Acoustic schwannoma
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Transcript of Acoustic schwannoma
Acoustic schwannoma
Dr amit mch neurosurgery medical college trivandrum
History
• Sir Charles Balance : 1894 first successful removal of a CP angle lesion ?
meningioma• Eduard Sandidort :1777 the first reported pathologic
autopsy of vestibular schwannoma• Thomas Annadale : first succesful removal of vestibular
schwannoma• Cushing - refined surgical technique to reduce mortality
( from >50% to <11%).• Dandy : gross total resection to limit recurrence
• Panse : translabyrinthine approach• House :1960s reintroduced translaby. app. 1961 proposed Mid. Fossa App.• Olivecrona operated on 415 vestibular
schwannomas between 1931 and 1960• Lars Leksell 1950s focussed proton beam
radiation that paved way for SRS
• 18th century surgery: high morbidity & mortality-technique, postop infn, anesthesia, finger enucleation, AICA injury, infarcts
• Morbidity- pain, VII & other CN palsies • 40% mortality in early 20th century; now < 1%• Cushing refined surgical technique• Olivecrona- mortality 19.7% higher morbidity
& mortality(5 times) for bigger tumors
• Other approaches to ↓ morb & mort• Operating microscope• Facial nerve monitoring, ABER, direct cochlear
monitoring• Improved anaesthetic tech.
Pathology
• Misnomer “acoustic neuroma”• Origin- inferior vest. nerve > sup. Vest nerve• rubbery tissue with a nodular surface.• yellow and gray areas • Interspersed foci of hemorrhage and cyst• Encapsulated tumors • nerve of origin can be splayed thinly tumor
• tumor originates in the region of the internal auditory meatus and grows out into the CPA
• “ice-cream cone” shape• Microscopy: Antoni A and Antoni B • Antoni A area : spindle-shaped cells with rod-
shaped nuclei and dense reticulin• palisading of nuclei- verocay body
• Antoni B areas : stellate or spindled-shaped cells; smaller nuclei, less reticulin, prominent cytoplasmic processes, and a loose myxoid stroma
• Predom. Antoni A areas• higher component of Antoni B -cystic tumors.• Foamy histiocytes- bright yellow color• Psammoma bodies
Immunohistochemistry
• schwannomas express nuclear S-100 and vimentin positivity.
• Loss of heterozygosity on 22q and deficiency of the protein merlin : NF2
Clinical presentation
• Triad of ipsilateral sensorineural hearing loss, tinnitus & balance difficulties
• Most common initial symptom is asymmetric hearing loss (Youman)
• Seen in 85% pts and in 65% it is the initial complaint
• Pressure on cochlear nerve in IAC• Insidious & progressive (cf meniere’s)• High freq loss, word discrimination is affected• Diff in telephonic conversation• 10%- sudden hearing loss (infarct)• Sudden or fluctuating hearing loss• Rx :steroids, salt restn, alc -tobacco restrn
• Rollover phenomenon- SDS decrease as the volume of the speech stimulus increases
• SDS decrease out of prop. to decrease in PTA-feature seen in retrocochlear lesions
• tumor size poorly correlates with hearing status
• Persistent tinnitus- most common accompanying sym (Lee et al)
• High pitched• unilateral tinnitus alone• vestibular sym: uncommon PC• Rotational vertigo < 20%• Dysequilibrium: unsteadiness or imbalance• destruction of vestibular fibers is sufficiently slow as
to permit compensation
• Sym from 5th foll by 7th N comp.• Facial numbness foll by facial weakness, otalgia,
taste change (Tr. Size> 2cm)• resilience of motor nerve relative to sensory n.• Facial numbness occurs in about 25%• subjective reduction in sensation that cannot be
documented • Decrease in the corneal reflex generally occurs
earlier
• Facial weakness is uncommon (< 1%) that facial weakness associated with a small- or medium-size tumor should raise suspicion that it is not an acoustic neuroma.
• Sym due to comp of brainstem & other CNs• Tr. > 4cm :obstr HCP- headche• Headache- due to obst. HCP 40-50%• Ataxia, N/V, diplopia, cerebellar signs, lower
CNs –hoarseness, dysphagia; coma, RD
Signs
• SNHL 65% earliest finding• Weber lat to normal ear• Rinne positive (AC > BC)• CR 33%• Nystagmus 26%• Facial hypoesthesia 26% • Facial palsy 12%• Abnormal eye movt 11%
• Papilloedema 10%, Babinski sign 5%• Positive Romberg sign• DDs• Vest. schwannoma m.c. tumor within the CPA
(70% to 80% ) > meningiomas epidermoid• V nerve schwannoma
Occult acoustic neuromas
• Occult acoustic neuromas (Schuknecht) 570 per 100,000 temporal bones• MRI detect tumors at smaller sizes :dilemma
of what to do with small tumors in asympt. Pts• Prop. of tumors that grow - 30% to 85%• growth rate : 0.4 to 2.4 mm/yr• Tumors that grow do so in the first 5 years
after diagnosis (Stangerup et al 522 pts)
• intrameatal 17% and extrameatal 29% tumors have diff. rate of growth within 4 yrs of dx
• Vest. Schwannomas in NF-2 pts occur at a younger age
• Unpredictable growth rate - more rapid growth the younger the patient
NF-2
• bilateral tumors• NF2 tumors present a more complex
approach because attempts at maintaining serviceable hearing need to take into account future growth
• Cystic acoustic tumors- aggressive course rapid neurological deterioration (size)
• High risk of VII n palsy
Evaluation• MRI : Specific “IAC” protocols to evaluate the CPA and bilateral
IACs : high-resolution, thin-cut sequences in a timely manner. (axial)
• Isointense on T1 and hyperintense on T2 • Avid contrast enhancement.• Tumors can have variable enhancement patterns: • Homogeneous (50% to 60%), heterogeneous (30% to 40%), or
cystic (5% to 15%)• Homogeneous small tumors -Antoni A type• Larger, more heterogeneous tumors - mixed Antoni A & B or
only Antoni B
• MRI - size, intracanalicular and CPA comp.• 3-D, fast spinecho• heavily T2-weighted sequences such as FIESTA
and CISS – Cranial nerves• MRI : 98% sensitivity ; 0% false +ve
Cystic schwannoma
FIESTA
CISS
CPA arachnoid cyst
Epidermoidof CPA
• CT performed with bone algorithms • high-riding jugular bulb and its proximity to
the IAC -retrosigmoid approach because it can limit lateral exposure of the tumor - supine P.
• the extent of mastoid and adjacent bone pneumatization (CSF leaks)
• Anteposed sigmoid sinus in translabyrinthine
Audiometry
• PTA : asses both AC (entire sys) & BC • Functionality of hearing – helps in decision
making & baseline for future references• On hearing screening tests an unexplained diff
in PTA of 10-15 db needs to be investigated• High freq loss, which is asymmetric
• Speech discrimination score (SDS)• Normal in CHL, impaired in cochlear lesions
and worst in retrocochlear lesions• WRS – word recog score• Serviceable hearing: 50/50 rule• Gardner –Robertson class I & II • PTA threshold < 50 db & SDS > 50%• 70/30 rule
• Modified Gardner Robertson hearing classf.• Class I – can use phone on that side• Class II – can localise sounds• Unsalvageable hearing : • Serviceable hearing is unlikely to be preserved
post-op if: pre-op SDS < 75%, PTA >25 db, BAER has abnormal wave morphology, or tumor > 2-2.5 cm
• ENG- electro nystagmography• It tests horizontal (lateral) SCC & the superior
vest nerve that innervates it• >20% diff b/n two ears is abnormal• Test may be normal with a small tumor from
IVN• Also, VN fn till all its fibres are lost
• VEMP- Vest evoked Myogenic Potential• Tests saccule (inf vest nerve IVN)• Independent of hearing
• BAER or ABR• Prolonged I-III & I-V interpeak latency• Prognostication- poor wave morphology – lower
chance of hearing preservation even if hearing is good
Pre-op management
• Discussion of all options with pt• Observation: until growth is observed or new
clinical findings • Pt age, hearing status, and size of the tumor –• Observation an acceptable option- small or
medium-sized tumors, elderly pts• Measurable tumor growth on MRI is a good
predictor of future tumor growth- go for surgery
• Follow-up MRI -1 year.• Annual scans for 3 to 5 yrs foll. By• every 2 years until 10 years • every 5 years thereafter
• Patients with useful hearing at the time of diagnosis are likely to lose hearing with a policy of observation
• Hearing loss correlatd to absolute volumetric tumor growth rate (tumor expand out of IAC)
• Word recog. Score- those with 100% -89% remained in class 1 over 4.6 yrs cf 43% with only small loss of upto 10% t Dx
• Risk of hearing loss not related to- age, size or localisation within IAC(all intracanalicular trs)
• 50% deteriorated to lower class in 4.6 yrs• Tumor >15mm higher chance for hearing loss
& facial n injury foll Sx• Presence of cysts• Serviceable & salvageable hearing & ABR• Hearing in opp ear
Algorithm
• Intracanalicular or CPA tumor ≤ 20mm non cystic non NF2- observation with imaging & annual audiology
• Established tr growth – main determinant for Rx
• Tr > 15-20mm : active management (consider age & hearing also)
Treatment option
• Microsurgery• SRS
Surgical treatment
• Retrosigmoid approach• Translabyrinthine approach• Middle fossa approach• Choice of approach:• Salvageable hearing: • Intracanalicular tumor(only few mm extn into
PF) – middle fossa approach
• Tumor extends > few mm into PF – retrosigmoid approach• Non salvageable hearing small tumors- translabyrinthine app tumor too large to remove via translab. App retrosigmoid approach
• Total excision is the goal of Sx• Subtotal resection- large tumor on the only
hearing side or limited life expectancy
Retrosigmoid approach
• Very flexible- can remove small intracanalicular to large tumors compressing brainstem
• Can preserve hearing as well as facial nerve• Position- semisitting, supine, supine-oblique,
park bench, and lateral oblique positions• facial nerve monitoring• ABR monitoring
• Incision - two fingerbreadths posterior to the mastoid ; just superior to the EAC down to
approx 2 cm below the occiput• Limits of craniotomy/ craniectomy• laterally sigmoid sinus, sup. transverse sinus,
inf. horizontal squama, medially 3 to 5 cm
• entry zone - posterior middle third• facial nerve - usually anterior • facial nerve stimulator -confirm the absence of
the facial nerve• Drill bone to open the posterior wall of the IAC• Injury to SCC – wax immediately• The dura covering the canal is removed to
expose the nerves
• tumor is separated from the cochlear and facial nerves –medial to lateral direction
• air cells & hemostasis• Endoscopy• Bone dust, dural closure, cranioplasty
Middle Cranial Fossa approach
• introduced by House• not ideally suited for pts with sig. extracanalicular
extn. - poor visualization of the CPA and BS• supine position ;head turned to opp. side• Lumbar drainage• Incision -begins at the level of the zygoma just
anterior to the tragus and extends superiorly to superior temporal line.
• A 4- by 5-cm bone flap is planned approx two thirds anterior and one third posterior to the EAC.
• The inferior margin should be placed as close to the middle fossa floor as possible.
• A subtemporal craniectomy is performed
• Dissection of dura - post-to-ant direction• Ant. limit of dis.- for. spinosum (MMA)• Landmarks identified before IAC drilling: • Middle meningeal artery• Arcuate eminence ,the GSPN, facial hiatus• arcuate eminence is drilled until the dense
bone of SSC (bluish hue) is seen
• IAC localized using two key angles. • GSPN-SSC angle(100-120°) & the SSC-IAC
angle (60°)• other methods- line II to EAC Ident. head of malleus- GG &
IAC are collinear• Drill IAC using diamond bur mediolaterally• Porus acousticus drilled first
• fundus of the IAC, the vertical crest exposed- separates the Sup. Vest. N. from VII n.
• dura over the IAC is opened, first posteriorly over the Sup. Vest. N. to avoid VII n. injury.
• tumor -usually posteriorly away from VII n.• higher risk to the facial and cochlear nerves
esp if tumor arises from IVN• Endoscope 0° or 30°
Complications
• retraction of the temporal lobe (aphasia, hemiparesis, seizure).
• CSF leakage through unwaxed air cells or through the middle ear, if the tegmen is opened
• postoperative hematoma (EDH)- hitch dura• high-speed drilling- thermal injury –use
diamond drill/ irrigation
• during drilling of bone over the facial nerve there is a small margin for error.
• The SSC, cochlea, and petrous portion of the carotid artery are at risk with this approach
• technically demanding approach- restricted working zone
• Bleeding into PF- go transtentorial or translab.
Translabyrinthine approach
• pioneered by House, otolaryngologist• early identif. of VII n. at IAC fundus • Good app. for pts with large tumors and no
serviceable hearing.(for tumors reaching & app brainstem retrosigmoid probably better)
• not the approach if hearing preservation is the goal .
• supine position with head turned to opp. side• No requirement for a Mayfield head holder• C-shaped incision - extends from 1 cm above ear
and 2 cm behind the postauricular crease to 1 cm posteroinferior to the mastoid tip
• large sup.temp. fascial graft is harvested.• periosteum is elevated to the EAC• access to posterior digastric – graft for packing
middle ear.
• complete mastoidectomy • Skeletonization of the tegmen & bone
overlying sigmoid sinus• large tumors or ant. placed sigmoid additional
bone post. to sigmoid sinus. cutting bur• Bony labyrinth identified• lateral SCC - landmark for facial nerve• labyrinthectomy
• superior petrosal sinus ,the IAC and jugular bulb identified
• The facial nerve is completely skeletonized from the mastoid segment around the genu to the tympanic segment
• vestibule is opened wide with caution -high-riding jugular bulb- limits exp. of IAC in 24% cases (Saleh et al)
• jugular bulb –skeletonized (potential hemorrhage & air embolism).
• skeletonization of the sigmoid sinus, jugular bulb, inferior IAC, and superior auditory canal.
• laterally - Bill’s bar is identified and therefore the anterior superior facial nerve
• Bone between the middle fossa dura and superior IAC is removed and the facial nerve identified
• the posterior fossa dura is incised• posterior tumor jn with cerebellum identified• arachnoid plane between the tumor and the facial
nerve is dissected• Large tumors -intracapsular debulking• inferior aspect of the surgical field -9th and 10th
nerves & PICA -dissected free of tumor.• Sup. aspect – 5th nerve and petrosal vein-in close
contact with tumor
• facial nerve –ant. margin of the tumor; occasionly -top of the tumor.
• The medial dissection is the most challenging portion of the resection because of the associated risk of damage to both the facial nerve and the pons.
SRS
• Leksell’s initial series -the Karolinska Institute 1969 to 1974- 9 pts
• good short term tumor control in 8• post-treatment hearing loss in most pts• high doses of 25 to 35 Gy.• Kondziolka series- 1987 to 1992- 162 pts, 16
Gy, tumor size 2.2cm
• Tumor control (failure of progression requiring surgery)- 98%.
• Facial function -preserved at 5 years in 79%. • Normal trigeminal nerve- 73%• Hearing ability- 51% • 30% pts experienced at least temporary facial
nerve dysfunction and the morbidity associated with trigeminal neuropathy
• Gamma Knife -deliver doses to the periphery -50% of the peak dose delivered to the center.
• Marginal dose lowered to 13 Gy : lowered the rate of facial neuropathy from 29% to 5%
• lowered trigeminal neuropathy to 2%• Tumor control remained same till dose ≤ 10Gy• MRI-based planning - greater precision
• Fractionated stereotactic radiotherapy (FSRT) • Andrews and coworkers radiosurgery vs FSRT• 125 pts• FSRT - higher rate of hearing preservation if
the patient had serviceable hearing• Disadv of FSRT- freq trips
Facial nerve preservation
• Size of tumor - injury more likely larger tumor• tumors > 4 cm: post op H-B score ≥ 3 (65%)• Tumors < 2.5 cm: post op H-B score ≥ 3 (35%)• Facial n dysfn usu normalise at 6 months• Cystic tumors – more chances of VII dysfn may
be due to their large size• Middle fossa app- more chances of VII dysfn
• Radiosurgery : tumor volume and treatment dose - post-treatment facial neuropathy.
• Friedman and colleagues -each cmᶟ increase in tumor volume, the odds of facial weakness increased by 17%
• each 250-cGy increase in dose – eightfold increase in the odds of facial weakness
Hearing preservation
• Tumor size and extn, & preoperative hearing level, - important predictors of hearing preservation
• Middle fossa approach is best for small laterally placed tumors in the IAC. (52% - 100% hearing preservation)
• Satar and co-workers :tumors withextrameatal extension from 10 to 18 mm into the CPA, hearing preservation - 34%
• Retrosigmoid appr. : fnal hearing in 14% - 83% • best results < 1 cm & without sig. CPA extn.• Staeker et al : middle fossa vs suboccipital• Small intracanalicular tumors in 15 patients
matched for audiologic criteria and tr. size. • Superior results with MFA (Post-op PTA & WRS )• Hearing preservation rates : MFA- 57%
Retrosigmoid approach- 47% .
• Kumon et al -tumors 1 -2 cm, MFA – 0 % and retrosigmoid app.- 47%.
• Facial n function was good only in 50% vs 87% in retrosigmoid group
• Hearing preservation difficult for a latency >2 msec ABER in comparison to normal ear
• MFA - good hearing preservation results with small intracanalicular tumors, but as tumor size increases, the results experience a more significant drop-off than with the retrosigmoid approach.
• Hearing preservation is possible even for larger tumors with the retrosigmoid approach in experienced hands.
ComplicationsFacial Nerve Injury
• Direct trauma, stretching, vascular injury, or thermal effects
• vasospasm : nimodipine and HES• anatomic transection of the nerve - immediate
neurorrhaphy should be attempted (Sampath et al : 5 out of 8 pts with anatomic
transection- improved to a H –B gr 3 or 4)• Anastomosis with 9-0 suture
• Interposed sural n. graft may be used.• Prox. stump not available- 12th-to-7th jump graft
using a sural nerve or great auricular n. -- require prolonged training for facial expression and a gold weight is needed for ocular protection.
• Alt : straight end-to-side hypoglossal-facial anast. - better orbicularis oculi innervation
• more technically challenging
• incomplete eye closure – gold weights• prevent exposure keratitis and corneal ulcer• temporal fascia sling
Cochlear N injury
• Two methods of intraoperative cochlear monitoring
• ABR testing - low amplitude of the signals and the 2- to 3-min. lag time during recording.
• ABR testing does not provide imm. feedback• Direct cochlear n monitoring has the advantage of
higher amplitudes and more rapid feedback
• Direct method - retrosigmoid approach -placement of an electrode directly on the cochlear nerve.
• Danner et al : tumors < 1 cm • hearing preservation rate - ABRs -41% • direct cochlear nerve monitoring - 71% • Vasospasm- nimodipine & HES (Strauss et al)
CSF leaks
• 2% to 30%.• 3rd MC complic. after 7th & 8th N injury• ↑ length of hospital stay, ↑ rates of postop.
meningitis, surgical intervention• Nose > incision > ear• Close scrutiny of any exposed air cells &
sealed with bone wax, muscle etc
• Early leaks & delayed leaks• Early leaks – reinforcement• Delayed leaks – L.D or surgical repair• high-volume LP taps (Youman)• incisional CSF (>3 days)- explore the surgical
site for exposed air cells and place a lumbar drain for 5 days
• Refractory CSF leak in a patient without hearing, a blind sac closure of the EAC and packing of the eustachian tube
• hearing preserved- a MCF approach with segmental division of the ipsi. eustachian tube
Vascular complications
• Cushing referred to the cerebellopontine angle as the “bloody angle”
• ischemic and hemorrhagic types• Ischemic complications : inadvertent coagulation
of brainstem arteries that are adherent tumor• Occlusion of the sigmoid or transverse sinus can
lead to venous infarction• 4.7% - sigmoid sinus infarct
• Approx. half of the venous infarcts will have a hemorrhagic component.
• CPA hemorrhages are most commonly related to venous infarction
• AICA is involved in approximately 37% of tumors ranging from 2.5 to 4 cm and in 92% of tumors greater than 4 cm
• The lab. br. of AICA is involved in 40% of tumors < 2.5 cm, 58% of tumors 2.5 to 4 cm, and 100% of tumors > 4 cm
• PICA, SCA, Vertebro-basilar art.
Hydrocephalus
• Obstructive HCP• Communicating HCP smaller tumors < 2 cm (elevated CSF protein levels)• CSF protein levels > 151 mg/dL were 6 times
more likely to have HCP than pts with CSF protein levels < 80 mg/dL
• Symp comm. HCP develop in 11% of pts after FSRT - necrotic debris secondary to radiation
Post-op headaches
• Retrosigmoid approach - higher incidence of persistent postoperative headaches
• ↑ craniectomy vs craniotomy• ↓ incidence- cranioplasty vs without
cranioplasty• amount of bone dust from drilling
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