The effect of formalin fixation on the size of pelvic sidewall lymph nodes

Although several studies have demonstrated that the size of harvested lymph nodes can be a prognostic predictor in colorectal cancer patients, some considered the size of freshly harvested nodes and others assessed the size after formalin fixation. Because the size change of lymph nodes during fixation has not been fully investigated, we conducted the present study comparing the size of lateral lymph nodes that were surgically harvested from rectal cancer patients, before and after formalin fixation.

A total of 19 consecutive patients diagnosed with rectal adenocarcinoma who underwent total mesorectal excision and dissection of lateral pelvic sidewall lymph nodes were prospectively enrolled. The largest diameters of lymph nodes were measured immediately after manual harvest and after formalin fixation. The ratio of post-fixation size to pre-fixation size and the size difference between pre- and post-fixation were assessed for each lymph node.

The average ratio (± standard deviation) of post-fixation size to pre-fixation size was 0.88 ± 0.40, with median value of 0.8. The size of the lymph nodes decreased by an average of 1.04 mm after fixation, and the median size change after fixation was a 1-mm decrease.

Although measuring lymph node size after formalin fixation can be a viable alternative to measuring the size of fresh lymph nodes before fixation, a 10 to 20% shrinkage or 1-mm size reduction should be considered when interpreting the examination findings.