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Vestibular Schwannoma

last modified on: Tue, 04/09/2024 - 10:20

GENERAL CONSIDERATIONS

  1. Indications
    1. Middle cranial fossa removal
      1. Tumor less than 2 cm, not in contact with brainstem
      2. Usually for hearing preservation, but also for intracanalicular tumors with poor hearing
      3. Age less than 65 years
    2. Translabyrinthine removal
      1. Tumor in contact with brainstem
      2. Enlarging tumor in patient over the age of 65 years
    3. Observation
      1. Age over 65 years, or medically unfit for surgery, with stable tumor on serial MRI scanning (nonenlarging)
  2. Special Considerations
    1. Type 2 neurofibromatosis
      1. Remove smaller tumor and preserve hearing or auditory nerve for cochlear implant
      2. Remove larger tumor and place auditory brainstem implant during removal of second tumor
    2. Acoustic neuroma in only hearing ear
      1. Remove early if small and either preserve hearing or auditory nerve for cochlear implant
      2. Observe for growth and begin teaching lip reading and sign language for eventual hearing loss
    3. Intracochlear/vestibular tumors
      1. Observe for eventual hearing loss
      2. Perform labyrinthectomy for removal after tumor has destroyed hearing

PREOPERATIVE PREPARATION

  1. History and Physical Exam
    1. Auditory symptoms
      1. Hearing loss, tinnitus, fullness, pressure, recruitment
    2. Vestibular symptoms
      1. Vertigo, dysequilibrium, imbalance with quick turns
      2. Ability to walk on dark, rough surfaces
    3. Cranial nerve dysfunction (especially V, IX, X)
      1. Loss of corneal reflex, facial numbness
      2. Mobility of vocal cords
      3. Mobility of soft palate
    4. Otoscopic exam
      1. Usually a normal mobile drum and exam
    5. Weber and Rinne exam to confirm audiogram
    6. Vestibular testing
    7. Cerebellar function testing
    8. Patient right or left handed?
      1. Speech reception and expression areas in nondominant temporal lobe
  2. Ancillary Testing
    1. Audiogram
      1. High frequency loss most common pattern
      2. Reduced speech discrimination score on side of tumor common
    2. ABR (for MCF approach)
    3. Used as baseline to monitor hearing intraoperatively
  3. Radiological Evaluation
    1. MRI (T1 with and without gadolinium, T2) in both the axial and coronal planes; alternatively, T2 fast spin echo sequencing through IACs only
      1. Characterization of the tumor extent and involvement with intracranial structures and vasculature
    2. Stenvers views of middle cranial fossa floor Help identify amount of bone overlying superior semicircular canal
    3. CXR if indicated by concomitant disease processes
  4. Laboratory Evaluation
    1. Hemoglobin level, PT/PTT
    2. EKG in patients over 35 years or if underlying heart disease present
  5. Consultation
    1. Neurosurgery
      1. Tumor compressing fourth ventricle or hydrocephalus present preoperatively
    2. Medicine
      1. If clearance for surgery needed
  6. Consent for Surgery
    1. Risks inherent to any surgical procedure
      1. Bleeding, infection, scar formation, skin anesthesia, or dysesthesia
      2. Subtotal tumor removal with potential for recurrence
    2. Risks of anesthesia
      1. Death, pneumonia, pulmonary embolism, deep vein thrombosis
    3. Risks of middle cranial fossa surgery
      1. Facial nerve injury
        1. Potential nerve grafting using either the greater auricular nerve or sural nerve
      2. Hearing loss
        1. Complete sensorineural hearing loss from disruption of labyrinthine vasculature or cochlear injury from drill
        2. Conductive hearing loss from injury to middle ear during tumor exposure
      3. Prolonged vestibular dysfunction
      4. CSF leak with the potential for meningitis
        1. Need for lumbar drain
        2. Need for revision surgery
      5. Stroke
        1. Expressive and/or receptive aphasia if nondominant temporal lobe
      6. Intracranial hemorrhage
      7. Seizure
      8. Death
      9. Need for abdominal fat and fascia to close defect
    4. Risks of translabyrinthine approach
      1. Facial nerve injury
        1. Potential nerve grafting using either the greater auricular nerve or sural nerve
      2. Hearing loss
        1. Patient will have no ipsilateral hearing postoperatively
      3. Prolonged vestibular dysfunction
      4. CSF leak with the potential for meningitis
        1. Need for lumbar drain
        2. Need for revision surgery
      5. Intracranial hemorrhage
      6. Stroke
      7. Seizure
      8. Death
      9. Need for abdominal fat and fascia to close defect

NURSING CONSIDERATIONS

  1. Room Setup
    1. See Basic Soft Tissue Room Setup
      1. Mayfield headrest
      2. CUSA (Cavitron Ultrasonic Aspirator), depending on tumor type and size
      3. Microscope with video unit
      4. NIMS (nerve integrity monitor system)
      5. Hot line unit (for solution irrigation)
      6. Sextet suction caddy
  2. Instrumentation and Equipment
    1. Standard
      1. Acoustic Neuroma Instrument Tray
      2. Bien Otologic Electric Drill Tray
      3. Ear Basic Instrument Tray
      4. Ear Microsurgery Instrument Tray
      5. Fischer Bipolar Instrument Tray
      6. Mastoid Instrument Tray
      7. Midas Rex Drill Tray
      8. NIMS, nerve integrity monitor system and probes (Prass probe)
      9. Nerve stimulator control unit and instrument
    2. Special
      1. Micro Neurotology Instrument Tray
      2. House-Urban Middle Fossa Retractor Tray (MCF approach)
      3. Rongeur Tray, Large (TL approach)
      4. Retractor Tray, Small (for harvesting fat, TL approach)
      5. Jannetta Posterior Fossa Retractor Tray (translab approach)
      6. Gantz Micro Forceps Instrument Tray (for MCF approach)
      7. Adson cerebellum retractor, 8 in long, 4 x 4, sharp prongs x 2
      8. 5940 Beaver blade
      9. Bipolar Bayo irrigation forceps, instruments, 8 in, 1.0 mm tip (MCF)
      10. Bipolar irrigating forceps (TL approach)
      11. Neurosurgical cottonoids in a variety in sizes
  3. Medications (specific to nursing)
    1. Antibiotic ointment
    2. Papaverine, 30mg per ml
    3. 1% lidocaine with 1:100,000 epinephrine
    4. Oxycel cotton
    5. Avitene sheet
    6. Ringer's injection, 1,000 ml bag x 6 for irrigation
    7. Ringer's irrigation solution, 1,000 ml bottles, in warmer x 4
  4. Prep and Drape
    1. Prep, 10% providone iodine
      1. Shave ipsilateral cranium 10 cm circumferentially, and left lower abdomen for fat graft.
      2. 10% providone iodine to ipsilateral hemicranium, face, neck, and left lower quadrant; 10% providone iodine to ipsilateral lower leg if sural nerve graft anticipated preoperatively
    2. Drape
      1. Head drape (leave ipsilateral face free of tape)
      2. Towels around head, and towels to square off graft site of translab
      3. Surgeon places NIMS needle electrodes
      4. Clear plastic drape over ipsilateral face and neck. Split sheet around cranium leaving entire ipsilateral face visible. Drainage bag placed 1 cm behind intended incision.
      5. Split sheet around cranium leaving the entire ipsilateral face visible
      6. Clear plastic drape over left lower quadrant site. Cover with a towel and hemostat for easy identification when needed. Cover with separate full sheet.
  5. Drains and Dressings
    1. Antibiotic ointment to incision, then adaptic, fluffs x 3, and Kerlix 4 in x 2
    2. Antibiotic ointment to abdomen, then fluffs, and Elastoplast (for TL only)
  6. Special Considerations
    1. Prep down to clavicle for possible nerve graft; nerve graft will be done with nylon suture (either 8-0, BV130-4, or 10-0, BV75-4).
    2. When requested to watch face for movement, do not stop observing until told to do so by surgeon.
    3. Ringer's injection should be warm (98 to 102°F).
    4. For translab approach, prep and drape left abdomen for a fat graft (used to obliterate the opening into the dura).
    5. Have papaverine, 30mg/ml, on table for all hearing restoration cases.
    6. Ringer's injection should be used for irrigation during drilling and setup to run through the hot lint unit.
    7. When positioning patient, pad patient with foam and tuck both arms with elbow guards. Strap patient to bed securely and test roll side to side to ensure stability. Then, after ipsilateral cranium is shaven (10 cm circumferentially) surgeons will place NIMS electrodes in the orbicularis oris and orbicularis oculi musculature, as well as 2 grounding electrodes in the forehead to monitor the facial nerve. Place electrodes and earphones for ABR monitoring if hearing preservation is being attempted.

ANESTHESIA CONSIDERATIONS

  1. General anesthetic without muscle relaxant
  2. Table rotated 180° from anesthesia personnel
  3. Central lines and arterial lines per anesthesia
  4. Cephazolin 1 gram preoperatively (repeat every 8 hours)
  5. Decadron 6 mg preoperatively (repeat every 6 hours)
  6. Mannitol (250 cc of 20% solution) given at time of incision on MCF approaches

OPERATIVE PROCEDURE (TL APPROACH)

  1. Incision and Elevation of Skin Flaps
    1. Large postauricular parabolic incision beginning 6 cm superior to pinna, extending 6 to 7 cm behind pinna, and down onto skin crease in neck approximately 6 cm inferior to pinna.
    2. Raise skin and subcutaneous tissue flaps anteriorly to level of ear canal in the plane of the temporalis fascia superiorly, occipitalis fascia posteriorly, and the strernocleidomastoid fascia inferiorly. Preserve greater auricular nerve for grafting if necessary.
    3. Raise large Palva flap (from linea temporalis to mastoid tip) up to level of ear canal.
  2. Mastoidectomy
    1. Complete mastoidectomy with skeletonization of the dura from 2 cm posterior to the sigmoid sinus up to the bony labyrinth and down to the jugular bulb.
      1. The entire sigmoid to the jugular bulb should be completely decompressed.
      2. Must bipolar emissary veins.
    2. Skeletonization of the posterior bony canal and facial nerve at the second genu.
    3. Open epitympanum and remove incus and the head and neck of the malleus
    4. Open the facial recess while identifying the facial nerve along it's second genu.
    5. Drill away the mucosa of the lateral portion of the eustachian tube.
      1. Plug eustachian tube with a combination of fascia, muscle, and bone wax.
      2. Block off middle ear with a large muscle plug.
  3. Labyrinthectomy
    1. Remove entire bony labyrinth except for the superior semicircular canal ampulla, which is the superior landmark of the internal auditory canal (IAC) and the principal landmark for the labyrinthine segment of the facial nerve (anterolateral landmark).
    2. Remove bone medial to labyrinth from the middle fossa dural plate to the jugular bulb. Spinal fluid may be seen to escape from cochlear aqueduct in smaller tumors superior to jugular bulb.
    3. Blueline the IAC and provide 280° of exposure medially.
      1. Drill away bone down to the posterior fossa dura.
      2. Beware of lateral IAC superiorly due to facial nerve location.
  4. Identify Facial Nerve at Vertical Crest (Bill's Bar)
    1. Superior semicircular canal ampulla is a landmark for the facial nerve that passes immediately superior and medial to it.
    2. Remove final pieces of bone off of IAC dura with a blunt elevator.
  5. Tumor Removal
    1. Open IAC inferiorly along the inferior vestibular nerve, with a 59-40 Beaver blade.
    2. Bipolar the dura overlying the cerebellum adjacent to opened IAC dura;open this dura with Beaver blade as well.
    3. Separate the tumor from the cerebellum and place neuropaddy cottonoids between them.
    4. Cauterize the small surface vessels; separate the larger vessels away from the tumor.
    5. Identify the VIIth nerve at the vertical crest and separate it from the tumor to the level of the porous acousticus.
    6. Bipolar the tumor pseudocapsule, away from the facial nerve, and debulk the tumor from within using either cup forceps and suction or the CUSA dissector .
    7. Identify the facial nerve medial to the porous. Usually it is directly anterior, but it may be superiorly or inferiorly displaced.
    8. Identify the VIIth and VIIIth nerves at the brainstem.
    9. Perform further debulking as necessary.
    10. Separate the VIIIth nerve and tumor from the VIIth nerve at the brainstem up to the porous (work from both ends of the facial nerve to connect them).
    11. Separate the tumor and associated VIIIth nerve from the brainstem and cerebellum.
  6. Closure
    1. Place Oxycel or Avitene along the brainstem vasculature
    2. Dural repair
      1. Any large dural defects should be closed using either temporalis fascia, fascia lata, or rectus fascia.
      2. All exposed brain should be covered with fascia, even if suture approximation is not possible.
    3. Mastoid/cranial defect
      1. Use left lower quadrant abdominal fat and fascia to close the defect in the mastoid and cranium.
    4. Skin/subcutaneous tissues
      1. Close the Palva flap over the abdominal fat and fascia with interrupted 3-0 vicryl sutures.
      2. Close the subcutaneous tissues with interrupted 3-0 vicryl sutures .
      3. Close skin with 4-0 nylon .
      4. Close the abdominal wound in 2 layers over a Penrose drain.
    5. Bulky mastoid-type dressing with adequate pressure to prevent spinal fluid subgaleal effusion from developing.

OPERATIVE PROCEDURE (MCF APPROACH)

  1. Incision and Elevation of Skin Flaps
    1. Posteriorly based skin flap, beginning in hairline behind pinna, extending superiorly and anteriorly just above pinna to 0.5 cm posterior to temporal tuft of hair; carry incision superiorly 7 cm, then posteriorly 6 to 7 cm
    2. Anteriorly based muscle flap, which is staggered inferiorly in relation to the skin flap
      1. Harvest a large piece of temporalis fascia prior to elevation of the muscle flap (4 x 4 cm)
      2. Should be able to see zygomatic root easily after elevation
    3. Place 2 Adson cerebellar retractors to separate the skin and muscle flaps, exposing the cranium.
  2. Craniotomy
    1. Based on the zygomatic root, a 4 cm wide by 5 cm high bone flap is drawn on the cranium.
    2. Use a 4 mm cutting burr to remove the majority of the bone.
    3. Use a coarse diamond, 4 mm burr, to remove the final layer of bone over the dura.
    4. Branches of the middle meningeal artery will be encountered, which are controlled with bone wax.
  3. Dural Elevation
    1. Circumferentially elevate the dura from the overlying cranium, using the bipolar cautery liberally to stop bleeding from the dura.
    2. Place Oxycel cigars under the bone flap anteriorly, posteriorly, and superiorly.
    3. Elevate the dura along the floor of the middle cranial fossa from posterior to anterior so as not to disrupt the greater superficial petrosal nerve (GSPN).
    4. Identify the arcuate eminence, GSPN, and petrous ridge.
    5. Use cottonoids anteriorly and posteriorly for dural retraction during elevation.
    6. Brisk bleeding from the middle meningeal artery at the foramen spinosum may be encountered and can be controlled with bone wax and Oxycel packing.
    7. Place the House-Urban retractor under the lip of the petrous ridge at the anticipated location of the IAC (based upon the arcuate eminence).
  4. Identification of the IAC
    1. Begin drilling using a diamond burr over the arcuate eminence to identify the location of the superior semicircular canal. The Stenvers x-ray will demonstrate the amount of bone overlying the semicircular canal (SSCC).
    2. Blueline the superior canal.
    3. The IAC is located 60° anterior to the blue lined SSCC.
    4. Drill deep troughs both anteriorly and posteriorly to the IAC, down to the level of the posterior fossa dura.
      1. Exercise caution when drilling laterally, due to the location of the cochlea and ampulla of the SSCC.
      2. Skeletonize the IAC up the level of the transverse crest.
    5. The cochlea is directly inferior to the facial nerve.
      1. As long as one does not drill deep to the facial nerve anteriorly, the cochlea will not be violated.
      2. Identify the labyrinthine segment of the facial nerve at the transverse crest and decompress the meatal foramen a few millimeters.
    6. Remove the last flecks of bone from the IAC dura with a blunt elevator
  5. Tumor Removal
    1. Open the dura of the IAC over the superior vestibular nerve with a 59-40 Beaver blade or 1 mm hook.
    2. Place a direct auditory nerve electrode between the dura of the IAC and the cochlear nerve for monitoring the cochlear action potentials in real time. Prior to this point, the audiologist has been monitoring the hearing using ABR.
    3. Identify the separation between the facial nerve and superior vestibular nerve at the transverse crest.
      1. Separate the facial nerve from the superior and inferior vestibular nerves at this location.
      2. Cut the lateral ends of the vestibular nerves.
    4. Use a 2.5 mm hook to separate the tumor from the facial and cochlear nerves.
      1. Always work from medial to lateral when possible.
      2. When tumor has been separated, cut the medial ends of the vestibular nerves along with the tumor, thus removing the tumor.
    5. Special considerations
      1. In larger tumors, it is often necessary to debulk the tumor as for TL excision, prior to establishing a plane between the facial nerve and the tumor.
      2. If the auditory response demonstrates prolongation of latency or a decrease in amplitude, stop working and place papaverine on a cottonoid along the cochlear nerve for several minutes.
      3. A cochlear nerve that no longer responds intraoperatively may still have hearing postoperatively; unfortunately, the reverse is also true.
  6. Closure
    1. Apply bone wax to all opened air cells.
    2. Place a large muscle plug in the IAC defect.
    3. Place the previously harvested fascia over the entire temporal bone defect.
    4. Use a corner of the bone flap, over the defect to prevent temporal lobe herniation into the middle ear or IAC.
    5. Release the House-Urban retractor and allow the temporal lobe to re-expand.
    6. Ensure an accurate neuropaddy count.
    7. Place 2-0, 3-0, and 4-0 neurolon sutures between the dura and the temporalis muscle to prevent encephalomalacia.
    8. Replace the bone flap.
    9. Close the temporalis muscle with interrupted 3-0 vicryl sutures.
    10. Close the subcutaneous layer with interrupted 3-0 vicryl sutures.
    11. Close the skin with interrupted 4-0 nylon sutures.
    12. Place a large, tight mastoid dressing.

POSTOPERATIVE CARE (TL AND MCF)

  1. Surgical Intensive Care Unit Overnight
    1. Neurological monitoring for intracranial bleed.
    2. No narcotics used except codeine IM.
    3. Droperidol used for nausea.
    4. Control blood pressure to prevent intracranial bleed.
    5. Carefully assess facial nerve function as soon as patient can give reliable exam.
      1. Facial function may decline postoperatively secondary to swelling.
      2. Good function immediately postoperatively generally implies complete return of function if the nerve does not suffer a delayed paralysis.
  2. Postoperative Day 1
    1. Transfer from surgical intensive care unit to general floor
    2. Change dressing
    3. Remove Foley catheter, arterial lines, supplemental oxygen, EKG leads
    4. Hemoglobin level if extensive blood loss intraoperatively
    5. Up to chair (QD)
    6. Clear liquids when nausea is under adequate control; may then advance diet as tolerated
    7. Ambulate with assistance (QD)
    8. Assess facial function and hearing status if MCF (tuning fork exam)
  3. Postoperative Day 2
    1. Remove abdominal Penrose drain (TL only)
    2. Ambulate with assistance
    3. Patient receives a total of 6 doses of antibiotics and steroids unless a facial paresis develops, in which case the steroids are continued for 7 days
  4. Postoperative Day 3
    1. Reservoir test for CSF rhinorrhea (repeat daily): The patient should be asked daily if he or she has a salty taste in mouth, or has noticed any dripping from nose
    2. Change dressing
  5. Postoperative Day 4
    1. MRI scan of operative field to assess completeness of tumor removal and as a baseline to follow the patient for recurrence
    2. Discharge planning
  6. Postoperative Day 5
    1. Discharge home if tolerating oral feeds and ambulating independently
  7. If patient develops CSF leak
    1. Place lumbar drain for 5 full days
    2. Clamp on the morning of postoperative day 6
    3. Test reservoir
    4. If negative, remove drain and observe for 24 hours until discharge
    5. If positive, revision surgery indicated to close leak
      1. Approach depends on hearing status
      2. If hearing absent, obliterate mastoid and eustachian tube
      3. If hearing present, revise MCF and place more fat, fascia, and muscle into the IAC defect; make sure no air cells are unwaxed
      4. Place lumbar drain for 5 full days postoperatively
  8. Postoperative Day 7 to 10 (Return Visit to Clinic)
    1. Remove stitches in scalp
    2. Repeat reservoir test
  9. Six Weeks Postoperatively
    1. Reevaluate patient
    2. Test hearing if MCF approach

REFERENCES

Chen DA, Arriaga MA, Fukushima T. Technical refinements in retraction for middle fossa surgery. Am J Otol. 1998;19:208-211.

Gantz BJ, Harker LA, Parnes LS, McCabe BF. Middle cranial fossa Acoustic neuroma excision: results and complications. Ann Otol Rhinol Laryngol. 1986;95:454-459.

Nadol JB. Cerebellopontine angle tumors. In: Nadol JB, Schuknecht HF, eds. Surgery of the Ear and Temporal Bone. New York, NY. Raven Press, Ltd. 1993:391-413.

Weber PC, Gantz BJ. Results and complications from acoustic neuroma excision via middle cranial fossa approach. Am J Otol. 1996;17:669-675.