Lymph node preparation in resected colorectal carcinoma specimens employing the acetone clearing method.

For the histopathological evaluation of resected colorectal carcinoma specimens, the currently required minimum number of lymph nodes that need to be examined to ensure accurate staging is 12. In some cases, however, this number of lymph nodes cannot be obtained by the conventional preparation method, based on formalin-fixed fatty tissue. Since prognostic accuracy correlates with the number of lymph nodes examined, a repeat work-up of the fatty tissue after soaking in acetone for 24h is a means of achieving the required minimum of 12 lymph nodes in many cases. Our department, which deals with an average of 307 colorectal cancer resection specimens per year, received between May 2004 and November 2006 80 cases (10.4%) in which the number of detected lymph nodes was less than 12. Owing to the use of conventional preparation methods, the required number of 12 lymph nodes could not be found, and subsequent acetone clearance of fatty tissue for a repeat examination was carried out. On average, 4.4 additional lymph nodes having an average size of 2mm were discovered. Accessory lymph node metastases were found in 9 cases. In 2 of these, the UICC classification had to be revised. In 1 case, a lymph node metastasis was detected after acetone clearance in an initially nodal negative carcinoma. Acetone clearance is an appropriate option to identify accessory lymph nodes in colorectal carcinoma specimens for daily routine use, and also constitutes an excellent instrument for internal quality control.