Clinical features of idiopathic megarectum and idiopathic megacolon

Background - Dilatation of the rectum and/or colon, in the absence of demonstrable organic disease, is an uncommon and poorly characterised condition. Aims To characterise the clinical and diagnostic features, and response to treatment, of patients with idiopathic megarectum (IMR) and idiopathic megacolon (IMC). Methods - A retrospective review was undertaken of all patients operated on for these conditions over a 23 year period. In addition all patients treated over a three year period were prospectively studied by means of a questionnaire, contrast studies of the upper and lower intestine, spine x rays to exclude spinal dysraphism, anorectal physiological studies, and assessment of clinical outcome. Patients with Hirschsprung's disease and other known causes of gut dilatation were excluded. Results - (i) Retrospective study: Of 63 operated patients, 22 had IMR, 23 had IMR and IMC, and 18 had IMC only. Five patients with IMC had previous sigmoid volvulus, and three had associated nongastrointestinal congenital abnormalities. Faecal incontinence was always associated with rectal impaction and 14 patients (82%) with IMR alone had had manual disimpaction. (ii) Prospective study: Twenty two patients had IMR, with a median rectal diameter of 10 cm (normal <6.5 cm). Six patients had IMC and one patient had LMR and IMC. Patients with IMR were significantly (p=0.0007) younger than patients with IMC. All patients with IMR became symptomatic in childhood, compared with half the patients with IMC who developed symptoms as adults. Patients with IMR all presented with soiling and impaction, compared with patients with IMC whose symptoms were variable and included constipation or increased bowel frequency, pain, and variable need for laxatives. No upper gut dilatation was seen in either group of patients. Spinal dysraphism was seen in two of 18 patients with IMR and two of four with IMC, suggesting extrinsic denervation as a possible cause in a minority. Twelve of 22 patients with IMR had a maximum anal resting pressure below normal, indicating sphincter damage or inhibition. Both IMR and IMC patients had altered rectal sensitivity to distension, suggesting that despite lack of dilatation the rectum in IMC has altered viscoelasticity, tone, or sensory function. Fifteen of 22 patients with IMR were successfully managed with laxatives or enemas, but seven required surgery, Two of seven patients with IMC required surgery, including one for sigmoid volvulus. Conclusions - Patients with IMR differ clinically, diagnostically, and in their outcome from patients with IMC. These conditions demand specific investigation, and intensive treatment, to achieve optimum care.