Grade Zone involved Zonal anatomy PN 1 Clinical PNI imaging zone 1 V1: Up to superior orbital fissure, V2: Up to foramen rotundum, V3: Up to foramen ovale and VII: Up to stylomastoid bell or foramen PN 2 Clinical PNI imaging zone 2 V1, V2 and V3: From zone 1 to Gasserian ganglion. VII: Zone 1 to lateral end of IAC including geniculate ganglion and labyrinthine segment of facial nerve PN 3 Clinical PNI imaging zone 3 All nerves proximal to ganglion into the cisterns or into the brain stem

Table 1: Grading of Perineural Invasion (PNI) based on the zonal anatomy of the cranial nerve. Zone 2 and 3 are classified as T4 disease.