**2.2 Constipation of functional obstructed defecation**

Constipation of functional obstructed defecation may be associated with anismus or dyssynergic pelvic floor, megarectum, Hirschsprung's disease, and descending perineum syndrome. Anismus is characterized as a pelvic floor dysfunction. The puborectalis muscle and external anal sphincter fail to relax or paradoxically contract during straining to defecate leading to a difficult or impossible defecation. Dyssynergic pelvic floor is characterized by incoordination of the abdominal, rectoanal, and pelvic floor muscles leading to difficult or incomplete evacuation. The pathophysiological mechanism of persistent constipation is the failure of the anorectal angle to open, of the perineum to descend and of the anal canal to shorten as a result of sustained contraction of the puborectalis muscle [17]. Megarectum is a rare condition that is differentiated from Hirschsprung's disease with rectal biopsies. Patients with megarectum often suffer from constipation (fecal impaction). In these cases there may be an impaired rectal sensation and high distensibility. In addition, impaired rectal sensation and ignoring or resisting the physiological urge to defecate lead to accumulation of more stools in the rectum, which are difficult and painful to expel [18]. Hirschsprung's disease is another type of pelvic outlet obstruction which is characterized by absence of rectoanal inhibitory reflex. Aganglionosis leads to loss of internal anal sphincter relaxation when the rectum is distended [19, 20]. Descending perineum syndrome is characterized

by a persistent and intractable difficulty to defecate. Abnormal perineal descent during straining to defecate is probably secondary to injury to pudendal and sacral nerves from trauma, childbirth, or chronic straining at defecation [21, 22].
