Vestibular schwannoma technique

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(NOTE: surgery should be considered in patients with symptoms having 2 cm or less intracranial extension, enlargement of tumor after radiation or after observation)

  1. Suboccipital transmeatal approach
    1. incision is 1 cm medial to the mastoid process
    2. with small tumors, CN 8 is usually on the inferomedial side of the tumor and the facial nerve is on the anterior surface
    3. dissection of the tumor usually goes medial to lateral after identifying CN 7 and 8
    4. Facial nerve function is preserved in 96% with intracanalicular tumor but only 60% in those with >4 cm of intracranial extension using this approach
      1. House Brackmann facial nerve grading
        1. 1 – normal
        2. 2 – mild, slight weakness only on close inspection
        3. 3 – moderate: obvious but not disfiguring
        4. 4 – obvious weakness, incomplete eye closure
        5. 5 – severe: barely perceptible motion
        6. 6 – complete paralysis
      2. hearing preservation depends on the size of the tumor; those with tumors > 2 cm have a low probability of hearing preservation
      3. growth of vestibular schwannomas is thought to be around 2 mm/year
  2. Translabyrinthine approach
    1. advantage: minimum cerebellar retraction
    2. disadvantage: always destroys hearing
    3. approach – through the mastoid with the facial nerve running close to the mastoid wall of the tympanic cavity; the genu of the facial canal is just inferior to the lateral (horizontal) semicircular canal and continues inferiorly to emerge below the skull base at the sylomastoid foramen
      1. mastoidectomy is performed looking for the lateral semicircular canal which is an important landmark; after removing the 3 semicircular canals the vestibule is opened
        1. facial nerve is inferior forming a right angle, superior semicircular canal is superior, posterior semicircular canal is posterior and the transverse semicircular canal is seen straight on
        2. once the semicircular canal are removed the interal auditory canal is opened with tumor lying underneath (NOTE: here the proximal facial nerve and superior and inferior vestibular nerves will be seen just under the dura)
      2. the internal auditory canal contains 4 separate nerves: laterally the superior and inferior vestibular nerves separated by the transverse crest and anterior to the superior vestibular nerve the facial nerve which is separated by Bill’s bar; the cochlear nerve is just inferior to the facial nerve
      3. PICA loops up to CN 9 and 10 and AICA forms a loop that protrudes against or into the internal auditory canal
  3. Middle fossa approach – generally favored for small intracanalicular tumors where hearing is to be preserved
    1. temporal craniotomy anterior to the ear and above the zygoma
    2. dura under the temporal lobe is elevated until the arcuate eminence and greater petrosal nerve are identified
    3. bone is removed over the greater petrosal nerve to expose the geniculate ganglion and genu of the facial nerve and the upper wall of the internal auditory canal
    4. NOTE: nervus intermedius will be stretched around the acoustic neuroma
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