Relationship between degree of collateral flow and observable laterality of PCA at MRA
| Degree of Collateral Flow (Ipsilateral-Contralateral) | Score of PCA Laterality | ||||||
|---|---|---|---|---|---|---|---|
| 2 | 1 | 0 | |||||
| P4–P2p | P4–P3 | P3–P2p | P2p–P2a | P4–P4 | P3–P3 | P2a–P2a | |
| Prominent | 1 | 8 | 1 | 0 | 1 | 0 | 0 |
| Mild | 0 | 0 | 1 | 1 | 1 | 7 | 0 |
| Absent | 0 | 0 | 0 | 0 | 0 | 3 | 1 |