Impact of biopsy on the accuracy of endorectal ultrasound staging of rectal tumors.

PURPOSE

Endorectal ultrasound is a well-established method for the preoperative staging of rectal tumors. This prospective study was performed to establish whether obtaining a biopsy before endorectal ultrasound has an influence on staging accuracy.

METHODS

Between 1990 and 2003, a total of 333 rectal tumors were examined preoperatively by using endorectal ultrasound. All patients underwent rectal resection, and the specimens were sent for histologic evaluation. Thirty-three were not biopsied, the remaining at various times before endorectal ultrasound. The chi-squared test or Fisher's exact test were used for statistical analysis to compare the accuracies.

RESULTS

The overall staging accuracy was 71 percent but differed significantly (P = 0.004) between the groups as a function of time elapsed since biopsy. The best results were seen in tumors that were not biopsied before endorectal ultrasound, which were correctly staged in 85 percent of the cases. The least accurate staging (53 percent) was noted when endorectal ultrasound was performed in the third week after biopsy, mostly as a result of overstaging. Biopsy did not have a significant effect on nodal staging.

CONCLUSIONS

Biopsy before endorectal ultrasound significantly affects its accuracy. To achieve the most accurate staging, biopsy should be performed after endorectal ultrasound. Endorectal ultrasound staging performed in the first week after biopsy is the second best option but should be interpreted with caution in the second or third week.