Large vestibular schwannoma
Large vestibular schwannoma or acoustic neuroma are tumours greater than 3cm in diameter. For this discussion however, every tumour that distorts or displaces the brain is included. Although a schwannoma is considered to be a benign tumour, it occurs in a malignant area (inside the bony internal auditory canal or the skull).
It has the potential to exert pressure and consequently damage nerves, the brainstem and cerebellum. If may lead to increase fluid pressure in the skull (hydrocephalus) and eventually death. Large vestibular schwannoma nearly always grow and therefore have to be managed when diagnosed.
In the 1961 the mortality rate (death rate) in California for surgery for these tumours was 43,5%. Luckily this has improved dramatically over the last decades due to refinement of surgical techniques and better equipment. It is currently less than 1%. Unfortunately, the complications that patients suffer is still fairly high if total removal is attempted. Of these complications, facial nerve injury, hearing loss, cerebrospinal fluid leak, bleeding and other cranial nerve damage are most commonly seen.
Radiation, either using radiosurgery (Gamma Knife) or stereotactic radiotherapy (Linac) is not indicated for treating large vestibular schwannoma. The reason for this is unacceptable high rate of complications of which some may appear years after treatment. Especially temporary swelling of the tumour, cystic changes, chronic imbalance, facial pain and other radiation side effects can occur. Swelling of the tumour may lead to raised intracranial pressure.
The suggested treatment for large vestibular schwannoma therefore is that surgery and radiation is combined. A subtotal removal (STR) of the tumour is much safer and limits the complications. Especially the facial nerve outcomes are much better. After STR the risk of recurrence (re-growth) is low (7% – 32%). Radiation should not be performed routinely in all operated patients but only to those demonstrating recurrence.
All patients should be encouraged to have follow up magnetic resonance imaging (MRI) with contrast after surgery. Volumetric assessments are important to determine recurrence. In those patients displaying recurrence, radiation therapy can be considered.