Haemorrhoids: pathology, pathophysiology and aetiology.

Haemorrhoidal disease is the consequence of distal displacement of the anal cushions, which are normal structures with an important role in continence. The causes of haemorrhoidal disease are unknown; constipation and abnormal bowel habit are commonly blamed despite largely contrary evidence. The most consistently demonstrated physiological abnormality is an increased maximum resting anal pressure. Most evidence points to this being a secondary phenomenon rather than the cause of haemorrhoidal disease. Among the many unexplored areas are the function of the longitudinal muscle in relation to haemorrhoidal disease, the description and pharmacological responsiveness of the anal subepithelial muscle, and the clinical role of specific pharmacological agents that might reverse some of the observed physiological changes.