Temporal Bone Tumors Flashcards
What are the most common skull base neoplasms involving the posterior fossa?
- Common CPA tumors
- Petrous apex lesions
- Uncommon CPA tumors
- Intra-axial tumors
What are examples of common CPA lesions?
- Acoustic neuroma, schwannoma
- Meningioma
- Paraganglioma
- Hemangioma
- Epidermoid tumor
- Nonacoustic neuroma/schwannoma
What is the most common tumor of the temporal bone?
- VS/acoustic neuroma
- Comprise 8-10% of all intra-cranial tumors
- > 90% of all tumors in the CPA
- Benign schwannoma of CN8 (most arrive from vestibular division)
- Site of origin: medial portion of IAC, sometimes CPA
- Diagnosis most often between 30-60 years old
- F>M
- ~95% de novo as unilateral lesion
- Bilateral = NF2
What is the clinical presentation of VSs?
1) Hearing related:
- Unilateral or asymmetric: 95%
- Sudden onset HL: 10-20%
- Tinnitus: HF, constant, unilateral
2) Dysequillibrium: up to 70%
3) Facial hypesthesia: up to 50%
4) Headaches: 40% (brainstem compression)
What are the 3 classifications of VSs?
1) Intracanalicular: <1 cm
2) Intracranial extension without brainstem distortion: 1-2 cm
3) Intracranial extension with brainstem distortion: >2 cm (EX: BS compression, CN 5, hydrocephalus)
How do you diagnose VSs?
- Auditory and vestibular studies
- Imaging studies: definitive diagnosis
- Contrast enhanced MRI = gold standard (isointense on T1-weighted images, some signal increase on T2-weighted images)
- CT w/ contrast (good margins for tumors 1.5 cm+)
What is NF2?
- Multiple neoplasia syndrome
- Mutation of tumor suppressor gene (neurofibromin)
- Inherited as AD trait or de novo
- Nearly 100% penetrance by 60 y/o
- Widely variable phenotype
What are the neurologic manifestations of NF2?
- VS (bilateral: 90-95%; HL and T are presenting sx)
- Meningioma: 45-58%
- Spinal cord ependymomas: 18-53%
- Peripheral neuropathy
What are cutaneous manifestations of NF2?
- Skin tumors: 59-68%
- Skin plaques, subcutaneous tumors, and intradermal tumors
- Cafe au lait maculae
Describe NF2 confirmed/definite diagnosis.
-Bilateral VS
Describe probable diagnosis of NF2.
- First degree relative with NF2 AND EITHER
- Unilateral VS OR
- Two of the following: meningioma, neurofibroma, glioma, schwannoma
Describe the management of VSs.
- Excision to prevent: multiple cranial neuropathies, brainstem compression, hydrocephalus, death
- Stereotactic radiosurgery (gamma knife)
- Radiation treatment
- Pharmacologic treatment
Describe the surgical priorities of for VS management.
- Alleviate risks associated with tumor growth
- Preservation of facial nerve function
- Sparing of hearing
Describe possible surgical outcomes of VS removal.
- Mortality: <2%
- Complications occur in 20% of cases: CSF leak, meningitis, arterial/venous cerebral infarct, postop hemorrhage into CPA, facial nerve damage, HL
Describe hearing outcomes following VS removal.
- Hearing preserved in 25%
- Aidable hearing in ~50%
What surgical approaches for VS are best for complete tumor resection and preservation of FN when serviceable hearing is present?
-No evidence demonstrating superiority of MF vs. RS approaches
What surgical approaches for VS are best for complete tumor resection and preservation of FN when serviceable hearing is not present?
-No evidence demonstrating superiority of TL vs. RS approaches
Does VS size matter for facial and vestibulocochlear nerve preservation with surgical resection?
-Patients with larger tumors should be counseled about the greater than average risk for loss of serviceable hearing
Should small intracanalicular tumors (<1.5 cm) be surgically resected?
-There are insufficient data to support a firm recommendation that surgery be the primary treatment for intracanalicular VSs
Is hearing preservation routinely possible with VS surgical resection when serviceable hearing is present?
-Hearing preservation surgery via MF or RS approach may be attempted in patients with small tumor size (<1.5 cm) and good preop hearing
When should surgical resection be the initial treatment in patients with NF2?
-There is insufficient evidence that surgical resection should be the initial treatment in patients with NF2
Can aspirin halt growth of sporadic VS?
- Possibly
- Aspirin targets the genes/enzymes that mediate inflammation that is up-regulated in sVS
What is a meningioma?
- Lobulated, tough, white-gray mass that is well circumscribed and indents adjacent nervous tissue
- Second most common tumor of the CNS
- Slow growing, benign
- Most commonly diagnosed in middle and late decades
- Often an incidentaloma
What are the signs and sx of meningioma?
- Progressive HL: 60%
- Headaches
- Imbalance
- Tinnitus
- Facial weakness or loss of taste
- Diplopia or visual disturbances
- Dysphagia
Describe the diagnosis of meningioma.
- Audiovestibular testing (can’t differentiate from AN)
- MRI with gadolinium (AN tend to involve entire IAC, dural tail)
- CT
Describe MRI results for meningioma.
- T1: isointense to slightly hypointense in relation to surrounding brain tissue
- T2: less intense than AN
Describe treatment of meningioma.
- Locally destructive and may invade cranial nerves
- Treatment of choice: surgical excision
- Hearing preservation: more likely than AN
- Gamma knife or cyberknife
- Recurrence in up to 30%
What is a facial nerve schwannoma?
- Uncommon temporal bone tumor
- Very slow growing
- Otic capsule erosion: up to 30%
Describe the clinical presentation of FN schwannoma.
- Facial nerve dysfunction (i.e. palsy, twitch)
- Most common pattern: slowly progressive palsy, hyperfunction, recurrent episodes, progressively worse
- Audiovestibular signs and symptoms: CHL with absent AR, SNHL from cochlear invasion, retrocochlear, vertigo from a labyrinthine fistula
What are the clinical findings of FN schwannoma?
- Facial nerve dysfunction: 25-50%
- Mass behind TM: 29%
- MRI: hypointense on T1, hyperintense on T2, enhanced with gadolinium
- CT: osseous erosion
Describe surgical treatment of FN schwannoma.
- Approach varies with location
- Occasionally possible to remove and save nerve
- Nerve can be repaired with an interposition graft
- Longstanding FN palsy (poorer postop FN function)
Describe ABR recording in the OR.
- Stimulus parameters: 20-30/s rate, 95 dB peSPL+
- Earphones: Etymotic ER10A
- Electrodes: EAC linked to Cz or Fpz (tiptrodes)
- Filter settings: 300-1500 Hz
- Acoustic interference during drilling
Describe interpretation of ABRs in surgical context.
- Anesthesia: little effect on ABR
- Brain/brainstem temp: increased absolute, interpeak latencies with decreased temperature
- Craniotomy affects on ABR: removal of CSF, exposure of nerve to air, insertion of retractors (re-establish baseline after opening and placement of retractors)
What are direct 8th nerve action potentials (CNAP)?
- Electrode on cochlear nerve near brainstem root entry
- Stimulus and recording parameters: 64-126 trials at 20/sec, clicks of alternating or fixed polarity, lower amplification gain, same filters as ABR
Describe the detection and interpretation of changes in CNAP.
- Baseline with understanding of inherent variability imperative
- Moving electrode can change response
Describe relationship of FN monitoring to outcomes.
- Small increases in proportion with HB Grades I or II
- Great decrease in incidence of HB Grade V or VI
- Current standard of care in VS surgery
Describe relationship of cochlear nerve monitoring to outcomes.
- ABR sensitive but not specific
- Tumors <2 cm: 30-45% “useful for adequate hearing preservation”
- Success has more to do with surgical approach and identification of small tumors
- CNAP better predictor of outcome than ABR or ECochG
