Perineural invasion and micrometastasis around autonomic nerves in rectal carcinoma

The purpose of this study was to clarify the frequency of perineural invasion and micrometastasis around autonomic pelvic nerves, and histopathological features and prognosis of cases with micrometastasis. Autonomic pelvic nerves with surrounding connective tissue (autonomic nerve specimen) were dissected from the resected specimen in 50 rectal cancer cases that underwent combined resection of autonomic nerves. Autonomic nerve and resected specimens were examined histopathologically. Perineural invasion of the resected specimen was confirmed in 5 of 50 cases (10%), but perineural invasion was not observed in the nerve specimens. Micrometastasis in the small nodes or fatty tissue around the autonomic nerves were detected in 10% of the cases. Micrometastasis had a tendency to occur more often in more than pT3 cases than in less than pT2 cases (p=0.07). Tumor occupying more than half a lumen or perineural invasion positive cases in the resected specimen had micrometastasis more often than tumors occupying less than half a lumen or perineural invasion negative cases, though these factors were not statistically significant. However, cases with micrometastasis around the pelvic nerves were considered to have high risk of recurrence as all cases with micrometastasis died in 3 years 5 months after surgery. A case with micrometastasis of nerves other than the pelvic nerves had better prognosis.