 Tissue biopsy is not usually required , unless to rule out other suspected conditions such as oral squamous cell carcinoma . The histopathologic appearance is not pathognomonic ( the microscopic appearance is not specific to the condition ) . Early lesions have a central zone of ulceration covered by a fibrinous membrane . In the connective tissue deep to the ulcer there is increased vascularity and a mixed inflammatory infiltrate composed of lymphocytes , histiocytes and polymorphonuclear leukocytes . The epithelium on the margins of the ulcer shows spongiosis and there are many mononuclear cells in the basal third . There are also lymphocytes and histiocytes in the connective tissue surrounding deeper blood vessels near to the ulcer , described histologically as " perivascular cuffing " . 
