AJR 2003; 180:745-747
© American Roentgen Ray Society
Overlap Phenomenon: A Potential Pitfall in the Radiographic Detection of Lower Esophageal Rings
Wendy C. Hsu1,
Marc S. Levine and
Stephen E. Rubesin
1 All authors: Department of Radiology, Hospital of the University of
Pennsylvania, 3400 Spruce St., Philadelphia, PA 19104.
Received June 7, 2002;
accepted after revision August 20, 2002.
Address correspondence to M. S. Levine.
Introduction
Lower esophageal rings are believed to be the most common cause of
dysphagia for solids in adults
[1]. Symptomatic lower
esophageal rings (also known as Schatzki's rings) typically appear as smooth,
symmetric ringlike constrictions at the gastroesophageal junction above a
hiatal hernia
[1,2,3].
Rings smaller than 13 mm in diameter almost always cause dysphagia, whereas
rings 13 mm or greater in diameter may or may not cause dysphagia, depending
on the eating habits of the patient
[1].
Lower esophageal rings are best detected on esophagography during
continuous drinking of a low-density barium suspension with the patient in a
prone, right anterior oblique position, a technique that maximizes distention
of the distal esophagus [4]. In
fact, a substantial number of symptomatic rings can be missed on
double-contrast esophagograms when images are obtained only with the patient
in an upright, left posterior oblique position because the distal esophagus is
inadequately distended [5,
6]. To obtain optimal detection
of these rings, investigators have stressed the importance of performing a
biphasic examination that includes routine prone, right anterior oblique
images of the esophagus obtained after administration of a low-density barium
suspension in all patients with dysphagia
[3,4,5,6].
However, we have become aware of another potential pitfall in the radiographic
diagnosis of lower esophageal rings on prone esophagograms: overlap of the
distal end of the esophagus and proximal end of a hiatal hernia in some
patients. We present a brief description of this overlap phenomenon and
discuss its implications.
Overlap Phenomenon
When patients with lower esophageal rings continuously ingest a low-density
barium suspension in the prone, right anterior oblique position, distention of
the distal esophagus and the adjacent hiatal hernia beyond the caliber of the
ring permits visualization of the ring in profile as a smooth, symmetric,
ringlike constriction at the gastroesophageal junction
[1,2,3].
However, the actual junction between the esophagus and the stomach (i.e., the
gastric cardia) is not always located at the apex of the hernia but, rather,
more caudally. As a result, the distal end of the esophagus may overlap the
proximal end of the hernia on fluoroscopy, obscuring the gastroesophageal
junction and preventing visualization of the ring.
The overlap occurs when the distended esophagus and adjacent hiatal hernia
are obliquely oriented to the viewing plane. This phenomenon sometimes can be
recognized by the presence of a double density with two superimposed, convex
collections of barium caused by overlap of the distal end of the esophagus
above the ring and the proximal end of the hernia below the ring (Figs.
1A and
2A). In such cases, additional
images obtained with the patient in a prone, right anterior oblique position
when overlap between the distal esophagus and adjacent hiatal hernia is no
longer present may permit visualization of these anatomic structures in
profile, enabling detection of lower esophageal rings previously obscured by
this phenomenon (Figs. 1B and
2B).
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Fig. 1A. —Overlap phenomenon obscuring symptomatic lower esophageal
ring in 73-year-old woman with dysphagia. Initial spot-image esophagogram of
distal esophagus obtained during continuous drinking of low-density barium
suspension by patient in prone, right anterior oblique position shows hiatal
hernia without evidence of lower esophageal ring. However, note double density
with two superimposed, convex collections of barium, caused by overlap of
distal end of esophagus (solid arrows) and proximal end of hernia
(open arrows).
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Fig. 2A. —Overlap phenomenon obscuring symptomatic lower esophageal
ring in 63-year-old woman with intermittent dysphagia. Initial spot-image
esophagogram of distal esophagus obtained during continuous drinking of
low-density barium suspension by patient in prone, right anterior oblique
position shows small hiatal hernia with two superimposed, convex collections
of barium caused by overlap of distal end of esophagus (solid arrows)
and proximal end of hernia (open arrows). Note similarity to findings
in Figure 1A.
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Fig. 1B. —Overlap phenomenon obscuring symptomatic lower esophageal
ring in 73-year-old woman with dysphagia. Esophagogram obtained during same
examination as A with patient in same position clearly shows marked
lower esophageal ring (arrow) when distal esophagus and adjacent
hiatal hernia no longer overlap. Note less distention of hernia than is seen
on A.
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Fig. 2B. —Overlap phenomenon obscuring symptomatic lower esophageal
ring in 63-year-old woman with intermittent dysphagia. Esophagogram obtained
during same examination as A with patient in same position shows mild
lower esophageal ring (arrows) when distal esophagus and adjacent
hiatal hernia no longer overlap. Note less distention of hernia than is seen
on A.
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Discussion
When barium studies are performed on patients with lower esophageal rings,
the esophagus above the ring and hiatal hernia below the ring must be
distended beyond the caliber of the ring itself to adequately visualize these
structures. For this reason, investigators have emphasized the importance of
obtaining a biphasic examination that includes right anterior oblique views of
the esophagus obtained with the patient in a prone position during continuous
drinking of a low-density barium suspension to improve detection of lower
esophageal rings by optimizing distention of the distal esophagus
[3,4,5,6].
In some patients, overdistention of the hiatal hernia paradoxically results in
overlap of the distal end of the esophagus and proximal end of the hernia,
producing a double density of two superimposed, convex collections of barium
that obscure the region of the gastroesophageal junction and limit
visualization of the ring (Figs.
1A and
2A). This overlap phenomenon
represents a potential pitfall that can prevent detection of even high-grade
rings. Therefore, to avoid missing lower esophageal rings on prone
esophagograms, it is important for radiologists to recognize the double
density produced by this phenomenon.
When overlap between the distal esophagus and an adjacent hiatal hernia is
observed, additional images of the distal esophagus should be obtained with
the patient in the prone, right anterior oblique position to visualize the
gastroesophageal junction with minimal or no overlap of these structures. The
anatomy of this region can then be viewed in profile, enabling detection of
lower esophageal rings and determination of their size (Figs.
1B and
2B). In our experience, the
overlap can be eliminated in some cases by placing a bolster beneath the
patient, by rotating the patient slightly, or by having the patient drink the
low-density barium suspension intermittently so that images can be obtained
when the hiatal hernia is less distended. If remote control fluoroscopy units
are available, images of the gastroesophageal junction could also be obtained
with the beam angled toward the feet to minimize overlap at the
gastroesophageal junction and improve detection of these rings.
When lower esophageal rings are detected on barium studies, a barium tablet
12 mm in diameter can be administered to the patient to objectively quantify
the caliber of the ring (i.e., the barium tablet will lodge above rings <
12 mm in diameter). Alternatively, the patient can be asked to swallow a
barium-impregnated marshmallow bolus to determine whether the bolus becomes
impacted above the ring and, if it does, whether this impaction reproduces the
patient's dysphagia [7].
In conclusion, radiologists should be aware that overlap of the distal
esophagus and an adjacent hiatal hernia may obscure the region of the
gastroesophageal junction on esophagography performed with the patient in the
prone position, preventing visualization of lower esophageal rings. When this
phenomenon occurs, additional images of the gastroesophageal junction should
be obtained when minimal or no overlap of the distal esophagus and adjacent
hiatal hernia is present, which will improve detection of these rings.
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Introduction
Overlap Phenomenon
