was observed in 52% (22/42) of cases by comparing TN stage of pre-RT TRUS staging with the operative specimen. It included change of tumor depth infiltration (T) in 31% (13/42) of cases and disappearance of perirectal nodal metastasis (N) in 60% (15/25) of cases. Conclusion: For an accurate staging, a second TRUS staging after RT is necessary. Mis-staging of true T2 tumors as T3 stage tumors was a common pattern of over-staging. Disappearance of the perirectal lymph nodes or increased echogenicity with presentation of bright echoic spots in the shrunken perirectal nodes was a reliable sign for negative metastasis after treatment.