Medium vestibular schwannoma with 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 D hearing with word recognition scores at 37% and pure tone average of 45 dB in left ear; normal hearing in right ear

Case description

The patient was a nurse who presented at 59 years of age with left-sided tinnitus and noticeable hearing decline over 2 years. A hearing evaluation demonstrated an asymmetric discrepancy and significant left-sided hearing loss ( Figure 8.37.1 ). A magnetic resonance imaging (MRI) scan with gadolinium revealed a contrast-enhancing mass centered in the left cerebellopontine angle (CPA) with a component in the internal auditory canal (IAC), contacting the pons and cerebellum without associated parenchymal edema. The lesion was 1.8 cm in greatest dimension, and most consistent with vestibular schwannoma (VS) ( Figure 8.37.2 ). Treatment was recommended due to the size of the lesion. The patient was counseled on treatment options, and ultimately underwent single-fraction Gamma Knife radiosurgery (GKRS) ( Figure 8.37.3 ).

Radiosurgery Machine	Gamma Knife – Perfexion
Radiosurgery Dose (Gy)	13 at the 50% isodose line, maximum 26 Gy 11 isocenters to cover a volume of 3.52 cm ³
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 following stereotactic radiosurgery
Facial weakness or hemifacial spasm	1%–3% ^,^,
Trigeminal neuropathy	5%–10%, highest with larger tumors
Hydrocephalus	<2%, age and dose >13 Gy are risk factors
Malignant degeneration	<0.02% ^,