<prompt> Barretts esophagus is characterised by which of the following histologic change?Squamous metaplasiaIntestinal metaplasiaSquamous dysplasiaIntestinal dysplasia  <response>: Barretts esophagus is a condition in which squamous epithelium of the esophagus is replaced by metaplastic columnar epithelium containing goblet and columnar cells in some patients with GERD. Barretts epithelium is a major risk factor for adenocarcinoma of the esophagus due to proximal displacement of the squamocolumnar junction. In patients with more than 10 year history of GERD should undergo a screening EGD for Barretts esophagus. Endoscopic biopsy is the gold standard for confirmation of Barretts esophagus, and for dysplasia or cancer arising in Barretts mucosa. Ref: Harrisons Principles of Internal Medicine, 18e chapter 291. 