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731
Diagnosis on Supine
Marc S. Levin& Jac D. Schemer Stephen E. Rubesin Inor Laufer HansHerIiner
A blinded, abdominal
of Pneumoperitoneum Abdominal Radiographs
retrospective
radiographs
study was performed
in diagnosing
to determine
pneumoperitoneum.
the value
Supine
of supine
films from
44 cases
of pneumopenitoneum were randomly interspersed among supine films from 87 control subjects without free air, and the films were reviewed for the presence or absence of various signs of pneumoperitoneum, including Rigler’s sign (gas on both sides of the
bowel wall), the falciform ligament sign (gas outlining the falciform ligament), the football sign (gas outlining the pentoneal cavity), the inverted-V sign (gas outlining the medial umbilical folds), and the right-upper-quadrant gas sign (localized gas in the right upper quadrant). One or more of these signs were present in 26 cases (59%) of pneumoperitoneum, including the right-upper-quadrant gas sign in 18 cases (41%), Rigler’s sign in 14 cases
(32%),
Unfortunately,
and there
the were
falciform frequent
ligament errors
and
football
in the interpretation
signs
in one
case
each
(2%).
of the right-upper-quadrant
gas sign and Rigler’s sign, with a total of I 1 false-positive cases (13%). Further analysis of the true-positive right-upper-quadrant gas signs showed that these gas collections were always triangular or linear with an inferolateral to superomedial orientation and, if triangular, a concave superolateral border. In the true-positive Rigler’s signs, the bowel wall thickness ranged from 1 to 8 mm, whereas the false positives all had a bowel wall thickness of 1 mm or less. Proper interpretation of the various signs of pneumopentoneum on supine films should lead to more accurate diagnosis of this condition. AJR
156:731-735,
April 1991
Since the early 1 900s, upright or left lateral decubitus films of the abdomen have been recognized as a valuable aid for the diagnosis of pneumoperitoneum [1 2]. In clinical practice, however, many patients with an acute abdomen are too sick or ,
Received September 10, 1990; accepted after revision October 23, 1990. 1 All authors: Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia, PA 19104. Address to M. S. Levine. 0361-803X/91/1564-0731 0 American Roentgen
Ray Society
3400 Spruce St., reprint requests
debilitated to stand or lie on their side, so that supine abdominal radiographs may be the only films obtained. Various signs of pneumoperitoneum that have been described on supine films include Rigler’s sign (visualization of both sides of the bowel wall) [3], the falciform ligament sign (visualization of the falciform ligament as a thin, linear density in the right upper quadrant), the football sign (visualization ofthe peritoneal cavity as an oval gas shadow) [4], the inverted-V sign (visualization of the medial umbilical folds in the pelvis) [5, 6], and the right-upper-quadrant gas sign (visualization of localized extraluminal gas collections in the right upper quadrant) [7-9]. Nevertheless, many authors believe that supine abdominal radiographs have limited value in diagnosing pneumoperitoneum [1 0-1 2]. This study was undertaken to determine the value of supine films in these patients.
Materials Inpatient
and Methods radiology
log
sheets
at our
hospital
were
used
to identify
pentoneum diagnosed on upright or left lateral decubitus films of supine abdominal radiographs also had been obtained. No portable
44 the
cases abdomen
abdominal
of pneumoin which
radiographs
732
LEVINE
were included in this study. The 44 supine films were randomly interspersed among supine films from 87 other control cases in which there was no evidence of pneumoperitoneum on upright or decubitus films.
Each of those 1 31 supine films were then reviewed by an experigastrointestinal radiologist who had no knowledge of the findings on upright or decubitus films. The supine films were evaluated for the presence or absence of five previously described signs of pneumoperitoneum, including Rigler’s sign, the falciform ligament sign, the football sign, the inverted-V sign, and the right-upperquadrant gas sign. Subsequently, the films were analyzed to determine the location and thickness of the bowel wall in all patients with Rigler’s sign and the size, shape, and location of the gas collections
Downloaded from www.ajronline.org by 85.202.194.212 on 01/23/19 from IP address 85.202.194.212. Copyright ARRS. For personal use only; all rights reserved
enced
in all patients
with
the
right-upper-quadrant
gas
The amount of free intrapentoneal
air
sign.
in the
44 cases
of pneumo-
pentoneum was also quantified by measuring the vertical distance from the apex of the diaphragm to the liver on upright films or from the right lateral wall of the abdomen to the liver on decubitus films. The presence or absence of these various signs of pneumoperitoneum on supine films was then correlated with the amount of free air on upright or decubitus films.
are summarized
in Table
1.
Gas Sign
quadrant
The 13 triangular
superolateral
border,
collections
and their
mean
all had a concave
longest
dimension
3.2 cm (range, 2-7 cm). The five linear collections
was
had a mean
length of 4.0 cm (range, 2-5 cm). At the same time, false-positive right-upper-quadrant gas signs (five triangular and one linear) were present in six (7%) of 87 patients who had no evidence of pneumopentoneum on upright or left lateral decubitus films (Fig. 2). Of the five falsepositive triangular collections, three had a convex superolat-
Rig/er’s
1: Summary
Pneumopentoneum
of Radiographic and 87 Controls
Findings
of
in 44 Cases
stomach
Right-upper-quadrant
Triangular Linear
Total Rigler’s Falciform Football
ligament
InvertedV
One or more
True Positive
Cases
%
False Positive
Sensitivity
was
involved
in three,
the small
bowel
in two,
the
and the in those
14 cases was 5.8 mm (range, 4-8 mm) for the stomach, 1.8 mm (range, 1 -2 mm) for the small bowel, and 1 .1 mm (range,
(range,
0.5-1
Rigler’s
.0 mm).
In all five
sign, the apparent
patients
with
wall thickness
a false-
therefore
was 1 mm or less.
One patient had a variant of Rigler’s sign in which gas was seen only outside the wall of several fluid-filled loops of dilated small
bowel,
producing
a distinctive
radiologic
appearance
(Fig. 5). Other
Signs
The falciform ligament sign (Fig. 6) and football sign (Fig. 3A) were each present on supine films in only one of 44 cases (2%) of pneumoperitoneum. These cases had a positive rightupper-quadrant gas sign (Fig. 6) or Rigler’s sign (Fig. 3A), so that pneumoperitoneum would have been diagnosed even in the absence of these findings. Finally, the inverted-V sign was not present on supine films in any cases of pneumoperitoneum. of Free Intraperitonea/
Air
of
distance
decubitus
films
was
between
the diaphragm
and liver or the
wall and liver on upright 1 .9 cm (range,
cases of pneumoperitoneum
0.1-5.0
or left lateral cm)
that were diagnosed
in the 26
on supine
films but only 0.6 cm (range, 0.1 -1 .2 cm) in the 1 8 cases of pneumoperitoneum that were not diagnosed on these films.
gas
13 5
5 1
30 11
18
6
41
14 1 1
5 0 0
32 2 2
0
0 10
0 59
26
represented
colon in five, the small bowel and colon in three, stomach and colon in one. The mean wall thickness
right lateral abdominal
.
Sign
probably
Rigler’s sign was present on supine films in 14 (32%) of 44 cases of pneumoperitoneum (Fig. 3). Of these 14 cases in which gas was seen on both sides of the bowel wall, the
The mean
No.
into the lateral half of the right upper
Sign
Amount TABLE
also extended
quadrant (Fig. 2C) and, in retrospect, fat in the subhepatic space.
positive
The right-upper-quadrant gas sign was present on supine films in 1 8 (41 %) of 44 cases of pneumoperitoneum (Fig. 1). Thirteen (30%) had a triangular gas collection (Fig. 1A) and five (1 1%) had a linear gas collection (Fig. 1 B) in the right upper quadrant. Whether triangular or linear, these 18 gas collections all had an inferolateral to superomedial orientation, and all were located in the medial half of the right upper
quadrant.
1991
eral border (Fig. 2A), one had an inferomedial to superolateral orientation (Fig. 2B), and one was located in the lateral half of the right upper quadrant. In retrospect, most of these collections probably represented gas in the duodenal bulb. The one false-positive linear gas collection in the right upper
mm Right-Upper-Quadrant
AJR:156,Apnl
1-2 mm) for the colon. In all 1 4 patients with a true-positive Rigler’s sign, the wall thickness therefore was 1 mm or greater. Of the five false-positive cases (6%) of Rigler’s sign, the small bowel was involved in two and the colon in three (Fig. 4). The mean wall thickness in those five cases was 0.6
Results
The results
ET AL.
Thus, a greater amount in patients on supine
of free intrapentoneal
who had one or more abdominal radiographs.
signs
air was present
of pneumoperitoneum
Discussion
Unless a considerable amount of free air is present in the abdomen, supine abdominal radiographs are generally
Downloaded from www.ajronline.org by 85.202.194.212 on 01/23/19 from IP address 85.202.194.212. Copyright ARRS. For personal use only; all rights reserved
AJR:156,
April1991
PNEUMOPERITONEUM
ON
SUPINE
ABDOMINAL
FILMS
733
Fig. 1.-Right-upper-quadrant gas sign on radiographs in two patients with pneumoperitoneum. A, Triangular lucency (arrow) with inferolateral to superomedial orientation and concave superolateral border. Also note medial location of gas adjacent to lower thoracic spine. B, Linear lucency (arrow) in subhepatic region. Again note inferolateral to superomedial orientation of gas.
B
A
Fig. 2.-False-positive A, B, C, Note
right-upper-quadrant gas sign on radiographs in three patients without pneumoperitoneum. Triangular lucency (arrow) with convex superolateral border. In retrospect, this probably represents gas in duodenal bulb. Triangular lucency (arrows) with inferomedial to superolateral orientation. In retrospect, this also may be gas in duodenal bulb. Linear lucency (straight arrows) extending into lateral half of right upper quadrant. In retrospect, this probably represents fat in subhepatic skin fold (curved arrows) more inferioriy.
space.
.“
.,..
Fig. 3.-Rigler’s sign on radiographs tient with pneumoperitoneum.
:
in pa-
A, Close-up
view of left upper quadrant shows both sides of gastric wall (straight white arrows), which appears quite thick. This patient also has football sign (straight black arrows) of pneumoperitoneum. Gastrostomy tube (curved arrow) is present in stomach. B, Close-up view of right lower quadrant shows gas outiining both sides of cecal wall (arrows), which is several millimeters thick.
gas outlining
L A
B
.ir’
LEVINE
734
thought to have limited value in diagnosing pneumoperitoneum [10-12]. Our study confirmed that patients with smaller amounts of free air are less likely to have radiologic evidence of pneumoperitoneum on supine films. Nevertheless, one or
Downloaded from www.ajronline.org by 85.202.194.212 on 01/23/19 from IP address 85.202.194.212. Copyright ARRS. For personal use only; all rights reserved
more signs of pneumoperitoneum in 59% of cases. Because life-threatening situation,
these various this condition.
were present on these films
pneumoperitoneum radiologists need
signs and of their relative
may indicate
a
to be aware of value in diagnosing
In our study, the most frequent sign of pneumoperitoneum on supine abdominal radiographs was the right-upper-quadrant gas sign, which was present in 41 % of cases (Fig. 1). Surprisingly, this important sign of pneumoperitoneum has received little attention in the radiologic literature [7-9]. In a retrospective study by Menuck and Siemers [8], localized right-upper-quadrant gas collections were present on supine films in 49% of patients with pneumoperitoneum, whereas the more well-known signs of pneumoperitoneum (i.e., Rigler’s sign and the falciform ligament sign) were present in only
1 7% of patients.
In our study
and that
by Menuck
and
ET AL.
AJR:156,
April 1991
Siemers, these gas collections appeared as obliquely onented, triangular or linear lucencies in the right upper quadrant. It has been postulated that the linear collections represent gas in the right subhepatic space, whereas the triangular collections represent gas in the posterior recess of the right subhepatic space, also known as the hepatorenal fossa or Monison pouch [7-9]. Further analysis of our patients revealed that all of the truepositive right-upper-quadrant gas collections were located in the medial half of the right upper quadrant with an inferolateral to superomedial orientation, and, if triangular, with a concave superolateral border (Fig. 1). In contrast, all of the falsepositive right-upper-quadrant collections had a convex superolateral border or an inferomedial to superolateral orientation or were located in the lateral half of the right upper quadrant (Fig. 2). Thus, if properly interpreted, the right-upper-quadrant
gas sign is probably
the single best sign of pneumopenitoneum
on supine films. The second most frequent sign of pneumopenitoneum on supine abdominal radiographs was Riglen’s sign, which was present in 32% of cases (Fig. 3). However, a false-positive Rigler’s sign was present in five cases (6%) in which there was no evidence of pneumopenitoneum on upright or left lateral decubitus films (Fig. 4). These false-positive findings may have resulted from Mach bands, a phenomenon in which there is the perception of a line at the interface of two regions
of differing densities [1 3]. This problem is more likely to occur when two bowel loops are overlapping, so that the edge of one bowel wall is superimposed on the gas-filled lumen of another loop. However, all of the false-positive cases had an apparent wall thickness of 1 mm or less (Fig. 4), whereas all of the true positives had a wall thickness of 1 mm or greater
(Fig. 3). Thus, evaluation
Fig. 4.-False-positive Rigler’s sign on radiograph in patient without pneumopenltoneum. Note how line (arrows) along margin of bowel has no discernible thickness in this case.
of wall thickness
is a useful criterion
for differentiating Mach bandsfrom true-positive Rigler’s signs in patients with pneumoperitoneum. Furthermore, there were no false-positive cases with gas on both sides of the wall of the stomach, so that the latter finding should be considered a particularly reliable sign of pneumopenitoneum (Fig. 3A). Interestingly, one patient had a variant of Rigler’s sign in which air was only seen outside the wall of several fluid-filled loops of dilated small bowel (Fig. 5). Fig. 5.-Variant pneumoperitoneum.
of Rigler’s sign in patient with Radiograph shows unusually sharp, well-defined outer border (arrow. heads) of several fluid-filled loops of dilated small bowel caused by gas In peritoneal cavity.
Fig.
6.-Falciform
ligament
sign
and
right-
upper-quadrant
gas sign in patient with pneumopenitoneum. Thin, linear, soft-tissue density (black arrow) in right upper quadrant is due to gas outlining falciform ligament. More lateral hiangular
lucency
subhepatic region.
(white
arrow)
is due to gas in
AJR:156,
PNEUMOPERITONEUM
April 1991
Other well-known
signs of pneumoperitoneum
Downloaded from www.ajronline.org by 85.202.194.212 on 01/23/19 from IP address 85.202.194.212. Copyright ARRS. For personal use only; all rights reserved
films, such as the falciform inverted-V sign, were each
ON SUPINE
on supine
ligament sign, football sign, and present in less than 3% of cases
and were always seen in patients who had a positive Rigler’s sign (Fig. 3A) or right-upper-quadrant gas sign (Fig. 6). Thus, for all practical purposes, pneumoperitoneum is primarily diagnosed on supine films by the presence of gas on both sides of the bowel
wall or by triangular
or linear
gas collections
in
the right upper quadrant. Proper interpretation of these signs should lead to more accurate diagnosis of this condition.
REFERENCES 1 . Vaughn RT, Brams WA. Early recognition
of acute perforation of gastric and duodenal ulcer by x-ray examination of spontaneous pneumoperitoneum. Surg Gynecol Obstet 1924;39:610-617 2. Miller RE, Nelson SW. The roentgenologic demonstration of tiny amounts of free intraperitoneal 1971;1 12:574-585
gas:
experimental
and
clinical
studies.
AJR
ABDOMINAL
FILMS
735
3. Rigler LG. Spontaneous pneumoperitoneum: a roentgenologic sign found in the supine position. Radiology 1941;37:604-607 4. Miller RE. Perforated viscus in infants: a new roentgen sign. Radiology 1960;74:65-67 5. Weiner Cl, Diaconis JN, Dennis JM. The Inverted V’: a new sign of pneumoperitoneum.
Radiology
1973;107:47-48
6. Bray JF. The Inverted V sign of pneumoperitoneum. Radiology 1984;151 :45-46 7. Hajdu N, de Lacey G. The Rutherford Monson pouch: a characteristic appearance on abdominal radiographs. Br J Radiol 1970;43:706-709 8. Menuck L, Siemers PT. Pneumoperitoneum: importance of right upper quadrant features. AiR 1976;127:753-756 9. BrilI PW, Olson SR, Winchester P. Neonatal necrotizing enterocolitis: air in Monson pouch. Radiology 1990;174:469-471 10. Berdon WE, Baker DH, Leonidas J. Advantages of prone positioning in gastrointestinal and gastrourological roentgenologic studies in infants and children. AJR 1968;103:444-445. 1 1 . Hamed AK. Diagnosis of pneumoperitoneum in the adult. Nebr Med J 1974;59: 185-191 12. Markowitz 5K, Ziter FM. The lateral chest film and pneumoperitoneum. Mn Emerg Med 1986;15:425-427 13. Edholm P. Boundaries in the radiographic image. I. General principles for perception of boundaries and their application to the image. Acta Radiol 1981;22:457-473
731
Diagnosis on Supine
Marc S. Levin& Jac D. Schemer Stephen E. Rubesin Inor Laufer HansHerIiner
A blinded, abdominal
of Pneumoperitoneum Abdominal Radiographs
retrospective
radiographs
study was performed
in diagnosing
to determine
pneumoperitoneum.
the value
Supine
of supine
films from
44 cases
of pneumopenitoneum were randomly interspersed among supine films from 87 control subjects without free air, and the films were reviewed for the presence or absence of various signs of pneumoperitoneum, including Rigler’s sign (gas on both sides of the
bowel wall), the falciform ligament sign (gas outlining the falciform ligament), the football sign (gas outlining the pentoneal cavity), the inverted-V sign (gas outlining the medial umbilical folds), and the right-upper-quadrant gas sign (localized gas in the right upper quadrant). One or more of these signs were present in 26 cases (59%) of pneumoperitoneum, including the right-upper-quadrant gas sign in 18 cases (41%), Rigler’s sign in 14 cases
(32%),
Unfortunately,
and there
the were
falciform frequent
ligament errors
and
football
in the interpretation
signs
in one
case
each
(2%).
of the right-upper-quadrant
gas sign and Rigler’s sign, with a total of I 1 false-positive cases (13%). Further analysis of the true-positive right-upper-quadrant gas signs showed that these gas collections were always triangular or linear with an inferolateral to superomedial orientation and, if triangular, a concave superolateral border. In the true-positive Rigler’s signs, the bowel wall thickness ranged from 1 to 8 mm, whereas the false positives all had a bowel wall thickness of 1 mm or less. Proper interpretation of the various signs of pneumopentoneum on supine films should lead to more accurate diagnosis of this condition. AJR
156:731-735,
April 1991
Since the early 1 900s, upright or left lateral decubitus films of the abdomen have been recognized as a valuable aid for the diagnosis of pneumoperitoneum [1 2]. In clinical practice, however, many patients with an acute abdomen are too sick or ,
Received September 10, 1990; accepted after revision October 23, 1990. 1 All authors: Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia, PA 19104. Address to M. S. Levine. 0361-803X/91/1564-0731 0 American Roentgen
Ray Society
3400 Spruce St., reprint requests
debilitated to stand or lie on their side, so that supine abdominal radiographs may be the only films obtained. Various signs of pneumoperitoneum that have been described on supine films include Rigler’s sign (visualization of both sides of the bowel wall) [3], the falciform ligament sign (visualization of the falciform ligament as a thin, linear density in the right upper quadrant), the football sign (visualization ofthe peritoneal cavity as an oval gas shadow) [4], the inverted-V sign (visualization of the medial umbilical folds in the pelvis) [5, 6], and the right-upper-quadrant gas sign (visualization of localized extraluminal gas collections in the right upper quadrant) [7-9]. Nevertheless, many authors believe that supine abdominal radiographs have limited value in diagnosing pneumoperitoneum [1 0-1 2]. This study was undertaken to determine the value of supine films in these patients.
Materials Inpatient
and Methods radiology
log
sheets
at our
hospital
were
used
to identify
pentoneum diagnosed on upright or left lateral decubitus films of supine abdominal radiographs also had been obtained. No portable
44 the
cases abdomen
abdominal
of pneumoin which
radiographs
732
LEVINE
were included in this study. The 44 supine films were randomly interspersed among supine films from 87 other control cases in which there was no evidence of pneumoperitoneum on upright or decubitus films.
Each of those 1 31 supine films were then reviewed by an experigastrointestinal radiologist who had no knowledge of the findings on upright or decubitus films. The supine films were evaluated for the presence or absence of five previously described signs of pneumoperitoneum, including Rigler’s sign, the falciform ligament sign, the football sign, the inverted-V sign, and the right-upperquadrant gas sign. Subsequently, the films were analyzed to determine the location and thickness of the bowel wall in all patients with Rigler’s sign and the size, shape, and location of the gas collections
Downloaded from www.ajronline.org by 85.202.194.212 on 01/23/19 from IP address 85.202.194.212. Copyright ARRS. For personal use only; all rights reserved
enced
in all patients
with
the
right-upper-quadrant
gas
The amount of free intrapentoneal
air
sign.
in the
44 cases
of pneumo-
pentoneum was also quantified by measuring the vertical distance from the apex of the diaphragm to the liver on upright films or from the right lateral wall of the abdomen to the liver on decubitus films. The presence or absence of these various signs of pneumoperitoneum on supine films was then correlated with the amount of free air on upright or decubitus films.
are summarized
in Table
1.
Gas Sign
quadrant
The 13 triangular
superolateral
border,
collections
and their
mean
all had a concave
longest
dimension
3.2 cm (range, 2-7 cm). The five linear collections
was
had a mean
length of 4.0 cm (range, 2-5 cm). At the same time, false-positive right-upper-quadrant gas signs (five triangular and one linear) were present in six (7%) of 87 patients who had no evidence of pneumopentoneum on upright or left lateral decubitus films (Fig. 2). Of the five falsepositive triangular collections, three had a convex superolat-
Rig/er’s
1: Summary
Pneumopentoneum
of Radiographic and 87 Controls
Findings
of
in 44 Cases
stomach
Right-upper-quadrant
Triangular Linear
Total Rigler’s Falciform Football
ligament
InvertedV
One or more
True Positive
Cases
%
False Positive
Sensitivity
was
involved
in three,
the small
bowel
in two,
the
and the in those
14 cases was 5.8 mm (range, 4-8 mm) for the stomach, 1.8 mm (range, 1 -2 mm) for the small bowel, and 1 .1 mm (range,
(range,
0.5-1
Rigler’s
.0 mm).
In all five
sign, the apparent
patients
with
wall thickness
a false-
therefore
was 1 mm or less.
One patient had a variant of Rigler’s sign in which gas was seen only outside the wall of several fluid-filled loops of dilated small
bowel,
producing
a distinctive
radiologic
appearance
(Fig. 5). Other
Signs
The falciform ligament sign (Fig. 6) and football sign (Fig. 3A) were each present on supine films in only one of 44 cases (2%) of pneumoperitoneum. These cases had a positive rightupper-quadrant gas sign (Fig. 6) or Rigler’s sign (Fig. 3A), so that pneumoperitoneum would have been diagnosed even in the absence of these findings. Finally, the inverted-V sign was not present on supine films in any cases of pneumoperitoneum. of Free Intraperitonea/
Air
of
distance
decubitus
films
was
between
the diaphragm
and liver or the
wall and liver on upright 1 .9 cm (range,
cases of pneumoperitoneum
0.1-5.0
or left lateral cm)
that were diagnosed
in the 26
on supine
films but only 0.6 cm (range, 0.1 -1 .2 cm) in the 1 8 cases of pneumoperitoneum that were not diagnosed on these films.
gas
13 5
5 1
30 11
18
6
41
14 1 1
5 0 0
32 2 2
0
0 10
0 59
26
represented
colon in five, the small bowel and colon in three, stomach and colon in one. The mean wall thickness
right lateral abdominal
.
Sign
probably
Rigler’s sign was present on supine films in 14 (32%) of 44 cases of pneumoperitoneum (Fig. 3). Of these 14 cases in which gas was seen on both sides of the bowel wall, the
The mean
No.
into the lateral half of the right upper
Sign
Amount TABLE
also extended
quadrant (Fig. 2C) and, in retrospect, fat in the subhepatic space.
positive
The right-upper-quadrant gas sign was present on supine films in 1 8 (41 %) of 44 cases of pneumoperitoneum (Fig. 1). Thirteen (30%) had a triangular gas collection (Fig. 1A) and five (1 1%) had a linear gas collection (Fig. 1 B) in the right upper quadrant. Whether triangular or linear, these 18 gas collections all had an inferolateral to superomedial orientation, and all were located in the medial half of the right upper
quadrant.
1991
eral border (Fig. 2A), one had an inferomedial to superolateral orientation (Fig. 2B), and one was located in the lateral half of the right upper quadrant. In retrospect, most of these collections probably represented gas in the duodenal bulb. The one false-positive linear gas collection in the right upper
mm Right-Upper-Quadrant
AJR:156,Apnl
1-2 mm) for the colon. In all 1 4 patients with a true-positive Rigler’s sign, the wall thickness therefore was 1 mm or greater. Of the five false-positive cases (6%) of Rigler’s sign, the small bowel was involved in two and the colon in three (Fig. 4). The mean wall thickness in those five cases was 0.6
Results
The results
ET AL.
Thus, a greater amount in patients on supine
of free intrapentoneal
who had one or more abdominal radiographs.
signs
air was present
of pneumoperitoneum
Discussion
Unless a considerable amount of free air is present in the abdomen, supine abdominal radiographs are generally
Downloaded from www.ajronline.org by 85.202.194.212 on 01/23/19 from IP address 85.202.194.212. Copyright ARRS. For personal use only; all rights reserved
AJR:156,
April1991
PNEUMOPERITONEUM
ON
SUPINE
ABDOMINAL
FILMS
733
Fig. 1.-Right-upper-quadrant gas sign on radiographs in two patients with pneumoperitoneum. A, Triangular lucency (arrow) with inferolateral to superomedial orientation and concave superolateral border. Also note medial location of gas adjacent to lower thoracic spine. B, Linear lucency (arrow) in subhepatic region. Again note inferolateral to superomedial orientation of gas.
B
A
Fig. 2.-False-positive A, B, C, Note
right-upper-quadrant gas sign on radiographs in three patients without pneumoperitoneum. Triangular lucency (arrow) with convex superolateral border. In retrospect, this probably represents gas in duodenal bulb. Triangular lucency (arrows) with inferomedial to superolateral orientation. In retrospect, this also may be gas in duodenal bulb. Linear lucency (straight arrows) extending into lateral half of right upper quadrant. In retrospect, this probably represents fat in subhepatic skin fold (curved arrows) more inferioriy.
space.
.“
.,..
Fig. 3.-Rigler’s sign on radiographs tient with pneumoperitoneum.
:
in pa-
A, Close-up
view of left upper quadrant shows both sides of gastric wall (straight white arrows), which appears quite thick. This patient also has football sign (straight black arrows) of pneumoperitoneum. Gastrostomy tube (curved arrow) is present in stomach. B, Close-up view of right lower quadrant shows gas outiining both sides of cecal wall (arrows), which is several millimeters thick.
gas outlining
L A
B
.ir’
LEVINE
734
thought to have limited value in diagnosing pneumoperitoneum [10-12]. Our study confirmed that patients with smaller amounts of free air are less likely to have radiologic evidence of pneumoperitoneum on supine films. Nevertheless, one or
Downloaded from www.ajronline.org by 85.202.194.212 on 01/23/19 from IP address 85.202.194.212. Copyright ARRS. For personal use only; all rights reserved
more signs of pneumoperitoneum in 59% of cases. Because life-threatening situation,
these various this condition.
were present on these films
pneumoperitoneum radiologists need
signs and of their relative
may indicate
a
to be aware of value in diagnosing
In our study, the most frequent sign of pneumoperitoneum on supine abdominal radiographs was the right-upper-quadrant gas sign, which was present in 41 % of cases (Fig. 1). Surprisingly, this important sign of pneumoperitoneum has received little attention in the radiologic literature [7-9]. In a retrospective study by Menuck and Siemers [8], localized right-upper-quadrant gas collections were present on supine films in 49% of patients with pneumoperitoneum, whereas the more well-known signs of pneumoperitoneum (i.e., Rigler’s sign and the falciform ligament sign) were present in only
1 7% of patients.
In our study
and that
by Menuck
and
ET AL.
AJR:156,
April 1991
Siemers, these gas collections appeared as obliquely onented, triangular or linear lucencies in the right upper quadrant. It has been postulated that the linear collections represent gas in the right subhepatic space, whereas the triangular collections represent gas in the posterior recess of the right subhepatic space, also known as the hepatorenal fossa or Monison pouch [7-9]. Further analysis of our patients revealed that all of the truepositive right-upper-quadrant gas collections were located in the medial half of the right upper quadrant with an inferolateral to superomedial orientation, and, if triangular, with a concave superolateral border (Fig. 1). In contrast, all of the falsepositive right-upper-quadrant collections had a convex superolateral border or an inferomedial to superolateral orientation or were located in the lateral half of the right upper quadrant (Fig. 2). Thus, if properly interpreted, the right-upper-quadrant
gas sign is probably
the single best sign of pneumopenitoneum
on supine films. The second most frequent sign of pneumopenitoneum on supine abdominal radiographs was Riglen’s sign, which was present in 32% of cases (Fig. 3). However, a false-positive Rigler’s sign was present in five cases (6%) in which there was no evidence of pneumopenitoneum on upright or left lateral decubitus films (Fig. 4). These false-positive findings may have resulted from Mach bands, a phenomenon in which there is the perception of a line at the interface of two regions
of differing densities [1 3]. This problem is more likely to occur when two bowel loops are overlapping, so that the edge of one bowel wall is superimposed on the gas-filled lumen of another loop. However, all of the false-positive cases had an apparent wall thickness of 1 mm or less (Fig. 4), whereas all of the true positives had a wall thickness of 1 mm or greater
(Fig. 3). Thus, evaluation
Fig. 4.-False-positive Rigler’s sign on radiograph in patient without pneumopenltoneum. Note how line (arrows) along margin of bowel has no discernible thickness in this case.
of wall thickness
is a useful criterion
for differentiating Mach bandsfrom true-positive Rigler’s signs in patients with pneumoperitoneum. Furthermore, there were no false-positive cases with gas on both sides of the wall of the stomach, so that the latter finding should be considered a particularly reliable sign of pneumopenitoneum (Fig. 3A). Interestingly, one patient had a variant of Rigler’s sign in which air was only seen outside the wall of several fluid-filled loops of dilated small bowel (Fig. 5). Fig. 5.-Variant pneumoperitoneum.
of Rigler’s sign in patient with Radiograph shows unusually sharp, well-defined outer border (arrow. heads) of several fluid-filled loops of dilated small bowel caused by gas In peritoneal cavity.
Fig.
6.-Falciform
ligament
sign
and
right-
upper-quadrant
gas sign in patient with pneumopenitoneum. Thin, linear, soft-tissue density (black arrow) in right upper quadrant is due to gas outlining falciform ligament. More lateral hiangular
lucency
subhepatic region.
(white
arrow)
is due to gas in
AJR:156,
PNEUMOPERITONEUM
April 1991
Other well-known
signs of pneumoperitoneum
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films, such as the falciform inverted-V sign, were each
ON SUPINE
on supine
ligament sign, football sign, and present in less than 3% of cases
and were always seen in patients who had a positive Rigler’s sign (Fig. 3A) or right-upper-quadrant gas sign (Fig. 6). Thus, for all practical purposes, pneumoperitoneum is primarily diagnosed on supine films by the presence of gas on both sides of the bowel
wall or by triangular
or linear
gas collections
in
the right upper quadrant. Proper interpretation of these signs should lead to more accurate diagnosis of this condition.
REFERENCES 1 . Vaughn RT, Brams WA. Early recognition
of acute perforation of gastric and duodenal ulcer by x-ray examination of spontaneous pneumoperitoneum. Surg Gynecol Obstet 1924;39:610-617 2. Miller RE, Nelson SW. The roentgenologic demonstration of tiny amounts of free intraperitoneal 1971;1 12:574-585
gas:
experimental
and
clinical
studies.
AJR
ABDOMINAL
FILMS
735
3. Rigler LG. Spontaneous pneumoperitoneum: a roentgenologic sign found in the supine position. Radiology 1941;37:604-607 4. Miller RE. Perforated viscus in infants: a new roentgen sign. Radiology 1960;74:65-67 5. Weiner Cl, Diaconis JN, Dennis JM. The Inverted V’: a new sign of pneumoperitoneum.
Radiology
1973;107:47-48
6. Bray JF. The Inverted V sign of pneumoperitoneum. Radiology 1984;151 :45-46 7. Hajdu N, de Lacey G. The Rutherford Monson pouch: a characteristic appearance on abdominal radiographs. Br J Radiol 1970;43:706-709 8. Menuck L, Siemers PT. Pneumoperitoneum: importance of right upper quadrant features. AiR 1976;127:753-756 9. BrilI PW, Olson SR, Winchester P. Neonatal necrotizing enterocolitis: air in Monson pouch. Radiology 1990;174:469-471 10. Berdon WE, Baker DH, Leonidas J. Advantages of prone positioning in gastrointestinal and gastrourological roentgenologic studies in infants and children. AJR 1968;103:444-445. 1 1 . Hamed AK. Diagnosis of pneumoperitoneum in the adult. Nebr Med J 1974;59: 185-191 12. Markowitz 5K, Ziter FM. The lateral chest film and pneumoperitoneum. Mn Emerg Med 1986;15:425-427 13. Edholm P. Boundaries in the radiographic image. I. General principles for perception of boundaries and their application to the image. Acta Radiol 1981;22:457-473
