Atresia refers to defects caused by the incomplete formation of a lumen. Many hollow organs originate as strands and cords of cells whose centers are programmed to die, thus forming a central cavity or lumen. Atresia of the esophagus is characterized by partial occlusion of the lumen, which was not fully established in embryogenesis. Dysplasia (choice C) is caused by abnormal organization of cells into tissues, which is a situation that results in abnormal histogenesis. Tuberous sclerosis is a striking example of dysplasia, in which the brain contains aggregates of normally developed cells arranged into grossly visible "tubers." Ectopia (choice E) is an anomaly in which an organ is outside its normal anatomic site.Diagnosis: Esophageal atresia