Pseudomembranous enteritis occurs mainly in the colon and occasionally in the small intestine and other areas. The lumen of the diseased intestine is dilated, with increased fluid in the lumen. Visual observation of the diseased intestinal mucosa reveals coagulative necrosis covered with scattered yellowish-white pseudomembranes of varying sizes, ranging from several millimeters to 30 mm. In severe cases, the pseudomembranes may fuse into patches, and large and small exposed areas of pseudomembranes may be seen. Microscopically, the pseudomembrane is composed of fibrin, neutrophils, monocytes, mucin, and necrotic cell debris. The lamina propria was infiltrated by neutrophils, plasma cells and lymphocytes, and in severe cases the glands were disrupted and necrotic. The submucosal layer is thickened by inflammatory exudation with vasodilation, congestion and microthrombosis. The necrosis is generally limited to the mucosal layer, but in severe cases it may extend to the submucosal layer, occasionally involving the whole intestinal wall and leading to intestinal perforation. Wang Zhimin, Department of Anorectology, Shandong Qianfo Mountain Hospital
Price and Davies divided the mucosal lesions of this disease into 3 types.
(i) early mild lesions showing focal necrosis of the mucosa, infiltration of neutrophils and eosinophils in the lamina propria and fibrin exudation.
The more severe lesions show glandular destruction, surrounding neutrophilic polymorphonuclear cell infiltration with typical volcano-like elevated necrotic lesions and pseudomembrane formation. Both of these lesions are limited to superficial areas of the mucosal lamina propria, with normal mucosa between them.
(iii) The most severe lesion is a complete destruction of the mucosal structure with extensive rippling of the lamina propria, covered with thick fused pseudomembranes. After the lesion heals, the pseudomembrane is shed, and the healed wound under the pseudomembrane is red, and the endoscopy can be completely normalized about 10 days after the pseudomembrane is shed.