Methylene blue
Stains used in chromoendoscopy have three major mechanisms. Absorptive stains have an affinity for particular mucosal elements, and include Lugol's iodine, methylene blue, toluidine blue and crystal violet (gentian violet) . Lugol's iodine specifically stains non-keratinized squamous epithelium, and consequently is useful for identifying squamous tissue, squamous dysplasia and squamous cell carcinomas. Methylene blue stains absorptive epithelium and is useful for identifying abnormality in the small intestine and colon. Barrett's esophagus involves change in the mucosa of the esophagus into a tissue that includes glands (intestinal metaplasia), and as a result, can be identified with methylene blue staining. Also, methylene blue has been used to identify dysplasia in patients with ulcerative colitis. Toluidine blue stains nuclei of malignant cells blue, and is used in oral and esophageal squamous cell carcinoma. Crystal violet is absorbed into intestinal and neoplastic cells and is used to identify Barrett's esophagus and colonic neoplasms.