What is "donuts" here?

Context:

Background Implantation of exfoliated cancer cells has been suggested as a possible mechanism of local recurrence at the site of colorectal anastomosis. Intraoperative rectal washout has been suggested to eliminate free cancer cells; however, there is no conclusive evidence of a beneficial effect of intraoperative rectal washout on local recurrence after anterior resection of rectal cancer.

Methods Studies published through February 2012 evaluating the impact of intraoperative rectal washout for local recurrence or positive cytology from donuts wash were identified by an electronic literature search. A meta-analysis was performed using the DerSimonian-Laird random-effects models to compute risk ratio (RR) along with 95 % confidence intervals (CI).

Results Nine studies met the inclusion criteria, yielding a total of 5,395 patients. Eight studies evaluated overall local recurrence, including anastomotic recurrence, and five of the eight studies evaluated anastomotic recurrence separately. Two studies evaluated positive cytology from donuts wash. Local recurrence rate was 5.79 % in the washout group and 10.05 % in the no washout group—a difference that was statistically significant (RR = 0.57; 95 % CI = 0.46-0.71; P < 0.00001). Rectal washout significantly reduced the risk of anastomotic recurrence (RR = 0.3; 95 % CI = 0.12-0.71; P = 0.007). No influence of rectal washout was observed on positive cytology from donuts wash.

Conclusions From the results of this meta-analysis, it may be justified to recommend intraoperative rectal washout to prevent local recurrence in rectal cancer surgery.