Expansion
Seven and eight ride together through the internal gate
Mnemonic
“7 up, 8 down”, for the arrangement within the meatus:
- Facial nerve (VII) above
- Vestibulocochlear nerve (VIII) below, dividing into cochlear and vestibular parts
- Nervus intermedius, the sensory and parasympathetic root of VII
- Labyrinthine artery
The crowding of VII and VIII explains the cerebellopontine angle syndrome: a vestibular schwannoma (acoustic neuroma) presents with unilateral sensorineural hearing loss and tinnitus first, then an absent corneal reflex as V is involved, then facial weakness, then cerebellar signs.
Bilateral vestibular schwannomas are diagnostic of neurofibromatosis type 2.
Sudden unilateral sensorineural hearing loss requires MRI of the internal acoustic meati, because a schwannoma must be excluded even when the loss recovers.
Expansion
- CN VII - Facial nerve
- CN VIII - Vestibulocochlear nerve