The role of lymphatics in the pathogenesis of pneumatosis in experimental bowel ischemia.

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.