Can you tell me what it mean when the gallbladder won't show on pipida scan?

Several reasons: Pipida or hida scan is nuclear medicine test for gall bladder function. Gb does not visualize when gb has acute cholecystitis and patient acutely ill. Also patients with chronic gall bladder duct obstruction will not have gb visualization. Sometimes gb will not be seen well in extreme prolonged fasting, wit certain pain meds and when patient fed by tpn, total intravenous nourishment.

Obstruction...: If tracer is not visualized in the gallbladder during the appropriate scanning period, this means there is cystic duct obstruction which is seen with acute cholecystitis. False positives can occur if you ate within a few hours before scan or if you have fasted for more than 24 hours before scan.