Narrowing of the oesophagus can be due either to stricture formation (benign or malignant), webs (mucosa and submucosa only), and rings (mucosa, submucosa and muscle), or from external compression from other structures in the neck or mediastinum.
This is a companion discussion topic for the original article at https://patient.info/doctor/gastroenterology/oesophageal-strictures-webs-and-rings