Diverticula of the esophagus are generally classified into two varieties: the traction type and the pulsion variety. The former may occur at any part of the esophageal tube as a result of traction or a "pulling effect" by some chronic organic disease in the chest, such as tuberculous tracheobronchial glands, mediastinitis or vertebral caries. The latter usually occurs at the pharyngo-esophageal junction and is formed by a protrusion or "pushing" backward of the undefended triangular space, bounded above by the lower margins of the inferior constrictors, and below by the superior border of the posterior wall of the esophagus. This triangular area is frequently referred to as the "pharyngeal dimple" and consists of mucous membrane and submucosa. The inconstancy of muscle fibers at this site is a predisposing factor of pressure diverticula. Pulsion-traction diverticula are also described by some authors.
The pressure diverticulum usually passes down