to reach vestibular schwannomas etc Flashcards
middle fossa approach
- 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.
What is the false edge of the petrosal bone?
The groove occupied by the superior petrosal sinus.
What is “Bill bar”?
(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.
What major nerves will be exposed during middle fossa approach?
- The greater superficial petrosal nerve
- CN VII
- CN VIII - vestibular and cochlear portion
Pros and Cons w Translabyrinthin approach
+
* 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.
How to - translabyrinthin
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.
Risks w translabyrinthic approach
- 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
Pros and cons Retrosigmoid approach
What are the three main surgical approaches to remove an acoustic neuroma?
- Retrosigmoid
- Middle fossa
- Translabyrinthine
Which of the approaches are usually called “the workhorse” in skull base surgery?
The retrosigmoid approach.
Where does acoustic neuromas tend to be situated?
They tend to occupy the cerebellopontine angle and are usually found adjacent to the cochlear or vestibular nerve, either intracranially or extraaxially.
How many % of the CPA tumors are meningiomas?
5-10%
If one individual have bilateral acusticus neurinomas it qualifies for a disease. Which?
Neurofibromatosis type 2. NF2.
Where is the genetic defect situated in NF2?
22q12.2 at the location of neurofibromin 2, encoding the Merlin protein.
How many % of patients with acusticus schwanom has bilateral tumors (NF2)?
5%
Which is the most common genetic defect, NF1 or NF2 ?
NF1
Bilateral acutic neurinoma is a hallmark for NF2. Can acustic neurinoma also be associated to NF1?
Yes, but not bilateral. 24% of NF1 patients have ONE acustic neurinoma.
There is a specific histological site where acustic neuromas tend to arise. Which?
At the transition point between glial and schwann-cells -THE Obsteiner-Redlich zone.
Schwanno
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?
Antoni A and Antoni B
What are the normal clinical findings in acusticus neurinoma?
- Hearing impairment (more than 50% of the pt)
- Tinnitus sometimes intermittent,
- Vestibular -instability while moving head and nystagmus.
Finding of vestibular schwannomas on MRI?
contrast is essential, otherwise small tumors might be missed.
* Hypo-isointense on T1.
* Heterogenouos on T2.
* Usually avid conrast enhancement.
Differential diagnosis to Acusticus neurinoma
- 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.
How often does recurrens occur after removal?
less tha 5%
