What is the most accurate method of diagnosing specialized columnar epithelium in Barrett's mucosa?
M.I.F. Canto (Baltimore)
Barrett's esophagus is defined as the metaplastic replacement of normal squamous epithelium in the esophagus by specialized columnar epithelium (SCE) . Although other types of epithelia have been described in patients with Barrett's esophagus (i.e. junctional- and fundic-type) , SCE is considered the pathognomonic and most clinically relevant epithelium due to its association with adenocarcinoma of the esophagus and esophagogastric junction . Hence, the most accurate or "gold" standard method for the diagnosing SCE in Barrett's esophagus is the recognition of intestinal-type mucosa (similar to the incomplete type of gastric intestinal metaplasia [1, 4]) with characteristic crypts and villi lined by mucus-secreting columnar cells and goblet cells in histologic specimens. The diagnosis of SCE in biopsies is facilitated by the identification of goblet cells that contain acidic mucin, which stains positively with Alcian blue at pH 2.5 .
SCE in Barrett's esophagus can be diagnosed at the time of endoscopy. The presence of more than two-three centimeters of salmon-pink columnar-type mucosa above the esophagogastric junction can suggest the presence of Barrett's esophagus and SCE. However, technical problems with accurately delineating the junction between the stomach and the esophagus during endoscopy can result in inconsistencies in the ability to detect SCE . Furthermore, endoscopic measurement of the extent or length of columnar mucosa above the esophagogastric junction is also imprecise . Even greater confusion arises with inadvertent biopsy of intestinal metaplasia in the gastric cardia or at the esophagogastric junction , which may be present in up to 18% of patients without endoscopically apparent Barrett's esophagus undergoing elective upper endoscopy. It is not known whether SCE at the cardia or esophagogastric junction carries the same clinical relevance and implications as SCE in the esophagus .
Alternative methods for diagnosing SCE in Barrett's esophagus have been described. In 1995, Fennerty et al. described the use of balloon cytology to allow an non endoscopic diagnosis . They used a Brandt esophageal cytology balloon catheter in 10 unselected patients with Barrett's esophagus prior to endoscopy and biopsy. Unfortunately, no patient had a positive cytologic specimen with goblet cells and/or dysplasia. Although balloon cytology is a promising screening test because of its low cost and safety, this small pilot study  suggests that its sensitivity for the diagnosis of SCE may be unacceptably low.
There has been increased interest in the use of vital staining during endoscopy to improve the detection of Barrett's esophagus. Investigators have used Lugol's iodine to diagnose Barrett's esophagus [9, 10]. The problem with iodine is that it merely enhances the contrast between normal squamous and nonsquamous or malignant squamous esophageal mucosa. It does not delineate SCE from non-SCE in Barrett's esophagus, be it squamous, gastric junctional or fundic epithelium. Methylene blue reversibly stains actively absorbing cells (i.e. intestinal-type mucosa)  such as gastric intestinal metaplasia  and SCE in Barrett's esophagus. We recently demonstrated in a recent pilot study that staining with methylene blue at the time of endoscopy is a safe, reproducible, inexpensive and highly accurate (95%) method of identifying SCE in Barrett's esophagus, including cells with dysplasia . The sensitivity, specificity, positive and negative predictive value of methylene blue staining was 95%, 97%, 98%, and 92%, respectively . We also showed that the accuracy of methylene blue staining for SCE in a larger prospective in vivo and ex vivo study using endoscopic biopsies and surgically-excised esophageal specimens was 92% and 93, respectively . SCE comprised the majority of cells in stained biopsies and the mean proportion of SCE in stained biopsies (87%) was significantly higher than in unstained ones (0.05%, p < .00001) . Methylene blue staining can therefore be used as an adjunct to endoscopic biopsy; i.e. to direct biopsies towards focal areas of SCE in Barrett's esophagus. Indeed, methylene blue staining led to a new diagnosis of Barrett's esophagus in 5 of 12 (42%) patients with no history of SCE. In a prospective, controlled sequential trial, methylene-blue staining led to a much larger proportion of SCE in endoscopic biopsies compared to random biopsy (p = .0006), especially in patients with limited-segment (54% vs 94%) and long-segment BE (72% vs 92%).. Taken together, these data indicate that methylene blue staining is a promising, highly accurate adjunct to endoscopic biopsy in detecting SCE in Barrett's esophagus.
Finally, other biological markers may ultimately be applicable in the clinical setting to aid in the diagnosis of SCE. SCE in Barrett's esophagus appears to lack well-defined brush borders and intestinal brush border enzymes, unlike normal intestinal absorptive cells and intestinal metaplasia of the stomach . However, using reverse transcription polymerase chain reaction (PCR) and immunohistochemistry, Wu et al. showed that the intestinal disaccharidase sucrase-isomaltase enzyme is present in 76% of Barrett's epithelium . In the future, diagnostic tests such as in situ hybridization and PCR which identify specific cellular markers might improve the accuracy of diagnosing SCE in patients with Barrett's esophagus.
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