Histological assessment of radiotherapy-induced injury in the anal canal: an exploratory study

Faecal incontinence (FI) is a common and debilitating late effect of chemoradiotherapy in patients with anal cancer. While its clinical relevance is well recognized, the underlying histopathological mechanisms remain poorly understood. This exploratory study aimed to describe structural tissue changes in the anal canal following radiotherapy and assess their potential contribution to FI.

Histological specimens from patients who underwent salvage abdominoperineal excision after chemoradiotherapy for anal cancer (AC group) were compared with those from low rectal cancer patients treated surgically without neoadjuvant therapy (RC group). Degenerative changes were assessed in peritumoral regions, including evaluation of collagen fibre composition via polarized light microscopy and ImageJ software.

Indicative trends were observed, with the AC group showing higher rates of muscle fibre atrophy (73% vs 27%, p = 0.049) and intramuscular edema (78% vs 22%, p = 0.015), and a non-significant increase in lamina propria fibrosis (p = 0.069). No statistically significant differences were found in collagen fibre type distribution. Due to the limited sample size, these findings should be interpreted as descriptive rather than confirmatory.

Radiotherapy appears to induce notable structural alterations within the anal sphincter complex, including muscle atrophy and oedema, which may contribute to post-treatment faecal incontinence. These changes seem independent of collagen fibre composition. Despite the small sample size and lack of clinical data, this study provides preliminary histological insights that warrant further investigation in larger, clinically integrated cohorts.