| Mayo Clinic, USA [14] | 153 cases/50 yr: 3.06 |
| Hussen W. M., Iraq [7] | 8 cases/12 yr: 0.66 |
| Salehian et al., Iran [8] | 97 cases/16 yr: 6.06 |
| O’Neill et al., Ireland [6] | 29 cases/22 yr: 1.3 |
| Wang et al., USA [5] | 29 cases/25 yr: 1.2 |
| Tayyab et al., Pakistan [14] | 8 cases/11 yr: 0.7 |
| Patetsios et al., USA [15] | 29 cases/30 yr: 0.97 |
| The present study, Iraq | 7 cases/4 yr: 1.75 |