Choledocholithiasis occurs in 3.4% of patients undergoing laparoscopic cholecystectomy but more than one third of these pass the calculi spontaneously within 6 weeks of operation and may be spared endoscopic retrograde cholangiopancreatography. Treatment decisions based on assessment by operative cholangiography alone would result in unnecessary interventions in 50% of patients who had either false positive studies or subsequently passed the calculi. These data support a short-term expectant approach in the management of clinically silent choledocholithiasis in patients selected for LC.

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The aero-optical distortions caused by compressible flows have been used by researchers for flow diagnostics and accepted by designers of airborne optical systems as a performance penalty. In order to estimate these distortions, an understanding of the optical distortion mechanism is required. This article examines the mechanisms which produce a variable-density field (and accompanying index-of-refraction field) in a nearly incompressible shear-layer flow. The two-dimensional-shear-layer velocity field was approximated using a discrete vortex model. From this ‘known’ velocity field, the pressure and density fields were determined by iteratively solving the unsteady Euler equations. The resulting index-of-refraction field produced simulated schlieren images which closely resemble experimental schlierens. Optical wavefronts computed from the simulation reasonably match the behaviour of large-scale aberrations measured in a transonic wind tunnel. Small-scale distortions in the experimental data may have been caused by boundary layers on the splitter plate and tunnel walls or by three-dimensional effects that were not simulated.