to reach vestibular schwannomas etc

Question 1

middle fossa approach

Answer 1

• lumbar drain
• straight incision. In front of tragus 6cm cephalad.
  *temporalis muscle incised vertically along muscle fibres. reflect anteriorly
• craniotomy 4x3cm
• elevate (middle fossa) dura, section middle meningeal artery,
  IDENTIFY and preserve GREATER SUPERFICIAL PETROSAL NERVE. arcuate eminence, V3 and true edge of petrosal bone.
• drill and expose the IAC (internal auditory canal) all the way to Bills bar.
• LOCALISE the FACIAL NERVE WITH THE NERVE STIMULATOR
• Open the IAC dura while avoiding CN VII.
• IDENTIFY CN VII, VIII - vestibular and cochlear portion AND DISSECT THE TUMOR OFF THE NERVE.

Question 2

What is the false edge of the petrosal bone?

Answer 2

The groove occupied by the superior petrosal sinus.

Question 3

What is “Bill bar”?

Answer 3

(TA: crista verticalis) also known as the vertical crest, is a bony anatomical landmark that divides the superior compartment of the internal acoustic meatus into an anterior and posterior compartment.

Question 4

What major nerves will be exposed during middle fossa approach?

Answer 4

• The greater superficial petrosal nerve
• CN VII
• CN VIII - vestibular and cochlear portion

Question 5

Pros and Cons w Translabyrinthin approach

Answer 5

+
* Early id of CN VII - easier to protect.
* Less risk to cerebellum and lower CN (comp to retrosigm).
* Pt not as ill from blood in cisterna Magna etc.
* less muscle trauma - less H/A (comp retrosigm)

-
* Sacrifice hearing
* May take longer than retrosigm
* Possibly higher risk of CSF leak.

Question 6

How to - translabyrinthin

Answer 6

Supine position w shoulder roll.
Some work w neurootologists for IAC and follow up.
Neuromonitoring w facial EMG, SSEP if tumor involves brainstem.
possible need of lumbar drain.
fat graft - always used.

Question 7

Risks w translabyrinthic approach

Answer 7

• CSF leak
• meningitis
• ipsilateral hearing loss (if not already)
• paralysis of ipsilat face
• facial numbness ipsilat
• post op balance diff/vertigo
• brainstem injury w stroke

Question 8

Pros and cons Retrosigmoid approach

Question 9

What are the three main surgical approaches to remove an acoustic neuroma?

Answer 9

• Retrosigmoid
• Middle fossa
• Translabyrinthine

Question 10

Which of the approaches are usually called “the workhorse” in skull base surgery?

Answer 10

The retrosigmoid approach.

Question 11

Where does acoustic neuromas tend to be situated?

Answer 11

They tend to occupy the cerebellopontine angle and are usually found adjacent to the cochlear or vestibular nerve, either intracranially or extraaxially.

Question 12

How many % of the CPA tumors are meningiomas?

Answer 12

5-10%

Question 13

If one individual have bilateral acusticus neurinomas it qualifies for a disease. Which?

Answer 13

Neurofibromatosis type 2. NF2.

Question 14

Where is the genetic defect situated in NF2?

Answer 14

22q12.2 at the location of neurofibromin 2, encoding the Merlin protein.

Question 15

How many % of patients with acusticus schwanom has bilateral tumors (NF2)?

Answer 15

5%

Question 16

Which is the most common genetic defect, NF1 or NF2 ?

Answer 16

NF1

Question 17

Bilateral acutic neurinoma is a hallmark for NF2. Can acustic neurinoma also be associated to NF1?

Answer 17

Yes, but not bilateral. 24% of NF1 patients have ONE acustic neurinoma.

Question 18

There is a specific histological site where acustic neuromas tend to arise. Which?

Answer 18

At the transition point between glial and schwann-cells -THE Obsteiner-Redlich zone.

Question 19

Schwanno

Question 20

Schwannomas are usually made up of two tissue types where spindle cells w elongated nuclei are arranged in different ways. What are these two tissue types called?

Answer 20

Antoni A and Antoni B

Question 21

What are the normal clinical findings in acusticus neurinoma?

Answer 21

• Hearing impairment (more than 50% of the pt)
• Tinnitus sometimes intermittent,
• Vestibular -instability while moving head and nystagmus.

Question 22

Finding of vestibular schwannomas on MRI?

Answer 22

contrast is essential, otherwise small tumors might be missed.
* Hypo-isointense on T1.
* Heterogenouos on T2.
* Usually avid conrast enhancement.

Question 23

Differential diagnosis to Acusticus neurinoma

Answer 23

• acccount for 80-90% of CPA tumors.
• Meningioma 5-10% of CPA.
• Ectodermal inclusion tumors -Epidermoid 5-7% of CPA tumors. (dermoid)
  *Metastases
  *Neuroma from other CN
  Lots of other possible but rare.

Question 24

How often does recurrens occur after removal?

Answer 24

less tha 5%

Question 25

Postop calculation for the patient?

Answer 25

• possibly worsening tinnitus (tinnitus is postop problem in 10-20%)
• Possibly hearing and facial paralysis improvement with time.