What are the A ring and B ring in the esophagus?

Esophageal A Ring and B Ring: Anatomic Definitions

The B ring (Schatzki ring) is a clinically significant annular constriction at the gastroesophageal mucosal junction covered proximally by squamous epithelium and distally by gastric mucosa, while the A ring is a less common muscular ring located at the junction of the tubular esophagus and esophageal vestibule, approximately 2 cm above the B ring. 1, 2

Anatomic Location and Structure

B Ring (Schatzki Ring)

• Located precisely at the gastroesophageal mucosal junction (squamocolumnar junction) where squamous esophageal epithelium transitions to gastric columnar mucosa 1
• Represents the most clinically relevant esophageal ring, occurring in 6-14% of barium swallow examinations 1
• Found only in patients with cephalad displacement of the esophagogastric junction (hiatal hernia) and appears as a sharply circumferentially marginated transition 3

A Ring (Muscular Ring)

• Positioned at the junction between the tubular esophagus and the esophageal vestibule, approximately 2 cm proximal to the B ring 2
• Identified in only about 5% of videofluoroscopic esophagrams, making it a relatively uncommon finding 2
• Represents a muscular contraction rather than a fixed mucosal structure 2

Clinical Significance

B Ring Pathophysiology

• Dysphagia follows "Schatzki's rule": symptoms are usual with ring diameters ≤13 mm, rarely occur if diameter exceeds 20 mm, with a "grey area" between 13-20 mm 1
• Most common cause of intermittent dysphagia for solids and food bolus obstruction 1
• Associated with gastroesophageal reflux disease (GERD) and eosinophilic esophagitis 1
• Postulated to develop from mucosal infolding at the esophagogastric junction during esophageal shortening, with subsequent fibrosis creating a fixed organic diaphragm 3

A Ring Pathophysiology

• Associated with more severe gastroesophageal reflux, with mean DeMeester pH scores of 48.9 in patients with A rings versus 15.4 in controls 2
• Patients with A rings demonstrate significantly higher total percentage of time with pH < 4 (26.4% versus 7.7%) 2
• 70% of patients with A rings have erosive esophagitis compared to only 10% without A rings 2
• May represent either a compensatory mechanism to protect against reflux or an inflammatory consequence of peptic esophagitis 2

Diagnostic Detection

Optimal Imaging Techniques

• Biphasic esophagram is superior to endoscopy for detecting lower esophageal rings, with 95% detection rate compared to 76% for endoscopy 4
• Prone single-contrast views with continuous drinking of low-density barium are 2-3 times more likely to detect lower esophageal rings than upright double-contrast views due to better distal esophageal distention 4
• B rings may not be visible during endoscopy unless the gastroesophageal junction is adequately distended by air insufflation 1

Critical Diagnostic Pitfall

• Always exclude eosinophilic esophagitis by obtaining distal, mid, and proximal esophageal biopsies in symptomatic patients, as circular rings in eosinophilic esophagitis can mimic Schatzki rings 1, 5
• Look for additional endoscopic features including longitudinal furrowing, whitish exudates, edema, narrow-caliber esophagus, and "crêpe paper" mucosa 5
• 30% of eosinophilic esophagitis cases have normal-appearing mucosa endoscopically, making biopsies essential 5