Medium vestibular schwannoma without hearing deficit – upfront radiosurgery

SKULL BASE REGION	Cerebellopontine angle/internal auditory canal
HISTOPATHOLOGY	N/A
PRIOR SURGICAL RESECTION	No
PERTINENT LABORATORY FINDINGS	Pretreatment audiogram: Class A hearing bilaterally with word recognition scores at 100% in both ears

Case description

The patient presented at 40 years of age after sustaining a concussion while playing hockey. He developed persistent headaches and feelings of being “dizzy,” which prompted a magnetic resonance imaging (MRI) scan of the brain without contrast, followed by a postgadolinium MRI after an abnormality was noted on the initial images ( Figure 8.36.1 ). There was a contrast-enhancing lesion in the left internal auditory canal (IAC) extending into the cerebellopontine angle (CPA) consistent with a vestibular schwannoma (VS). He denied unilateral hearing loss or tinnitus, facial numbness, hemifacial spasm, or facial weakness. He had no history of vertigo and only reported a feeling of disequilibrium following his head injury. His neurologic examination was normal. His audiogram showed excellent symmetrical hearing in both ears ( Figure 8.36.2 ). His past medical history was unremarkable. He was counseled regarding the management options—observation, microsurgery, and radiosurgery—and chose to proceed with single-fraction stereotactic radiosurgery (SRS) ( Figure 8.36.3 ).

Radiosurgery Machine	Gamma Knife – Perfexion
Radiosurgery Dose (Gy)	12 at the 50% isodose line, maximum 24 Gy 8 isocenters to cover a volume of 2.3 cm
Number of Fractions	1

Critical Structure	Dose Tolerance
Cochlea	Highly controversial, recommend mean <4 Gy
Facial nerve	Single fraction doses <13 Gy appear to be very safe
Brainstem	Very dependent on volume of brainstem irradiated Most cerebellopontine angle tumors can be safely treated with marginal doses ≤16 Gy

Side Effects/Complications	Frequency
Ipsilateral hearing loss	∼50% at 5 years and up to 75% at 10 years after stereotactic radiosurgery
Facial weakness or hemifacial spasm	1%–3% ^,^,
Trigeminal neuropathy	5%–10%, highest with larger tumors
Hydrocephalus	<3%, age and dose >13 Gy are risk factors
Malignant degeneration	<0.2% ^,

Success Rate/Control Rate	Frequency
Unselected, all cases	>92%
Tumors growing >2.5 mm/year	69%
Larger tumors (>10 cc)	85%

Patient outcome

The patient reported no new symptoms or concerns in the first year following radiosurgery. An early postradiosurgery MRI completed 3 months after treatment showed a volumetric increase in the tumor size with associated loss of central enhancement ( Figure 8.36.4 ). Audiology again demonstrated stable and intact left-sided hearing (see Figure 8.36.4 ). Over the subsequent 8 years, serial MRIs showed a marked reduction in the tumor volume, which had largely receded to the confines of the IAC ( Figure 8.36.5 ). He also noted a slight subjective decline in hearing in the treated ear, but still uses that ear to talk on the telephone (see Figure 8.36.5 ). He has had no facial numbness, weakness, or hemifacial spasm, and no disequilibrium.