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Facial Nerve Decompression

Anatomy and Physiology

The facial nerve supplies all the muscles of facial expression. It starts at the base of the brain and passes through a tortuous course in the skull base before leaving the skull just below the ear. During its passage through the base of the skull it passes very close to the inner ear and the middle ear. Throughout this passage it is enclosed in the bony canal. The narrowest part of the canal is at the site called the geniculate ganglion. This area lies just above the inner ear. Shortly after this the nerve turns through over to 90° before passing backwards through the middle ear space. Any condition which leads to swelling of the nerve is likely to compress the nerve at this point (geniculate ganglion). When the nerve is compressed the nerve function will cease on either a temporary or permanent basis. The purpose of the operation is to remove the bone surrounding the nerve at its most restricted point. By releasing the pressure on the nerve the nerve is more likely to undergo a spontaneous recovery of function.

Indications

    Mr J Hill FRCS

  1. Facial nerve palsy following temporal bone fracture. Fractures of the base of the skull may pass through the temporal bone. The facial nerve and structures of the ear lie in this bone. The facial nerve may be affected either by a haematoma (bruising) of the nerve, a small sharp piece of bone pressing into the nerve, complete division of the nerve or most likely due to a swelling of the nerve in the narrow canal. If the patient develops a complete facial palsy immediately after a head injury the elecrophysiological tests are often organised to give guide lines as to the likely prognosis of the facial palsy. If the tests indicate that the palsy is severe there is still a chance of spontaneous improvement but surgical decompression may be indicated.
  2. Bell's palsy. The vast majority of Bell's palsies make a spontaneous improvement. There is however a small minority that do not make a satisfactory recovery. Electrophysiological tests in the early stages of Bell's palsy may indicate very reduced function and a possible bad prognosis. In this small group of patients there may be a place for surgical decompression of the facial nerve.

Anaesthetic

This is major surgery that takes place under a general anaesthetic in hospital with neurosurgical facilities.

Surgical Technique

The principle of the surgery is to decompress or repair the facial nerve in the area that is damaged. In cases of Bell's palsy this will be in the region of the geniculate ganglion. In cases of fractured skull, 80% will be in the region of the geniculate ganglion and the other 20% will be further down the course of the nerve in the temporal bone.

Decompressing the geniculate ganglion involves approaching the temporal bone from above. Therefore a window of bone is removed from the skull above the ear. The temporal lobe of the brain is then gently moved aside and the bone over the facial nerve close to the inner ear is drilled away. The bony window is then replaced. This is called the "middle fossa approach".

If the damaged section of nerve is in the middle ear or posteriorly in the mastoid section of the temporal bone then the surgeon can decompress the nerve through an incision that runs behind the ear. A combination of both approaches may be needed.

Length of Operation

3 - 6 hours.

Time in Hospital

2 - 5 days minimum.

Time off Work/Limitations

This depends on the surgical approach used. If the middle fossa approach is used recovery period may be several months. If the approach to the middle ear and the mastoid only is required, recovery will be much quicker.

Risks and Complications<