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 Patients with intractable constipation can be divided into those who have a normal diameter gut and those who have gut dilatation. The latter include patients with Hirschsprung's disease, chronic idiopathic intestinal pseudoobstruction and idiopathic megacolon or megarectum. The last conditions of an idiopathically dilated colon and/or rectum appear to be clinically heterogenous, are very uncommon, and hence are often poorly managed.This study aimed to characterise these conditions clinically. A large series of patients was defined precisely from the clinical, operative, and pathological aspects, by retrospectively studying all patients who underwent surgery at one hospital for these conditions over a 23 year period. To establish the clinical spectrum of all patients with this condition, including outcome, and to evaluate them consistently, we have also prospectively studied all patients with idiopathic megarectum or megacolon referred to the same hospital over a three year period. MethodsIn both the retrospective and prospective part of this study patients were divided into those with idiopathic megarectum (including a variable degree of sigmoid colon dilatation), total rectal and colonic dilatation, or megacolon with a normal size rectum.' RETROSPECTIVE STUDY OF OPERATED PATIENTSThe notes of patients classified as having idiopathic megarectum or megacolon who had surgery between 1968 and 1991 were reviewed. Patients were included only if the gut

Background-The aetiology and pathology of both idiopathic megarectum and idiopathic megacolon are unknown. In particular, it is unknown whether there are abnormalities involving enteric nerves or smooth muscle. Methods-Resected tissue was examined from 24 patients who underwent surgery for idiopathic megarectum, from six patients who had tissue resected for idiopathic megacolon, and 17 control patients who had surgery for non-obstructing large bowel cancer. Qualitative and quantitative histological examination was performed after staining with haematoxylin and eosin, periodic acid SchiV (PAS), Martius scarlet blue (MSB), and phosphotungstic acid haematoxylin (PTAH). Neural and glial tissue were examined after immunostaining with S100 and PGP9.5. Results-Compared with controls, patients with idiopathic megarectum had significant thickening of their muscularis mucosae (median 78 v 33 µm, p<0.005), circular muscle (1000 v 633 µm, p<0.005), and longitudinal muscle (1083 v 303 µm, p<0.005), despite rectal dilatation. This thickening was relatively greater in the longitudinal than in the circular muscle. Fibrosis of the longitudinal muscle was seen, using MSB staining, in 58%, of circular muscle in 38%, and of muscularis mucosae in 29% of patients. The relation between muscle thickening and fibrosis was variable. The density of neural tissue in the longitudinal muscle seemed to be reduced in patients with idiopathic megarectum. There was no thickening of enteric muscle or alteration in the density of innervation in patients with idiopathic megacolon. Conclusion-There is notable thickening of the enteric smooth muscle in patients with idiopathic megarectum, but the architecture of the enteric innervation seems to be intact. Functional abnormalities of the latter remain a possible cause of the smooth muscle hypertrophy.

Most laxatives, if used intermittently in the absence of contraindications, are relatively safe. Bulking agents may diminish absorption of some minerals and drugs, but this is not usually clinically significant. Ispaghula can cause serious allergic reactions. The chronic ingestion of stimulant laxatives has been blamed for the development of the 'cathartic colon', but there are no definitive studies which have demonstrated this. Dantron (danthron) preparations should only be used in older patients and the terminally ill because of the risk of hepatotoxicity with this drug. Oral oxyphenisatine should no longer be used. Senna would appear to be the stimulant laxative of choice during pregnancy and lactation. Bisacodyl is the polyphenolic derivative of choice. Lactulose, sorbitol and lactilol rarely cause significant adverse effects. Magnesium salt laxatives and phosphate enemas can cause serious metabolic disturbances in babies and young children. Liquid paraffin is contraindicated if there is any risk of aspiration. Interference with the absorption of fat soluble vitamins would not appear to be clinically significant. Docusate sodium may potentiate the hepatotoxicity of other drugs, but reports of this are rare. The role of cisapride in constipation has not been established. Antidiarrhoeal drugs are second line drugs whose use is aimed at minimising inconvenience and discomfort. No antidiarrhoeals can be recommended for children under 4 years of age. Loperamide is the drug of choice in older children and adults. The atropine component of diphenoxylate/atropine combinations can cause significant adverse effects. Bismuth salicylate is an inconvenient treatment for travellers' diarrhoea as large frequent doses of the liquid formulation are needed. Some bismuth can be absorbed and there is the potential to cause encephalopathy. Octreotide, methysergide and cholestyramine have a role for specific causes of diarrhoea only. Octreotide is effective in high output states from the small or large bowel, with few adverse effects. Clonidine and lidamidine may have a role in the treatment of chronic diabetic diarrhoea. The role of lidamidine in nondiabetic chronic diarrhoea has not been established.

Variable changes in innervation, and an abnormal contractile protein immunoreactivity pattern in one patient, may be of pathogenic importance. These clinically homogeneous conditions are likely to be due to a range of underlying pathogenic abnormalities. A search for further specific biochemical abnormalities is justified.

We have studied the resection specimens from 5 patients with idiopathic megarectum and megacolon and 10 control subjects with non-obstructing colonic cancer. Histological staining with haematoxylin and eosin, and immunocytochemical staining for protein gene product 9.5 (PGP9.5), S100 protein, vasoactive intestinal polypeptide (VIP) and calcitonin gene-related peptide (CGRP), and histochemical localization of NADPH diaphorase was performed. The amount of VIP and CGRP present in samples was measured using an enzyme-linked immunosorbent assay. Patients with idiopathic megarectum and megacolon showed hypertrophy of the muscularis mucosae and muscularis externa. The architecture of the innervation as assessed by immunoreactivity for PGP9.5 and S100 protein appeared normal. There was a decrease in the density of innervation of the longitudinal muscle in rectal tissue from patients with idiopathic megarectum, with fewer VIP- and NADPH-diaphorase-containing nerves. In the muscularis mucosae and lamina propria of the rectal samples of patients with idiopathic megarectum, VIP immunoreactivity was higher and more NADPH-diaphorase-containing nerves were seen. CGRP-immunoreactive nerve fibres were only seen in the myenteric plexus. No CGRP-immunoreactive cell bodies were seen. In summary, there is an increase in VIP and nitric oxide containing fibres in the muscularis mucosae and lamina propria and a decrease in the longitudinal muscle in rectal tissue of patients with idiopathic megarectum. Both are NANC (nonadrenergic noncholinergic) inhibitory transmitters in the gut and the possible relationship of the changes in their density with gut function is discussed.