cholecystectomy. Occasionally, a clip or suture may serve as a nidus for stone formation (Fig. 4.19). Care must be taken not to mistake a pseudo-calculus for a true calculus. The "pseudocalculus sign" may be observed as a transient phenomenon during cholangiography, caused by contraction of the internal choledochal sphincter. Radiographically, a meniscus-shaped defect is seen at the distal CBD (Fig. 4.20A), but it usually disappears rapidly (Fig. 4.20B). In some cases, the defect may persist, becoming difficult to distinguish from a true calculus. The administration of glucagon may relax the sphincter under this circumstance [37,38].
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