Zenker's diverticulum pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Ajay Gade MD[2]]

Overview

Zenker's diverticulum (ZD) is thought to occur due to the result of motor abnormalities of the esophagus. A defect over the Killian's triangle, a point of weakness in the muscular wall of the hypopharynx results in ZD. Killian's triangle is surrounded by the cricopharyngeal sphincter and oblique fibers of the inferior constrictor of the pharyngeal muscle. It is considered a pseudodiverticulum as it includes only mucosa and submucosa. Chronic strain on the Killian's triangle leads to an evagination of the sphincter, which may be because of the high pressures caused by the food bolus in the course of swallowing and the abnormalities of the upper esophageal sphincter (UES). This failure to achieve adequate diameter for effective bolus clearance leads to a subsequent increase in the hypopharyngeal pressure gradient. Increased intra-bolus pressures found in patients with ZD can be secondary to impaired bolus passage combined with the gastroesophageal reflux disease (GERD) or as a result of the GERD. As the diverticulum enlarges, it may compress the pharyngoesophageal segment as well as increased stiffness and the intra-bolus pressure. Increased intra-bolus pressure is also increased in older patients who perform multiple swallows to achieve bolus clearance. Acid reflux is thought to lead to increased spasm of the UES which in turn increases the intra-bolus pressures during swallowing, given that swallowing is frequently distinct from episodes of acid reflux disease.

Pathophysiology

The pathophysiology of the Zenker's diverticulum is as follows

Killian's dehiscence

• Zenker's diverticulum (ZD) is thought to be due to the result of motor abnormalities of the esophagus.
• ZD is a defect over the Killian's triangle, a point of weakness in the muscular wall of the hypopharynx.
• Killian's triangle is surrounded by the cricopharyngeal sphincter and oblique fibers of the inferior constrictor of the pharyngeal muscle.
• ZD should be considered a pseudodiverticulum as it includes only mucosa and submucosa.

Chronic straining

• Chronic strain on the Killian's triangle leads to an evagination of the sphincter, which may be because of the high intra-luminal pressures caused by the food bolus in the course of swallowing and the abnormalities of the upper esophageal sphincter (UES).
• This failure to achieve adequate diameter for effective bolus clearance leads to a subsequent increase in the hypopharyngeal pressure gradient.
• Increased intrabolus pressures found in patients with ZD can be secondary to impaired bolus passage combined with the gastroesophageal reflux disease (GERD) or as a result of the GERD.

Enlargement of Zenker's diverticulum

• As the diverticulum enlarges, it may compress the pharyngoesophageal segment as well as causing increased stiffness and the intrabolus pressure.
• Increased intrabolus pressure is also increased in older patients who perform multiple swallows to achieve bolus clearance.

Hypotheses for mechanism of development of Zenker's diverticulum

• Various hypothesis involved in the pathogenesis of the Zenker's diverticulum are as follows

1. Zenker's diverticulum is a disorder of diminished upper esophageal sphincter, incomplete sphincter opening is probably the cause of dysphagia. Increased hypopharyngeal pressures throughout swallowing are probably important in the pathogenesis of the diverticulum.
2. The nemaline bodies and red ragged fibers are usually the normal cricopharyngeous findings, whereas the Zenker's diverticulum is characterized by adipose tissue deposition and degeneration of the fiber these structural modifications can impair the UES opening and dysphagia ensues.
3. The pharyngeal pouches are not a purely localized incoordination of the cricopharyngeal sphincter but are associated with a generalized esophageal muscle dysfunction.
4. Acid reflux induces longitudinal esophageal shortening, which in turn increases the chance for the development of herniation between two spatially associated structures, the pharyngeal constrictors and cricopharyngeus muscles, leading to the development of Zenker diverticulum.
5. Zenker's diverticulum is thought to result from disordered coordination among the pharynx and upper esophageal sphincter.
   • Manometric studies of the upper esophagus were used in testing the hypothesis of dysmotility in the formation and growth of a Zenker's diverticulum; however, the data have provided conflicting evidence.
   • Manometric studies show that resting upper esophageal sphincter strain is normal in some patients with Zenker's diverticulum and decreased in others. Abnormal premature relaxation and contraction of the upper esophageal sphincter seen in some patients with Zenker's diverticulum may be accompanied with the aid of pharyngeal contractions against a closed sphincter.
   • This abnormality is thought by a few investigators to be the cause of Zenker's diverticulum, but not by others who have found normal upper sphincter relaxation.
6. In summary, in-coordination of pharyngeal contraction and UES opening has also been variably demonstrated by some investigator.

Abnormal esophageal motility

• All the above-mentioned hypotheses lead to herniation within the Killian's triangle, inclusive of disorders associated with altered UES function, unusual esophageal motility, esophageal shortening.
• This leads to the creation of a sac with a narrow neck that can trap liquid and food, the distended sac may compress the cervical esophagus.
• Impaired bolus passage leads to increases intra-bolus pressure which leads to herniation in the Killian's triangle.

Role of acid reflux

• Acid reflux is thought to lead to increased spasm of the UES which in turn increases the intrabolus pressures during swallowing, given that swallowing is frequently distinct from episodes of acid reflux disease.

Gross Pathology

On gross pathology, esophageal diverticulum or a sac are characteristic findings of Zenker's diverticulum.

Microscopic Pathology

On microscopic histopathological analysis, Zenker's diverticulum presents with the following findings:

• Psuedo diverticulum
• Only mucosa and submucosa present
• Chronic submucosal inflammation
• Epithelial atypia or dysplasia
• Squamous cell carcinoma of esophagus (in advanced cases)

Source:Librepathology </gallery>

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