Pain

has long been use of peripheral cryoblockade of trigeminal branches, commonly infra-orbital, supra-orbital and supra-trochlear nerves. These techniques may keep the condition under control where peripheral trigger points for the pain are suitably sited.

Gasserian Ganglion Lesions There are three techniques widely used for trigeminal gangliolysis: gangliolysis with anhydrous glycerol, selective retroGasserian RF lesioning and balloon compression of the ganglion. In recent years, stereotactic radiosurgery to the trigeminal ganglion has been developed. The three percutaneous injection techniques share the same anatomical approach as that described by Sweet. An image intensifier is used to identify the foramen ovale in the supine anesthetized patient. A 20-gauge spinal needle (glycerol gangliolysis), RF cannula (RF lesion) or Fogarty catheter (balloon compression) is inserted approximately 3 cm lateral to the corner of the mouth. The needle is advanced in a cephalad direction towards the base of the skull (taking care not to pierce the buccal mucosa), using the medial border of the pupil as an anterior-posterior guide and a point 2.5 cm anterior to the tragus of the ear as a lateral guide. The needle is then "walked off' into the foramen ovale (the position being confirmed by X-ray).

For glycerol gangliolysis, free-flowing CSF is obtained, indicating that the needle now lies within the trigeminal cistern in Meckel's cave. The patient (still anesthetized) is then moved with due care from the supine to the sitting position. Radio opaque dye is injected to outline the bucket shape of Meckel's cave, confirming correct needle placement and also to ascertain the volume of Meckel's cave. Glycerol is then injected according to the volume of the cave. As the glycerol is hyperbaric, the sitting position ensures that the solution is placed at the bottom of the cave, around the maxillary and mandibular branches. Following injection, the patient needs to remain sitting with the head flexed for 1-2 hours following the procedure, to ensure that the solution remains in the correct place.

RF lesioning requires the patient to be conscious, with the needle in Meckel's cave for sensory and motor testing to take place to establish precise positioning of the probe tip. When this has been achieved, anesthesia is re-instituted and lesioning at 60°C for 1 minute takes place. Frequently, flushing of the skin over the lesioned area will be seen. Waking the patient confirms the adequacy or otherwise of the procedure. Repeat lesions may be required at higher temperatures.

Balloon compression requires the passage through the foramen ovale of a Fogarty catheter, which can be inflated with X-ray contrast medium such that a pear-shaped shadow is seen lying in Meckel's cave; compression is maintained for 1 minute.

There are minimal differences between these techniques in terms of outcome; the choice is made with regard to operator experience and training. Some patients find the sleep/wake/ sleep routine of an RF lesion too distressing and will opt for the greater comfort of full general anesthesia, available with balloon compression or glycerol injection.

Radiosurgery is totally non-invasive and may represent the future as equipment becomes more widely available.

Problems associated with Gasserian gangliol-ysis include reduced sensation in the distribution of the nerve roots (trauma to the lips may occur due to inadvertent biting; corneal ulceration may follow ophthalmic division anesthesia), anesthesia dolorosa (the pain, which may be worse than the original pain), infection, hemorrhage, Horner's syndrome and activation of herpes zoster. Success with neurolysis is good (approximately two-thirds of patients experience permanent or long-lasting relief). However, pain may recur at any time, requiring further interventions or medication.Subsequent procedures may be more difficult, especially in those requiring free flow of CSF.

In patients who are relatively fit, microvascu-lar decompression (Janetta's procedure) is used with good results. The procedure involves using sponge to elevate the vessel causing compression of the nerve at the root entry zone. If no vessel is found, then some surgeons will "traumatize" the nerve as a treatment for the pain. Of all the treatments for TN, surgery is associated with the lowest rate of recurrence; however, the main disadvantage is that it involves all the complications associated with posterior fossa surgery [21-23].

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