Name six causes of nonshadowing intraluminal gallbladder echoes on ultrasound.

1. Small calculi
2. Tumefactive sludge (i.e., calcium bilirubinate and cholesterol crystals)
3. Post lithotripsy (therapy for gallstones)
4. Blood clots
5. Inflammatory mass of debris (e.g., fungus balls)
6. Cholesterol crystals