FISCH classification is used for glomus tumours based on the extension into surrounding anatomic structures. Type A tumour - Tumour limited to the middle ear cleft (glomus tympanicum) Type B tumour - Tumour limited to the tympanomastoid area with no infralabyrinthine compament involvement Type C tumour - Tumour involving the infralabyrinthine compament of the temporal bone and extending into the petrous apex; Type C1 tumour - Tumor with limited involvement of the veical poion of the carotid canal; Type C2 tumour - Tumour invading the veical poion of the carotid canal; Type C3 tumour - Tumour invasion of the horizontal poion of the carotid canal Type D1 tumour - Tumour with an intracranial extension less than 2 cm in diameter; Type D2 tumour - Tumour with an intracranial extension greater than 2 cm in diameter