A 4 mm intracanalicular schwannoma in a working musician
A 47-year-old high-school music teacher and choral conductor is referred with a 5-month history of progressive right-sided hearing loss and constant high-pitched tinnitus. She reports occasional unsteadiness but no vertigo, no facial weakness and no headache. Pure-tone audiometry shows a right sloping sensorineural loss with a four-frequency average of 38 dB and a word recognition score of 88%; the left ear is normal (average 12 dB, word recognition 100%). Gadolinium-enhanced MRI shows a 4 mm enhancing mass confined to the internal auditory canal, with no brainstem contact and no cystic component. She has no neurofibromatosis features and no family history of vestibular schwannoma. She is otherwise healthy, takes no regular medication and has no contraindication to MRI. She asks whether she should 'have it removed now while it is small' and whether radiosurgery will 'burn the hearing'. She is frightened of ending up completely deaf on the right side.
1. How would you counsel her about observation, stereotactic radiosurgery and microsurgery, including the specific hearing-preservation figures and risks relevant to a 4 mm intracanalicular tumour?
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Framing. She has a small intracanalicular schwannoma (Koos grade I) with serviceable hearing (PTA 38 dB, WRS 88%) and a completely normal contralateral ear. All three options are defensible; the decision hinges on how she weighs uncertainty against the risk of single-sided deafness.
- Observation. Pooled cohorts show roughly one third of small tumours grow within 5 years (conventionally defined as a ≥2 mm increase in maximum dimension); the rest remain stable or even shrink. No upfront treatment preserves hearing better than surveillance in the short term. The downsides are that hearing can deteriorate without tumour growth, and follow-up is long-term.
- Stereotactic radiosurgery (typically 12–13 Gy). Tumour control is 90–98% at 5–10 years. Maintenance of serviceable hearing is about 60–70% at 5 years and declines over the following decade; facial weakness occurs in under 1–2%, trigeminal numbness in 1–3%, and the risk of radiation-induced malignancy is negligible for counselling purposes. It does not remove the lesion, so imaging surveillance continues.
- Microsurgery. For a 4 mm tumour, a middle fossa approach gives hearing preservation of roughly 60–70% in high-volume hands, but carries a 2–5% risk of immediate permanent total deafness and 5–10% risk of transient facial weakness. With a normal opposite ear, this is the least attractive first step for her.
Recommendation. Offer observation with a first MRI at 6 months as the proportionate default, present radiosurgery as a legitimate alternative if she cannot tolerate 'watch and wait', and reserve surgery for growth with hearing decline or her informed insistence. Give her the numbers in writing and offer a second consultation.
2. Define what you would accept as tumour growth, and set out a concrete imaging and audiometric follow-up schedule including the stopping rules you would use.
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Definition of growth. Use a reproducible threshold rather than 'looks bigger': an increase of ≥2 mm in the maximum linear dimension on comparable thin-slice sequences, or any new extension into the cerebellopontine angle with brainstem contact, or new cystic enlargement. Compare the same sequence (heavily T2-weighted CISS/FIESTA or thin post-gadolinium T1) on the same scanner where possible, and measure in the axial plane in two dimensions. Inter-observer measurement error for small tumours is around 1–2 mm, which is why single-millimetre 'growth' should not by itself trigger treatment.
Schedule. Baseline audiogram and MRI now; repeat MRI at 6 months to establish the growth trajectory, then annually for 2 years, then every 2 years if stable. Audiogram at every imaging visit, plus immediately if she notices change. Also record tinnitus burden, facial function (House-Brackmann) and balance symptoms at each visit so that symptom change, not just size, feeds the decision.
Stopping rules / triggers to act. (1) Documented growth on two consecutive scans; (2) loss of serviceable hearing (WRS below 50% or PTA worse than 50 dB) attributable to the tumour; (3) new brainstem contact or fourth-ventricle compression; (4) new trigeminal or facial symptoms. At that point, offer radiosurgery (if the tumour remains under about 2.5–3 cm and hearing is worth preserving) or microsurgery, and re-discuss within a defined interval rather than at the next routine scan.
3. Eight months later she returns urgently with a 3-day history of markedly worse right hearing and new roaring tinnitus. PTA has fallen from 38 to 78 dB with WRS 40%; the repeat MRI shows no change in tumour size. Outline your management and what you tell her about prognosis.
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Recognise the entity. This is tumour-associated sudden sensorineural hearing loss, not progression of the schwannoma, and it should be treated as an otologic emergency rather than accepted as the natural history of the disease. The absence of growth on MRI supports that read.
Immediate management. Start high-dose oral corticosteroid (for example prednisolone 1 mg/kg, up to 60 mg daily, tapered over 10–14 days) without waiting for further imaging, provided there is no contraindication; add or substitute intratympanic dexamethasone if she has diabetes, peptic ulcer disease or another steroid contraindication, or if oral therapy fails. Arrange an urgent audiogram at completion of treatment and again at 4–6 weeks. Check for other causes only if the picture is atypical: syphilis serology, and consider a second MRI if there was any doubt about the earlier films. Do not offer 'reassurance only'.
Prognosis and counselling. Recovery in schwannoma-associated sudden loss is poorer than in idiopathic sudden loss - roughly half recover useful hearing, and the chance falls with severity and with delay beyond 2–3 weeks. Explain that this event is exactly the scenario she feared and that it changes the calculus: with hearing now at 78 dB and WRS 40%, the argument for preserving the remaining hearing by avoiding microsurgery is stronger, and if the tumour later grows, radiosurgery becomes the more attractive active option. Document the discussion and bring her follow-up MRI forward.