(Radiology. 2000;214:157-158.)
© RSNA, 2000
The String of Pearls Sign1
Paul C. Nevitt, MD
1 From the Department of Radiology, Medical College of Virginia of Virginia Commonwealth University, 401 N 12th St, Main Hospital, 3rd Fl, Richmond, VA 23298-0615. Received March 25, 1998; revision requested April 24; revision received July 24; accepted April 24, 1999. Address reprint requests to P.C.N. (e-mail: nevitt@prodigy.net).
Index terms: Intestines, stenosis or obstruction, 74.721, 74.722, 74.723, 74.724 • Signs in Imaging
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APPEARANCE
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The string of pearls sign can be seen on abdominal radiographs obtained with the patient in the upright position or on decubitus abdominal radiographs. Also commonly referred to as the "string of beads sign," the sign consists of a row or line of several small air bubbles obliquely or horizontally oriented in the abdomen (Figure) (1–3).
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Figure 1. String of pearls sign in a patient with small-bowel obstruction (SBO). Left lateral decubitus radiograph of the abdomen demonstrates a row of small air bubbles (arrows), which represents air trapped between the valvulae conniventes.
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EXPLANATION
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The obliquely oriented row of air bubbles represents small amounts of air trapped between the valvulae conniventes along the superior wall of predominantly fluid-filled, dilated small-bowel loops. The meniscal effect of the surrounding fluid gives the trapped air an ovoid or rounded appearance. The appearance of the string of pearls sign depends on the combination of air, fluid-filled bowel loops, and peristaltic hyperactivity.
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DISCUSSION
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Although the string of pearls sign is rarely seen in adynamic ileus, acute gastroenteritis, and saline catharsis, when present in the right clinical setting, it is considered to be virtually diagnostic of SBO (1–4). Mechanical SBO occurs whenever there is an intrinsic or extrinsic blockage of the normal flow of bowel contents. It represents a frequent cause of acute abdomen. The most common cause of SBO in developed countries is adhesions from surgery. Strangulated hernias remain the most common cause of intestinal obstruction in underdeveloped countries (2).
SBO is often difficult to diagnose solely on the basis of conventional radiographic findings. However, sometimes the obstruction may be suggested radiographically before the diagnosis becomes clinically apparent. Horizontal-beam radiographs and radiographs obtained with the patient in the supine position are the initial examinations of choice when SBO is clinically suspected. Maglinte et al (3) found similar accuracies with conventional radiography and computed tomography (CT) in the detection of SBO, but added that CT more frequently enables identification of the cause of obstruction and can provide additional information that is helpful in addressing patient treatment issues. Often, sequential views obtained within a 12–24-hour time frame are helpful in establishing an evolving obstructive gas pattern. Bryk (5) suggested that successive abdominal radiographs obtained in 5-minute intervals are a reliable tool for differentiating mechanical obstruction from adynamic ileus.
SBO typically produces gaseous distention of the bowel loops proximal to the obstructing lesion. Dilated loops of the small intestine usually can be recognized within 3–5 hours after the onset of complete obstruction (2). If the obstructing lesion is somewhat distal, as more loops of bowel become distended with air, they may appear to be stacked on top of each other in a characteristic "stepladder" configuration (6). The dilatation of the small bowel stimulates the mucosa to secrete fluid (2). Thus, the distended bowel contains varying amounts of air and fluid. This accounts for the air-fluid interfaces seen on horizontal-beam radiographs. As the small bowel dilates, the valvulae conniventes widen, and this causes the small bubbles of air to become trapped.
There is much debate regarding the importance of air-fluid levels. More than two air-fluid levels in distended loops of bowel are generally regarded as abnormal. Differential air-fluid levels, that is, two air-fluid levels at different heights within the same loop, were once considered to be indicative of SBO. However, other investigators (4,7) and Gammill and Nice (8) have reported that this finding can be seen frequently in cases of adynamic ileus and is therefore an unreliable indicator of SBO.
In some instances (approximately 6%) of SBO, little or no air is present and the distended bowel loops are predominantly fluid filled (9). These fluid-filled loops may produce soft-tissue opacities, or "pseudotumors," on conventional radiographs (10). Most of the gas proximal to the point of obstruction is from swallowed air. Thus, if patients with SBO swallow little or no air, then supine abdominal radiographs may not demonstrate air distention of bowel. However, upright or decubitus radiographs still may demonstrate air-fluid levels, or, occasionally, the string of pearls sign. Therefore, this sign may indicate the presence of SBO on horizontal-beam radiographs when supine radiographs are indeterminate.
The importance of recognizing the string of pearls sign is often related to the clinical findings of SBO. The classic signs of SBO include abdominal tenderness, distention, and increased high-pitched bowel sounds. However, in cases of complete obstruction with predominantly fluid-filled loops of bowel, there may be much less distention, and the bowel sounds may be normal or diminished because there is little or no air to cause the typical high-pitched gurgling sounds (2,6,9). Knowledge of the radiographic findings of fluid-filled obstructions, including the string of pearls sign, can help to avoid a delay in the diagnosis of SBO when the clinical picture is somewhat confusing.
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Footnotes
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Abbreviation: SBO = small-bowel obstruction
A trainee or resident 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.
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References
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Rennell C, McCort JJ. Bowel gas and fluid. In: McCort JJ, Mindelzun RE, Filpi RG, Rennell C, eds. Abdominal radiology. Baltimore, Md: Williams & Wilkins, 1981; 97-180.
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Herlinger H, Maglinte DDT. Plain film radiography. In: Herlinger H, Maglinte DDT, eds. Clinical radiology of the small intestine. Philadelphia, Pa: Saunders, 1989; 49-53.
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Maglinte DDT, Reyes BL, Harmon BH, et al. Reliability and role of plain film radiography and CT in the diagnosis of small-bowel obstruction. AJR 1996; 167:1451-1455.[Abstract/Free Full Text]
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Levin B. Mechanical small bowel obstruction. Semin Roentgenol 1973; 8:281-297.[Medline]
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Bryk D. Functional evaluation of small bowel obstruction by successive abdominal roentgenograms. AJR 1972; 116:262-275.[Abstract]
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Eisenberg RL. Gastrointestinal radiology: a pattern approach 3rd ed. Philadelphia, Pa: Lippincott-Raven, 1996; 421-431.
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Harlow CL, Stears RLG, Zeligman BE, Archer PG. Diagnosis of bowel obstruction on plain radiographs: significance of air-fluid levels at different heights in the same loop of bowel. AJR 1993; 161:291-295.[Abstract/Free Full Text]
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Gammill SL, Nice CM. Air fluid levels: their occurrence in normal patients and their role in the analysis of ileus. Surgery 1972; 71:771-780.[Medline]
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Williams JL. Fluid-filled loops in intestinal obstruction. AJR 1962; 88:677-686.
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Frimann-Dahl JC. Roentgen examinations in acute abdominal diseases 3rd ed. Springfield, Ill: Thomas CC, 1960.
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