Position and anatomical landmarks
The Gasserion ganglion lies in Meckel's cavity in the cranium close to the petrous bone, part of the temporal bone. The cavernous sinus surrounds the Gasserian ganglion medially, the underside of the temporal lobe superiorly, and the brainstem posteriorly. The ganglion has three branches, from top to bottom: the first branch is the ophthalmic nerve, the second the maxillary nerve, and the third the mandibular nerve. The Gasserian ganglion has a somatotopic arrangement, in that the ophthalmic branch is the most craniomedial and the mandibular branch the most lateral.
The procedure is performed using fluoroscopy, during which the patient lies in a supine position on the table and the C-arm is rotated to obtain a submental view, and is then slowly tilted obliquely towards the affected side until the foramen ovale can be well visualised medially with respect to the mandibular process, and laterally to the maxilla (Figures 1 and 2). The C-arm position is then adjusted such that the foramen is seen as an oval. If the maxillary and mandibular branches are to be treated, the entry point of the needle is 2 cm lateral to the corner of the mouth on the ipsilateral side of the lesion.
Figure 1. Radio-frequency treatment of the Gasserian ganglion: lateral view. The needle is positioned through the base (oval foramen) of the skull. Note the Sella Turcica and Clivus.
The needle is aimed at the middle of the foramen. If only the mandibular branch is to be treated, the entry point of the needle is 1 cm lateral to the corner of the mouth and the needle is aimed at the lateral part of the oval foramen. If only the ophthalmic branch is to be treated, the entry point of the needle lays 3 cm lateral to the corner of the mouth and the needle is aimed at the medial part of the oval foramen. For this treatment, a Sluijter-Mehta-Kanula cannula, 10 cm 22 G with a 2 mm active tip, is used.
Once the anatomical landmarks have been identified, an intravenous sedative dose of propofol or similar agent is given. The Sluijter-Mehta-Kanula needle is then advanced towards the oval foramen (tunnel view; see Figures 1 and 2).
Figure 2. Radio-frequency treatment of the Gasserian ganglion: oblique submental view. The electrode is aimed at the centre of the oval foramen. On the lateral side the mandibula and on the medial side the maxillary sinus.
It is important to place a finger in the mouth in order to ensure that there is no penetration of the oral mucosa. Once the needle has penetrated the foramen ovale into Meckel's cavity, stimulation can take place. The stimulation parameters are as follows: first the motor functions are tested, whereby there should be little or no contraction of the Masseter muscle, preferably above a threshold of 0.6 V. With motor stimulation, the needle should be advanced carefully for approximately 2 mm.
Then, by discontinuing the propofol sedation, the patient is allowed to wake up, and sensory stimulation can be carried out at 50 Hz. Paresthesia should be felt between
0.05 and 0.2 V in the area corresponding to the patient's pain. After appropriate paresthesia, 60°C RF treatment can be carried out for 60 seconds. Thereafter, corneal reflex is tested and the patient is evaluated for hypoesthesia in the treated dermatome. If there is no hypoesthesia, a second treatment is performed at 65°C for 60 seconds, and if there is still no hypoesthesia,a third RF treatment can be carried out at 70°C for a further 60 seconds.
The percutaneous RF procedure has very low morbidity and virtually no mortality.
- Sensory loss in the treated branch
- Paralysis of the Masseter muscle
- Anesthesia dolorosa
- Corneal hypoesthesia and keratitis
- Temporary paralysis of the third and fourth cranial nerves
- Hematoma of the cheek, which generally disappears after a few days