Trigeminal neuralgia is a form of facial pain caused by irritation of the fifth cranial nerve, the trigeminal (thrice-twinned) nerve.
The trigeminal nerve is responsible for sensation in the face, cheeks, mouth and part of the scalp.
Characteristically, severe pain is experienced in the regions supplied by the second and third branches of the trigeminal nerve – in the cheeks or the jaw. The pain can occur spontaneously or be triggered by factors such as wind on the face, chewing, or temperature changes. The pain characteristically abates between attacks. Rarely, the temples, eyes or forehead can be involved.
The cause of this problem is usually irritation of the trigeminal nerve where it leaves the brainstem or more rarely its origin deeper within the brainstem. Systematic anatomical investigations led by the late Peter Janetta (Pittsburg, USA) confirmed that a frequent cause of trigeminal neuralgia is compression and irritation of the nerve by the pulsations of a small artery in close proximity to the nerve.
Other possible causes are
Making the diagnosis of trigeminal neuralgia depends on the careful consideration of clinical symptoms on one hand and high resolution MRI (magnetic resonance imaging) on the other. Special MRI sequences can be used which show in detail the nerve and its neighboring arteries and veins.
There are a number of treatment options available for trigeminal neuralgia. Medical therapy with painkillers is often the first option, usually carried out in conjunction with a consultant neurologist.
In cases in which medical therapy is insufficient, or when the side effects of pain medications are intolerable, a microsurgical decompression of the trigeminal nerve – freeing the nerve from surrounding blood vessels – can be effective.
In contrast to other methods such as thermocoagulation (destruction by applying heat) of the nerve ganglion or sterotactic radiation, microsurgical decompression has the advantage of leaving the nerve structurally intact and thus the normal function of the nerve can usually be preserved.
In otherwise healthy patients in which the risk of a general anaesthesia is low, microsurgical decompression is preferred to the other, more destructive methods.
Microsurgical decompression is carried out under general anaesthesia via a small skin incision behind the ear. A small hole is made in the back of the skull and the operating microscope and endoscope are used to identify the trigeminal nerve and the blood vessel(s) causing the irritation. The blood vessels are carefully mobilised and moved away from the nerve.
A small piece of Teflon foam – an inert, tissue-friendly material – is placed between the nerve and the blood vessel and glued in position to prevent recurrence.
It is critical in such operations to obtain detailed spatial knowledge of the anatomy of each patient, which can vary considerably from person to person.
To avoid unnecessary dissection and possible damage to neighbouring structures, a 3D computerized simulation based on high resolution MRI data is performed prior to each procedure.