Association between pathologic features of peripheral nerves and postoperative anal function after neoadjuvant therapy for low rectal cancer

Purpose: Neoadjuvant chemoradiotherapy (CRT) for rectal cancer improves local control but also induces severe postoperative anal dysfunction that may be related to neural degeneration. The aims of the study were to identify pathological features of neural degeneration caused by neoadjuvant CRT or neoadjuvant chemotherapy (NAC) and to evaluate the association between neural degeneration and anal function.

Methods: A retrospective study using chronologically different groups was performed in 95 patients with rectal cancer treated with curative resection with neoadjuvant CRT (n = 47), NAC (n = 27), or surgery alone (no neoadjuvant therapy) (n = 21) at National Cancer Center Hospital East from 2001 to 2014. Peripheral nerve degeneration was evaluated histopathologically using H&E stained sections, based on karyopyknosis, vacuolar or acidophilic degeneration, denucleation, adventitial neuron change, and fibrosis. Morphological analysis of peripheral nerves was compared among the three groups. The association between pathological features and anal function (Wexner Score) was evaluated.

Results: After CRT, the degree of fibrosis around the tumor was severe, and neural degeneration was found in peripheral neurons. With NAC and surgery alone, there was little fibrosis and neural degeneration. Pathological changes after CRT were more pronounced than those after NAC, indicating greater tissue degeneration due to CRT. There was an association between anal function and degeneration score in the CRT group, but not in the other groups.

Conclusions: Peripheral nerves in patients who received neoadjuvant CRT showed characteristic pathological features indicating greater degeneration, compared with patients who received NAC. Neural degeneration is associated with anal function and several pathological factors after CRT.