Safety margin in anus-saving resection for low rectal cancer

Abstract

The length and method of measurement of the safety-margin below the rectal cancer, being of the utmost importance for its prognosis, is still under debate. The following study was designed and done for its solution.

Light microscopic examination was done on 83 resected rectal cancer specimens to assess the extent of intramural invasion towards the anus. By use of a ruler, the distance between the lower tumour margin and the resection line or the dentate line was measured when the specimen was: 1. freshly resected, 2. after fixing in 10% formalin, and 3. after being mounted in sections. The measurements were compared. By the same method, the distance between the lower tumor margin and the intended resectyion line was measured immediately before resection. It was compared with the measurement immediately after the resection.

In 83 rectal cancer specimens, the extent of intramural infiltration toward the anus was: <-0.5 cm in 75 cases (90.4%). ≥1 cm in 2 cases which showed highly malignant carcinomas. These 2 cases, however, should not have been indicated for anus-saving resection. In 46 fresh specimens, the tumor-resection line distances gave an average of 2.7 cm. After fixing in 10% formalin, they became shortened by 0.7 cm. And, mouting in sections further shortened them by another 0.5 cm, giving a total shortening of 1.2 cm. The tumor-resection line distance in 7 of the 11 fresh specimens resected by the Dixon’s operation was shortened, though never more than o.5 cm immediately the operation.

In performin ganus-saving resection for the low rectal cancer, after full isolation the rectum and stretching it slightly, ≥3 cm of the rectum distal to the lower tumor margin should be resected. A safety margin of more than 2.5 cm is necessary in the fresh specimen. If formalin fixed specimen is measured, the safety margin should be ≥2 cm.