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Esophageal webs are thin, diaphragm-like membranes of squamous mucosa typically in the mid or upper esophagus and may be multiple
May be congenital; also occur with eosinophilic esophagitis, graft-versus-host disease, pemphigoid, epidermolysis bullosa, pemphigus vulgaris
Web plus iron deficiency anemia is known as Plummer-Vinson syndrome
Esophageal rings are smooth, circumferential, thin (< 4 mm) mucosal structures in the distal esophagus at the squamocolumnar junction
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