List eight causes of a bladder filling defect.

1. Calculus (think paraplegia or bladder outlet obstruction)
2. Clot
3. Cancer (transitional cell cancer, adjacent spread from tumor of the colon or cervix)
4. Ureterocele (halo sign or cobra head)
5. Prostatic enlargement
6. Foreign body
7. Fungus ball
8. Cystitis