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Grading of PNI based on extent of invasion as seen on radiographic image
| Grade | Zone involved | Zonal anatomy involved in PNI |
|---|---|---|
| Grade 1 | Zone 1 | Ophthalmic-superior orbital fissure Maxillary-foramen rotundum Mandibular-foramen ovale |
| Grade 2 | Zone 2 | From zone 1 to gasserian ganglion |
| Grade 3 | Zone 3 | Extension into the brain cisterns and brain stem with involvement of zones 1 and 2 |
