Pathology of the rectal wall in solitary rectal ulcer syndrome and complete rectal prolapse

Background-The aetiology and pathology of rectal prolapse and solitary rectal ulcer are poorly understood. Aims-To examine the full thickness rectal wall in these two conditions. Methods-The pathological abnormalities in the surgically resected rectal wall were studied from nine patients with solitary rectal ulcer syndrome, 11 complete rectal prolapse, and nine cancer controls. Routine haematoxylin and eosin and Van Gieson staining for collagen were performed. Results-The rectal wall from solitary rectal ulcer syndrome specimens was thickened compared with complete rectal prolapse and controls. The major difference was in the muscularis propria (2.2 v 1.1 v 1.2 mm, medians, p<0.005) and particularly the inner circular muscular layer, and to a lesser extent the submucosal and outer longitudinal muscular layers. Some solitary rectal ulcer syndrome specimens showed unique features such as decussation of the two muscular layers (four of nine), nodular induration of inner circular layer (four of nine) and grouping of outer longitudinal layer into bundles (three of nine); these were not seen in complete rectal prolapse or control specimens. Conclusions-These features, which resemble the features of high pressure sphincter tissue, may be of aetiological importance, and suggest a different pathogenesis for these two disorders. Excess collagen was seen in both disorders, was more severe in solitary rectal ulcer syndrome specimens, and probably reflects a response to repeated trauma.