Lower esophageal mucosal rings
What is the relationship of lower esophageal mucosal rings to lower esophageal sphincter pressure, abnormal gastroesophageal reflux, and hiatal hernias?
M.Y.M. Chen, D.J.Ott (Winston-Salem)
The lower esophageal mucosal ring (LEMR) is an acquired thin membrane that demarcates the esophagogastric junction, and a criterion used to diagnose hiatal hernia (Figure 1). Although the etiology of LEMR is not clear, reflux esophagitis has been proposed as a potential cause. Abnormal gastroesophageal reflux (GER) and reflux esophagitis have a multifactorial pathogenesis. However, lower esophageal sphincter dysfunction is an important cause, seen as transient or prolonged episodes of hypotension of the lower esophageal sphincter (LES) pressure. The correlation between LEMR and LES pressure, abnormal gastroesophageal reflux, and hiatal hernia is reviewed.
Correlation of LEMR and LES pressure
The lower esophageal sphincter is a high-pressure zone approximately 2-4 cm long located in the esophagogastric region. It is believed to be the major component regulating the function of the antireflux barrier. Measurement of LES pressure and its response to swallowing assesses the function of the lower esophageal sphincter and antireflux barrier. The resting LES pressure in a patient with abnormal GER is often lower than that of a normal person. Patients with persistent low LES pressure are likely to have more GER, whereas those with normal LES pressure may have less reflux. Some patients with intermittent episodes of reflux and transient sphincter dysfunction may maintain a normal resting LES pressure. Although the pathogenesis of gastroesophageal reflux disease is multifactorial, the low LES pressure may be a causative factor, and reflux esophagitis is a potential cause of LEMR.
In general, the mean LES pressure in patients with LEMR is lower than in those without LEMR [1, 2]. Eckardt et al.  found that the LES pressure was 21.2 ± 2.7 mmHg in 12 asymptomatic patients with LEMR but was 26.1 ± 4.1 mmHg in the control subjects . Another investigation  showed that LES pressure in patients with LEMR was similar to that in a normal control group, but in a subgroup of patients with LEMR associated with esophagitis, LES pressure (9.2 ± 3.8 mmHg) was significantly lower than in a control group (14.7 ± 5.6 mmHg). In a third study , the mean LES pressure in patients with LEMR was 23.8 mmHg (range, 4.2-64.0 mmHg), whereas the mean LES pressure in patients without LEMR was 28.7 mmHg (range, 8.0-59.0 mmHg) . In all three studies, patients with LEMR had a lower mean LES pressure than did those without LEMR, but the difference was not significant statistically. These results do not support a direct relationship between LEMR and prolonged lower esophageal sphincter hypotension.
The diameter of LEMR was also correlated with LES pressure . Patients with mucosal rings 13 mm or less (Figure 2) in caliber had a lower mean LES pressure (20 mmHg) than did patients with LEMR (28 mmHg) of wider diameter; however, no statistically significant difference was found. This observation further supports the finding that if LEMR is related to reflux esophagitis, other factors may be more important in the pathogenesis of LEMR than prolonged lower esophageal sphincter hypotension.
Figure 1. Barium esophagram shows a typical lower esophageal mucosal ring (arrowheads) demarcating the esophageal vestibule (V) and a hiatal hernia (HH).
Figure 2. Patient with dysphagia for solid food. Barium esophagram shows a mucosal ring (arrow) measuring only 6 mm in caliber.
The relationship of LEMR and esophageal body function measured by manometry has also been addressed . The mean amplitude of primary peristaltic contractions in patients with LEMR (70 ± 38 mmHg) was not significantly different from that of the control group (79 ± 29 mmHg). In another study , the similarity of these results was confirmed; esophageal amplitude was 95.3 ± 49.2 mmHg in patients with LEMR, whereas amplitude was 94.9 ± 45.2 mmHg in the control group. These data suggest that the presence of LEMR has no relationship to esophageal motility, as measured by the duration and amplitude of esophageal primary peristalsis [1, 3]. The presence of LEMR did not affect the spectrum of abnormal esophageal motility disorders.
LEMR and abnormal gastroesophageal reflux
The evidence for a relationship between LEMR and abnormal GER also remains controversial. The mucosal ring is believed to be an acquired lesion and possibly related to reflux esophagitis (Figures 3 and 4). This concept is supported by the observation of occasional progression of an LEMR to a typical peptic stricture with the presence of reflux esophagitis . Since the LEMR may be a part of the spectrum of peptic stricture, more severe reflux disease, abnormal pH monitoring, and lower LES pressure would be expected in patients with LEMR.
Figure 3. Barium reflux from the stomach into the lower esophagus. A mucosal ring (arrow) and hiatal hernia (hh) are also present.
Figure 4. Full-column (A) and mucosal relief (B) views show a broad mucosal ring and a hiatal hernia (hh) associated with thickened and irregular esophageal mucosal folds. A reflux esophagitis was confirmed by endoscopy.
In patients with LEMR, the prevalence of abnormal GER is higher than in control patients. In one recent study , 31% of patients with LEMR had abnormal pH findings (pH < 4), compared to 17% of patients without mucosal rings who had abnormal pH results. In another study , 65% of patients with LEMR had abnormal GER and in most of them, endoscopy showed erosive esophagitis in the lower esophagus.
The presence of a LEMR is believed to have a potential role in the prevention of reflux episodes in patients with hiatal hernia. Jamieson et al.  showed that patients with LEMR had a lower prevalence of reflux episodes as detected by 24-hour esophageal pH monitoring and had milder symptoms than did patients with hiatal hernia only.
The correlation between the caliber of the mucosal ring and episodes of GER has been also assessed. Patients with wider mucosal rings may have fewer episodes of abnormal gastroesophageal reflux. Ott et al.  found that 40% of patients with mucosal rings less than 20 mm in caliber had abnormal GER , whereas 28% of patients with wider mucosal rings had reflux; however, the difference was not statistically significant. Therefore, neither the presence nor the size of LEMR contributes to a higher percentage of abnormal reflux in patients with hiatal hernia.
Lower esophageal mucosal ring and hiatal hernia
The LEMR is located at the esophagogastric junction and the squamocolumnar epithelial line, and is a criterion for the diagnosis of hiatal hernia. Therefore, the effect of hiatal hernia and LEMR on lower esophageal sphincter function and possible reflux esophagitis might be similar.
Hiatal hernia is a common but non specific radiographic and endoscopic finding in patients with gastroesophageal reflux disease. The reported prevalence of hiatal hernia in the radiologic adult population has been 40%-60% , and the prevalence increases with age. Many patients with a hiatal hernia do not have gastroesophageal reflux disease; however, about 90% of patients with reflux esophagitis shown endoscopically have a hiatal hernia .
Patients with a hiatal hernia have lower LES pressure. A significantly lower LES pressure (12 ± 6 mmHg) was reported in patients with endoscopically diagnosed hiatal hernia, patulous hiatus, or a combination than in patients with neither diagnosis, who had a normal LES pressure (22 ± 15 mmHg) . However, hiatal hernia demonstrated radiographically was not significantly associated with reduced LES pressure . The major difference between these two conflicting studies was in the use of endoscopic or radiographic modalities to diagnose hiatal hernia. Small hiatal hernias (< 2 cm) that are demonstrated radiographically may not be seen at endoscopy; therefore, patients with hiatal hernia shown radiographically had a lower prevalence of associated reflux esophagitis than did patients whose hiatal hernia was diagnosed with endoscopy. In patients with a hiatal hernia, with or without an associated mucosal ring, LES pressure may be lower than in the normal group, but the difference appears not to be significant.
The frequency of GER is higher in patients with either hiatal hernia only or hiatal hernia with associated mucosal ring than in the normal population. In one study , about 33% of patients with hiatal hernia had abnormal GER; similarly, 31% of patients with associated mucosal ring had abnormal GER. Both hiatal hernia and LEMR were poor predictors of the presence of abnormal gastroesophageal reflux.
In summary, the LEMR is located at the esophagogastric junction and is one criterion for the diagnosis of the hiatal hernia. The relationship of LEMR and hiatal hernia suggests that both would have similar effects on lower esophageal sphincter function as reflected by the lower esophageal sphincter pressure and episodes of abnormal gastroesophageal reflux. Patients with LEMR have lower LES pressure and a higher prevalence of gastroesophageal reflux; however, the differences are similar to patients with hiatal hernia alone.