Search

Previous in vitro studies have suggested that successful neural crest cell migration in the developing gut could be influenced by the composition of the extracellular matrix components, tenascin and fibronectin. The authors aimed to gain insight into the pathogenesis of Hirschsprung's disease (HD) by studying the distribution of tenascin and fibronectin in bowel specimens of patients with HD. Immunohistochemical examination was performed in specimens from 10 HD patients (8 aganglionic, 5 transitional, and 10 normoganglionic zones) and 18 age- and site-matched controls undergoing other types of gastrointestinal surgery. The distribution of tenascin was restricted to the basement membranes of the smooth muscle and vasculature, and in the basement membranes surrounding neuronal ganglia in all the controls and in 10 proximal normoganglionic HD specimens. More intense tenascin immunofluorescence was observed in the smooth muscle basement membranes of the muscularis externa of eight aganglionic and five transitional zones of HD. Wide-spread distribution of fibronectin was found in all the basement membranes as well as in the lamina propria and submucosa of all control and 10 normoganglionic HD sections. However, more intense immunofluorescence with fibronectin was observed in all the layers of eight aganglionic and five transitional zones of HD specimens. The present findings show that the mesenchymal and basement membrane extracellular matrix constitution is abnormal in the affected bowel of HD. Although a causal relationship has not been demonstrated, corroborative evidence from earlier animal experiments in other studies suggests that the extracellular matrix abnormalities may contribute to the pathogenesis of HD.

Previous immunohistochemical studies have shown an abnormal distribution of extracellular matrix (ECM) proteins, including laminin, in the smooth muscle layer of muscularis externa in Hirschsprung's disease (HD) bowel. These findings supported the hypothesis that an abnormal ECM microenvironment may be responsible for the failure of migration and/or development of the neural crest cells in the gut in HD. In order to determine the cause of the abnormality in laminin distribution, solid-phase enzyme-linked immunosorbent assays and immunoblots were used to quantitate the ECM protein laminin and characterize its subunits, respectively, in extracts of the dissected smooth muscle layer of the muscularis externa. In the aganglionic bowel, laminin (median concentration, 32.4 ng/mg of tissue) was found to be present in significantly greater quantity than in both the normoganglionic bowel of the same specimen (median, 17.2 ng/mg, P less than or equal to .05) and the normal bowel of age-matched controls (median, 9.7 ng/mg, P less than or equal to .05). Laminin concentration was also found to be significantly higher in normoganglionic HD bowel (median, 17.2 ng/mg) than in age-matched control specimens (median, 10.8 ng/mg, P less than or equal to .05). No difference was observed in the subunit composition of laminin in HD and control extracts analysed by immunoblot after polyacrylamide gel electrophoresis. This study demonstrates a quantitative abnormality of laminin in the bowel in HD, supporting the hypothesis that "abnormal microenvironment" may have a role in the pathogenesis of HD.

Two infant boys with megacystis microcolon intestinal hypoperistalsis syndrome (MMIHS) are reported. Presenting with neonatal intestinal obstruction, they underwent laparotomies that showed megacystis, microcolon, and aperistaltic shortened small bowel without any mechanical obstruction. Patient 1 gradually improved and is developing normally at home, on a normal diet without genitourinary or gastrointestinal complaints (now 11 years old). Patient 2, who underwent vesicoamniotic drainage antenatally, never developed adequate gastrointestinal or genitourinary function in spite of appropriate diversion and pharmacologic support. He showed progressive deterioration and died at the age of 7 months. Detailed histo-immuno- and ultrastructural pathology assessment, although confirming results in the existing literature in some aspects, showed previously unreported neuronal dysplastic changes associated with increased laminin and fibronectin. Although patient 1 showed ultrastructural features of vacuolar degeneration of smooth muscle as reported in the literature, patient 2 showed ultrastructural and histochemical evidence of excessive smooth muscle cell glycogen storage with severely reduced contractile fibres displaced to the extreme periphery of the cells, suggesting a fundamental defect of glycogen-energy utilization. A deficiency of fiber synthesis as the alternative primary defect is discussed. In both cases, a two-step genetic defect may explain the variability in clinical outcome and pathological findings.

Twelve spontaneously delivered, normally suckled, small-for-gestational-age (weighing 756 to 1,213 g) neonatal piglets were used to assess the role of the mesenteric vasculature in the pathogenesis of neonatal necrotizing enterocolitis (NEC) by producing intestinal ischemia. Component vessels (arteries, veins, lymphatics) of the mesenteric vascular arcades were variously occluded by ligation for 48 hours. Nine adjacent vessels of the same type or nine adjacent combinations of vessels were occluded in piglets 12 to 18 hours postpartum. Arterial plus lymphatic ligation induced lesions showing the complete histopathological spectrum of NEC (mucosal stripping, hemorrhage, submucosal disruption and destruction, full-thickness necrosis, inflammatory infiltration) including pneumatosis intestinalis. Two of the lowest birth weight animals produced complete NEC in response to lymphatic ligation alone. A condition consistent with "prepneumatosis" was found when lymphatics only were ligated. The distended lymphatic vessels in the submucosa resembled pneumatosis with reference to shape size and distribution, but contained milk-derived lipids, some proteins and lymph but no gas. Arterial ligation alone induced NEC-like lesions without pneumatosis. Venous ligation alone induced minor congestive/hemorrhagic lesions. Pneumatosis appears to originate in the lymphatic vessels of the submucosa in this experimental model of NEC. Lymphatic occlusion alone can cause complete NEC in very SGA neonatal piglets. Arterial plus lymphatic occlusion produces a unique combination of specific pathology resembling human NEC.