1 Vestibular Schwannoma in Neurofibromatosis Type 2

Case 1 Vestibular Schwannoma in Neurofibromatosis Type 2

Burak Sade and Joung H. Lee

Fig. 1.1 T1-weighted postcontrast axial magnetic resonance image showing bilateral vestibular schwannomas. Note the severe compression of the brainstem.

Fig. 1.2 T1-weighted postcontrast axial magnetic resonance image 2 years after surgery showing complete resection of the tumor on the right. At this point, the left-sided tumor was treated with gamma knife radiosurgery.

Clinical Presentation

An 18-year-old left-handed woman with neurofbromatosis type 2 (NF-2) presents with progression of a known vestibular schwannoma (VS).

Three years ago, she underwent Cyberknife fractionated stereotactic radiosurgery to treat a right-sided VS. Over the last few months, she describes episodes of imbalance and “blackouts” without loss of consciousness.

Her family history is signifcant; both her father and sister have NF-2.

Neurologic evaluation shows bilateral papilledema, decreased hearing on the left side (but still serviceable), and complete loss of hearing on the right side.

Magnetic resonance imaging (MRI) of the brain is shown in Fig. 1.1.

Questions

What are the diagnostic criteria of NF-2?

What additional studies are essential for the decision-making process?

What are the main management goals in NF-2 patients?

What are the management options?

What are the most common surgical approaches?

What would be your plan for the right-sided tumor?
She was operated on via a suboccipital retrosigmoid approach, and complete removal of the tumor was achieved with preservation of the facial nerve. During her follow-up, the tumor on the left side showed growth (Fig. 1.2), with worsening of her hearing.
What would be your plan for the left-sided tumor?
What are the outcomes of radiosurgery for VS?

Answers

What are the diagnostic criteria for NF-2?

Bilateral vestibular schwannoma

Family history of NF-2 (first-degree relative) plus unilateral VS

Family history of NF-2 plus two of the following:

– Meningioma, schwannoma (nonvestibular), glioma, neurofibroma, juvenile posterior subcapsular lenticular cataract, or opacity 1
What additional studies are essential for the decision-making process?^2,3
- Audiometric evaluation including pure tone (PTA), speech reception threshold (SRT), and speech discrimination score (SDS) values
- “50/50” rule can be used a cutoff value for serviceable hearing. With PTA showing values <50 dB and speech discrimination with recognition of >50%.
- Computed tomography (CT) scan of the brain to assess bony landmarks and for surgical planning. Also assess the size of the internal auditory canal (IAC) and whether or not there is any dilatation of the canal.
- Other tests that may be helpful include brainstem auditory-evoked responses (BSAER) as preoperative baselines, electronystagmography (ENG), stapedial reflex to assess retrocochlear lesion, and cold calorictesting.^2,3
What are the main management goals in NF-2 patients?
- To preserve serviceable hearing as long as possible
- To decompress the brainstem from the pressure exerted by the right-sided tumor in this case (Fig. 1.1)
- Early counseling about the genetic implications, as well as the need for training in lip reading, and sign language techniques
What are the management options?
- Conservative approach with observation is not a good option in this case. This approach is used in cases of small tumor with serviceable hearing. It consists of serial observation with MRI or CT every 6 months for 2 years, then annually.
- Radiation therapy: External beam radiation or stereotactic radiosurgery (SRS). Gamma knife radiosurgery (a type of SRS) can be used in the following cases:
  - – Poor operative candidates because of other medical problems, age, etc.
  - – Bilateral VS
  - – Tumor progression or tumor residual after surgical resection
  - – Usually cases of small tumor and/or tumors with serviceable hearing
- Surgery is the mainstay of therapy. It is indicated in large- or medium-size tumors with or without serviceable hearing, in signs of brainstem compression, intractable disequilibrium, severe trigeminal symptoms, and hydrocephalus.
- Note that patients with bilateral VS (as opposed to unilateral) tend to be younger, with larger tumors, worse preoperative hearing, and have greater chances of losing either cranial nerve VII or VIII functions during surgical excision of the tumor.^3,4
What are the most common surgical approaches?
- Suboccipital or retrosigmoid
- Translabyrinthine
- Middle fossa
- Combined approaches⁵
What would be your plan for the right-sided tumor?
- Because of the symptomatic increase in size, failure of previous radiation treatment, and absence of hear ing, surgery is indicated on the right-sided tumor.
What would be your plan for the left-sided tumor?
- Both surgery and radiosurgery are options in this case. Surgery may have the added benefit of removing any mass effect on the brainstem. However, surgery has a significant risk of hearing loss on the only functioning side. Our preferred course of action would be to treat the tumor with SRS. This is to preserve hearing in the only side where it is still present. She was treated with gamma knife radiosurgery.
What are the outcomes of radiosurgery for VS?
- This treatment modality has 81% tumor control rate at 15 years with hearing preservation rates of 73% at 1 year and 48% at 5 years.⁶ Preservation of hearing in tumors of this size would be very difficult to achieve with microsurgery.⁷ Therefore, surgery would not be recommended on this side as the first option, as long as she has serviceable hearing.