In acute membranous inflammation, an epithelium becomes coated by fibrin, desquamated epithelial cells and inflammatory cells. An example is the grey membrane seen in pharyngitis or laryngitis due to Corynebaeterium diphtheriae . The term 'pseudomembranous' describes superficial mucosal ulceration with an overlying slough of disrupted mucosa, fibrin, mucus and inflammatory cells. This is seen in pseudomembranous colitis due to Clostridium difficile colonisation of the bowel, usually following broad-spectrum antibiotic treatment. The combination of necrosis and bacterial putrefaction is gangrene.
Gangrenous appendicitis is a good example.