List nine causes of an unseen gallbladder with shadowing in the gallbladder fossa on ultrasound.

1. Chronic cholecystitis (gallbladder contracted around stones): wall/echo/shadow sign
2. Emphysematous cholecystitis
3. Porcelain gallbladder
4. Nonfasting patient (normally contracted gallbladder and air in the bowel)
5. Post cholecystectomy (imaging the duodenum instead)
6. Gallbladder obscured by gas
7. Ectopic gallbladder
8. Carcinoma of the gallbladder
9. Metastases to the gallbladder bed