DOI: 10.1148/radiol.2231000780
(Radiology 2002;223:239-240.)
© RSNA, 2002
The Pseudocalculus Sign1
Polya Samardar, MD
1 From the Department of Diagnostic Radiology, Medical College of Virginia, Virginia Commonwealth University, PO Box 980615, Richmond, VA 23298-0615. Received April 6, 2000; revision requested May 25; revision received October 12; accepted October 18. Address correspondence to the author (e-mail: psamardar@yahoo.com).
Index terms: Bile duct radiography, 766.122 • Bile ducts, abnormalities, 766.131 • Signs in Imaging
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APPEARANCE
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The pseudocalculus sign is a smooth or irregular convex upward termination of the distal bile duct that mimics a distal bile duct calculus at cholangiography.
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EXPLANATION
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Transient physiologic contractions of the sphincteric segment of the distal common bile duct are responsible for producing the pseudocalculus sign. The sphincteric segment is predominantly composed of prominent circular layers of smooth muscle that is anatomically and functionally distinct from the duodenal wall. The sphincteric segment functions as the primary regulator of bile flow into the duodenum (1,2). Investigators have identified rhythmic cycles of contraction and relaxation of the choledochal sphincter that are independent of duodenal motility (3). Contraction of the circular smooth muscles obliterates the common bile duct lumen, while contraction of the longitudinal smooth muscles shortens the distal duct, retracting the closed lumen into the bile duct in some cases. This results in a convex upward termination of the distal duct that mimics a choledochal calculus (Fig 1). Hence, a pseudocalculus defect is seen.
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Figure 1. Frontal T-tube cholangiogram demonstrates a convex upward termination (arrow) of the distal common bile duct secondary to contraction of the sphincteric segment. This mimicking of a distal bile duct calculus is the pseudocalculus sign.
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In addition to the anatomic and physiologic bases of the pseudocalculus sign, it has also been shown that forceful injection of contrast material into the common bile duct can induce prolonged contractions of the sphincteric segment, which increases the potential for observing the sign (4).
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DISCUSSION
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The pseudocalculus sign has been reported at intraoperative, percutaneous, endoscopic, and T-tube cholangiography, as well as at magnetic resonance cholangiopancreatography. Recognition of this phenomenon can prevent unwarranted surgical exploration or interventional instrumentation of the biliary system and associated morbidity. The pseudocalculus sign should be considered a diagnostic feature when an intraluminal filling defect of the distal common bile duct is observed in the absence of either dilatation of the proximal bile duct or obstruction of biliary flow. Other helpful findings associated with the sign include absence of calcification in the region of the filling defect and absence of abdominal pain on injection of contrast material during T-tube cholangiography. Furthermore, it should be noted that the inferior border of the apparent filling defect secondary to the pseudocalculus sign cannot be seen, since it is not truly an intraluminal filling defect (5). Visualization of all borders eliminates the possibility of observing the pseudocalculus sign. The diagnostic feature of the sign is observation of cyclic contraction and relaxation of the sphincteric segment during fluoroscopy. When the sphincter relaxes, the defect disappears. Moreover, intravenous injection of glucagon can relax the sphincter, further supporting the diagnostic possibility of the pseudocalculus sign (Fig 2) (6). While the pseudocalculus sign has been confused most frequently with choledocholithiasis, it may also be mistaken for a tumor or a stricture.
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Figure 2. Frontal T-tube cholangiogram obtained after intravenous administration of glucagon during the same examination. Image shows relaxation of the sphincteric segment, allowing passage (arrow) of contrast material into the duodenum. The pseudocalculus sign is no longer observed.
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In summary, the pseudocalculus sign mimics a filling defect in the distal common bile duct, giving rise to potential false diagnosis of choledocholithiasis. Awareness of this sign and its unique underlying physiologic and anatomic bases can aid in accurate interpretation of cholangiograms.
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FOOTNOTES
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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.
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REFERENCES
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Boyden EA. The anatomy of the choledochoduodenal junction in man. Surg Gynecol Obstet 1957; 104:641-652.
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Wertheimer M, Brooke WS, Koehler PR, Nelson JA. Pseudocalculus of the common bile duct: a dynamic radiographic differentiation from true retained stone. Am J Surg 1975; 130:742-745.[CrossRef][Medline]
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Caroli JP, Porcher P, Pequignot G, Delattre M. Contribution of cine-radiograph to a study of the function of the human biliary tract. Am J Dig Dis 1960; 5:677-696.[CrossRef]
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Beneventano TC, Schein CJ. The physiologic basis of cholangiographic interpretation: pseudocalculus sign and problem of duct spasm. Surgery 1968; 63:673-677.[Medline]
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Mujahed Z, Evans JA. Pseudocalculus defect in cholangiography. AJR Am J Roentgenol 1972; 116:337-341.[Abstract]
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Ferrucci JT, Jr, Wittenberg J, Stone LB, Dreyfuss JR. Hypotomic cholangiography with glucagon. Radiology 1976; 118:466-467.[Abstract]
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