DOI: 10.1148/radiol.2412040700
(Radiology 2006;241:623-624.)
© RSNA, 2006
The Cupola Sign1
Geoffrey B. Marshall, BSc, MD
1 From the Department of Diagnostic Imaging, Foothills Medical Centre, 1403 29th Ave NW, Calgary, AB, Canada T2N 2T9. Received April 21, 2004; revision requested June 29; revision received July 1; accepted July 28.
Address correspondence to the author (e-mail: geoff.marshall{at}calgaryhealthregion.ca).
 |
APPEARANCE
|
|---|
The cupola sign (1) is seen at supine radiography as an arcuate lucency overlying the lower thoracic spine and projecting caudad to the heart (Fig 1). The superior border is well defined and the inferior margin is poorly delineated. The term cupola is used to indicate the inverted cup-shaped configuration of the lucency.
View larger version (144K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1: Single anteroposterior supine radiograph of the chest depicts an arcuate collection of free intraperitoneal air within the median subphrenic space (cupola sign). The superior border is well defined (arrows) compared with the inferior extent of the collection.
|
|
|
EXPLANATION
|
|---|
When the patient is in the supine position, air within the peritoneal cavity (pneumoperitoneum) will preferentially accumulate in the anterior portion of the cavity, beneath the central tendon of the diaphragm and within the median subphrenic space (2). The central tendon of the diaphragm is composed of three leaves: right, left, and central. The central leaf is located anterior (3) and thus the likely site for the accumulation of gas while the patient is in the supine position. The median subphrenic space is located anterior to the stomach and gastrohepatic ligament. Occasionally, the falciform ligament may appear within the lucency, contiguous with its superior border (1).
|
DISCUSSION
|
|---|
Pneumoperitoneum occurs due to any of a wide variety of causes, which may be benign or life-threatening. The most common cause is recent abdominal surgery, after which air is usually resorbed by the patient over the ensuing 3–7 days (4). The duration of resorbtion is dependent on the initial volume of air introduced and the patient body habitus; asthenic patients tend to experience a prolonged postoperative pneumoperitoneum (5). Other iatrogenic causes include peritoneal dialysis and endoscopic procedures (6). Spontaneous pneumoperitoneum is usually the result of a perforated hollow viscus, especially a perforated duodenal or gastric ulcer. The former cause is seen in the case presented, with confirmation of pneumoperitoneum at computed tomography (CT) (Fig 2) (7). Other causes of spontaneous pneumoperitoneum have been described in the literature (4–7).
Upright chest and lateral decubitus abdominal radiography are still considered to be the standard initial radiologic investigation in the diagnosis of pneumoperitoneum. Miller and Nelson (8) showed that as little as 1–2 mL of free air could be detected if a strict protocol of positioning the patient in the left lateral decubitus position for 10–20 minutes and then in the upright position for an additional 10 minutes was followed. This protocol is of limited use for patients with clinical symptoms that preclude a wait of this duration, and in those patients unable to cooperate by maintaining the optimal position described.
There are many useful signs that may contribute to a diagnosis of free air at supine radiography. In a retrospective study done by Menuck and Siemers (9), a diagnosis of free air was made for 56% of patients known to have pneumoperitoneum who underwent supine radiography. This study emphasized a detailed search for lucencies projecting over the right upper quadrant to identify collections of air within the subhepatic space and anterior to the right lobe of the liver. A blinded, retrospective study by Levine et al (10) showed a 59% sensitivity of supine radiography for displaying free air, with right upper quadrant gas being the most common indicator of pneumoperitoneum (44% of cases). In a review of 100 patients with confirmed pneumoperitoneum, Mindelzun and McCort (1) found six patients with radiographs that displayed the cupola sign. For three of the patients, this was the only indicator of free air. For the remaining three patients, the cupola sign was seen in association with air beneath the right and left diaphragmatic leaves. Potential mimics of the sign include air within the lesser sac, air within a high transverse colon, gas within the pericardium or mediastinum, or air within a horizontally oriented stomach (1). Confusion between signs is obviated by identification of rugae or haustra in cases of intraluminal gastric or transverse colonic air or by identification of the falciform ligament superimposed over the lucency, which confirms the anterior location of the air collection in the peritoneal space rather than in the lesser sac. Pneumomediastinum or pneumopericardium should not demonstrate the well-defined superior margin of the cupola sign.
CT is widely considered to be the reference standard for confirming pneumoperitoneum. Stapakis and Thickman compared the sensitivity of CT with the sensitivity of upright chest radiography for the detection of free air in 13 trauma patients who had undergone diagnostic peritoneal lavage. All 13 (100%) patients demonstrated free air at CT, while only five of 13 (38%) patients showed free air at upright chest radiography (11).
Supine radiography remains an invaluable initial investigation in confirming the presence of pneumoperitoneum as a potential source of the patient's symptoms. The cupola sign denotes free intraperitoneal air within the median subphrenic space which may prompt further investigation, particularly in patients in whom the diagnosis is unsuspected.
|
ACKNOWLEDGMENTS
|
|---|
I thank Colette Marshall, BSc, MD for her assistance.
|
FOOTNOTES
|
|---|
| A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.
|
Author stated no financial relationship to disclose.
|
References
|
|---|
- Mindelzun RE, McCort JJ. The cupola sign of pneumoperitoneum in the supine patient. Gastrointest Radiol 1986;11:283–285.[CrossRef][Medline]
- Cho KC, Baker SR. Supine film manifestations of pneumoperitoneum. In: Myers M, ed. Dynamic radiology of the abdomen. 5th ed. New York, NY: Springer-Verlag, 2000; 319–320.
- Agur AM. Grant's atlas of anatomy, 9th ed. Baltimore, Md: Williams & Wilkins, 1991; 137.
- Cho KC, Baker SR. Extraluminal air: diagnosis and significance. Radiol Clin North Am 1994;32(5):829–844.[Medline]
- Felson B, Wiot JF. Another look at pneumoperitoneum. Semin Roentgenol 1973;8:437–443.[CrossRef][Medline]
- Winek TG, Mosely HS, Grout G, Luallin D. Pneumoperitoneum and its association with ruptured abdominal viscus. Arch Surg 1988;123(6):709–712.[Abstract]
- Rice RP, Thompson WM, Gedgaudas RK. The diagnosis and significance of extraluminal gas in the abdomen. Radiol Clin North Am 1982;20(4):819–837.[Medline]
- Miller RE, Nelson SW. The roentgenological demonstration of tiny amounts of free intraperitoneal gas: experimental and clinical studies. Am J Roentgenol Radium Ther Nucl Med 1971;112:574–585.[Medline]
- Menuck L, Siemers PT. Pneumoperitoneum: importance of right upper quadrant features. AJR Am J Roentgenol 1976;127:753–756.[Abstract]
- Levine MS, Scheiner JD, Rubesin SE, Laufer I, Herlinger H. Diagnosis of pneumoperitoneum on supine abdominal radiographs. AJR Am J Roentgenol 1991;156:731–735.[Abstract/Free Full Text]
- Stapakis JC, Thickman D. Diagnosis of pneumoperitoneum: abdominal CT vs. upright chest film. J Comput Assist Tomogr 1992;16:713–716.
TOP
APPEARANCE
EXPLANATION
