primary advantage of the smaller cordotomy-type electrode is that
the lesion can be made with the patient awake so that constant
monitoring can be employed. This possibility relates to the fact
that thermocoagulation of the gasserian ganglion and the divisions
distal to the ganglion causes intolerable pain. whereas coagulation
of the retrogasserian rootlets causes very little. or at least
tolerable discomfort. Monitoring of the patient during lesioning
ensures that corneal sensation is being maintained. that sensory
deficits are not being created in unwanted areas. and that too much
sensory deficit is not being inflicted. Temperature monitoring is
not available with this electrode, but patient monitoring is far
more effective than temperature monitoring. Furthermore. the
temperature required to make a lesion varies according to the
proximity of the electrode to the retrogasserian rootlets. Lower
temperatures are required if the electrode is within the rootlets.
and higher temperatures if it is merely in their vicinity. In one
series. using the temperature monitoring electrode, the final
temperatures ranged from 47° to 108°. This variability emphasizes
the unreliability of depending on temperature alone.
The electrode has a
bared tip 0.4 mm in diameter and 3 mm long.
Its insulation protrudes 2 mm beyond the tip of a
thin-walled 18-gauge lumbar puncture (LP) needle (3 mm
bare and 2 mm insulated). The exposed tip is bent to
permit lateral deviation of the tip when the electrode
assembly is rotated within the LP needle. The hub of the
LP needle acts as the indifferent or ground electrode.
and the bare electrode tip acts as the active
This smaller electrode
makes it possible to spare the third division in cases
of isolated second-division trigeminal neuralgia, in the
majority of cases. Patients appreciate this, in that
they do not like a numb third division when they have no
pain there. A disadvantage of the cordotomy-type
electrode is that precise localization of the electrode
within the rootlets is not always easy to achieve; skill
in the use of the needle must be developed. Also.
because this electrode is smaller. it has a higher
current density and a greater tendency to cause boiling.
If boiling occurs, a gas bubble forms, the milliamperage
falls off, the voltage rises and current flow ceases. A
larger lesion cannot be made at that location, and the
electrode must be moved to a new location if the
procedure has not been completed.
Nevertheless, Tew, Sweet
and others think that temperature
monitoring is an important adjunct. The
temperature-monitoring electrode they use requires a second
indifferent or ground electrode, which may be a cautery plate or a
needle In the forehead or arm. A burn can occur at the
site of the indifferent electrode. The patient must be
protected against pain during the creation of the RF
lesion with the short-acting anesthetic methohexital.
The curved temperature-monitoring electrode developed by
Tew offers considerable advantage over the straight
7.5-mm temperaturemonitoring electrode that was widely used in the
A temperaturemonitoring electrode with an active surface of 5 mm or
less is recommended. A small cordotomy-type electrode, similar to
the one described above, with temperature monitoring
capabilities is now available.
No premedication is used, but on the
patient's arrival in the treatment room, 2 mg of diazepam or 1 mg
of medazolam is given intravenously along with 0.05 to 0.1 mg of
fentanyl. Additional fentanyl may be required. It must be remembered
that too much of this medication may make it difficult for elderly
patients to fully cooperate when the extent of the sensory deficit
The needle site in the cheek is
infiltrated with 1% lidocaine. This provides local anesthesia and
distends the cheek to help prevent penetration of the oral cavity.
If a long needle is used here, there is some risk of anesthetizing
the third division as it emerges from the foramen ovale, which would
preclude satisfactory treatment of the third division.
The only time we put the patient to
sleep is when the needle is passed through the foramen ovale, which
is often the most painful part of the procedure. The short-acting
agent methohexital is then used. Between 30 and 50 mg is usually
adequate. Patients who underwent the procedure using only diazepam
and fentanyl and then
returned and had a second procedure with methohexital were
universally most grateful for the change.
At the time of penetration of the
foramen ovale, or during the lesioning, there may be a remarkable
hypertensive burst in some patients, and deaths have been reported
from hypertensive intracerebral hematomas. The anesthesiologist
should therefore be warned of this possibility, an arterial line
inserted, and measures to control hypertension made available for
immediate use. Continuous monitoring of the ECG is also advised.
If the larger temperature-monitoring
electrode is used, it is usually necessary to use methohexital each
time a lesion is made, although in some cases it is possible to keep
the patient awake after the initial lesions have been made.
the proper anesthetic technique, which apparently provides some
amnesia for the event, and a lesion made in the retrogasserian
rootlets rather than the ganglion, this should not be a particularly
painful procedure. That this is true is evidenced by the readiness
with which patients return for retreatment when it is necessary.
With some experience, one should be able to perform the treatment in
45 min or less.
Penetration of the Foramen Ovale
It is most important to appreciate
that ordinarily the least difficult aspect of the technique is the
penetration of the foramen ovale. Several techniques have been
Most techniques use the
Härtel landmarks initially. The needle
insertion site is 2.5 to 3.0 cm
lateral to the corner of the mouth more medial for third-division
lesions and more lateral for firstdivision lesions. Often the
needle insertion site is a little inferior to a point directly
lateral to the corner of the mouth. A finger must be placed in the
patient's mouth to avoid penetrating the oral mucosa. Meningitis is
a recognized complication of this procedure. In the
frontal view the needle is directed
toward the pupil, and on the lateral view it is directed toward a
point on the zygoma 2.5 cm anterior to the anterior aspect of the
ear canal. It may be possible to pass the needle through the foramen
ovale using only these landmarks, but that is not recommended,
because without additional radiographic assistance the carotid
artery may be punctured or the needle may enter the superior orbital
fissure. The optic nerve has been penetrated by this technique.
Lateral and Anteroposterior
It is recommended that an image intensifier
be used at this point to visualize the lateral orientation of the
needle, which should be aiming at the vertex of the angle produced
by the shadows of the clivus and the petrous ridge. It
is better to enter on the high side of this point, because a lower
orientation may cause the needle to impinge on the petrous ridge
after penetrating the foramen. The needle is adjusted outside the
foramen ovale until this orientation is obtained. The image
intensifier is then rotated to the anteroposterior (AP) projection
and aligned with the orbitomeatal line. This permits visualization
of the internal auditory meatus through the orbit. The target site
in this projection is a point approximately 9 mm medial to the
lateral border of the internal auditory meatus. This point often
coincides with the medial limit of the inferior dip commonly seen on
the medial petrous ridge. When the needle is oriented
in these two planes, methohexital is given, and the needle usually
passes easily through the foramen ovale. A
wrong skull-base foramen cannot be entered if they are used.
It is at this point in the procedure
that a marked rise in blood pressure may occur. Much more rarely,
there is hypotension and bradycardia instead, which usually respond
nicely to atropine. If the carotid artery is punctured while the
surgeon is attempting to penetrate the foramen ovale, the needle is
almost invariably too medial and too inferior in its location. This
is usually an extracranial puncture, and it is not necessary to
abandon the procedure if it occurs; it is merely necessary to
reorient the needle and proceed. Usually, there are no complications
from penetrating the carotid artery.
surgeons visualize the foramen ovale directly on the submentovertex
projection and guide the needle accordingly. Hyperextension of the
head on the neck to obtain this projection may not be well tolerated
by the cervical spine of some elderly patients, and the radiographic
technique is more cumbersome.
Direct Visualization of the
Others prefer to pass the needle
through the foramen ovale
using direct fluoroscopic
visualization of the foramen. The head is hyperextended and
rotated approximately 20 degrees away from the involved side. The
image intensifier is angled approximately 40 degrees from the
vertical and directed at the needle puncture site. The foramen is
then directly visualized on the AP image intensifier. With flexion
and extension of the head, the petrous ridge can be seen rising and
falling behind the foramen. The needle is then passed through the
foramen under direct vision. Revision to the AP projection would be
recommended at this time. It has been recommended that an attempt be
made to pass the needle through the medial aspect of the foramen.
Localization of the Electrode in
the Retrogasserian Rootlets
When the needle has penetrated the
foramen ovale. it is passed to the region of the clivus. at which
point cerebrospinal fluid (CSF) is
usually obtained. It is most desirable
that there be a free flow of CSF from the needle. and the intent
should be to place the electrode in the retrogasserian rootlets
rather than the ganglion.
If the cordotomy-type electrode is now
inserted. the patient frequently flinches or grimaces as the
electrode passes into the retrogasserian rootlets. This is a good
sign that the electrode is in the proper place.
The impedance is usually between 150
and 350 ohms when the electrode is properly positioned. although
is not a necessary part of the
technique. Impedances of 1000Ω or more indicate that the needle tip
is in tissue.
The most important and valuable
indication that the electrode is in the proper position is a low
voltage threshold to 50- to 60-Hz stimulation localized to the
division to be treated. Electric-like paresthesias may be noted at
0.1 to 0.2 V; the lower the better. If more than 0.4 to 0.5 V is
required, the electrode may have to be repositioned. It must be
remembered that when very low voltage thresholds are obtained, the
lesion may be made rapidly at lower current settings of the RF
generator than would otherwise be required. If previous intracranial
procedures have produced some sensory deficit in the face, somewhat
higher voltages may be required before the patient notices the
Rotation of the angled electrode
within the LP needle may shift the response to the stimulation
within the divisions or from one division to another. Changing the
angle of the electrode may make the difference between no lesion and
a very satisfactory one. This, along with adjustment in the depth of
penetration, will aid in proper placement. It must also
be remembered that at times the response to stimulation may be in
one division although the lesion occurs in another. This is another
reason to have the patient awake during the lesion making.
The gasserian ganglion and
retrogasserian rootlets lie on a plane running from superomedial to
inferolateral, and keeping this in mind aids in electrode
positioning. Sometimes a low-voltage response to stimulation can be
obtained only by deflecting the electrode tip by holding the hub in
a more superomedial or inferolateral position. The assembly can then
be held in this position while the lesion is being made.
Occasionally, the route through the foramen ovale is restricted by
bony obstructions that limit manipulation of the electrode within
the retrogasserian rootlets.
stimulation produces a motor response, the electrode is too medial.
A further aid to electrode placement is the roentgenogram, which
should always be obtained before making a lesion. AP
projection through the orbits is of far more value than the lateral
projection. Also, the AP image intensifier is constantly referred to
during the procedure. AP projection will more
consistently provide accurate localization. The reference point
here is the relation of the electrode to the petrous ridge. If in
the AP projection the electrode tip projects above (superior to)
the petrous ridge, great care must be used lest the corneal reflex
be lost, even if the response to stimulation is in the second
division. Most lesions are made with the electrode at or a few
millimeters below the petrous ridge in the region of the internal
auditory meatus, as visualized through the petrous ridge.
Cordotomy - Type Electrode
The first lesion should be made with
the RF generator at a low setting. Usually 10 to 12 V and 60 to 70
mA are used for the first 15- to 20-s lesion. If there is no
resulting sensory deficit in the face, the lesion is enlarged with a
40-s lesion. If there is still inadequate numbness, the current is
increased by 2 units and the 20- and 40-s lesions repeated until a
vigorous pinprick is barely appreciated as painful. Another
endpoint test that it has been found to be useful is to touch the face lightly
with the twisted corner of a single layer of facial tissue. If the
patient cannot feel the lightest touch of the point of this tissue
but does feel the drag of the tissue across the face, the endpoint
has been reached. Many operators prefer to use complete loss of pain
(analgesia) as their endpoint. but this usually represents too much
The final lesion is often made at
approximately 18 V and 90 mA, though a higher current may be
required. The surgeon should be prepared to make multiple
incremental lesions until the desired sensory deficit is obtained.
Intolerable pain is experienced when
the electrode is in the ganglion or distal to it. and anesthesia is
required to make a lesion there. A headache-type pain may be noted
if the electrode burns the dura surrounding the retrogasserian
A burning type of tolerable discomfort
in the face may be noted with the cordotomy-type electrode,
especially when the final lesion is being made. This burning
sensation is frequently noted lateral to the eye when a
second-division lesion is being made and in or anterior to the ear
with a third-division lesion.
It is important to appreciate that
with the smaller cordotomytype electrode and with the electrode
proximal to the ganglion, the lesion is sometimes made with little
or no pain in the face. This seems to be particularly true with
first-division lesions. Neither the patient nor the surgeon may be
aware that a permanent lesion has been made. If the corneal reflex
is to be maintained, it is imperative, therefore, to insist that
the patient tell the surgeon if discomfort is noted in the eye
during lesioning, and also to constantly monitor the ciliary or
eyelid reflex by repeatedly flicking the upper eyelid with a piece
of twisted facial tissue while the generator is on. Often the first
indication that this reflex is being impaired is a decrease in the
consensual blink reflex and somewhat later there is a decrease in
the direct blink reflex. Attention to this reflex is especially
important when there is deep penetration of the electrode as noted
on the AP projection. The
first-division fibers are more sensitive to heat than those in the
other divisions, and this fact is a warning.
It has been possible to stop
first-division pain and preserve the corneal reflex in almost 90
percent of patients with first-division pain by using these
techniques in the awake patient. Preoperative counseling and
planning are important here.
When the electrode has been
satisfactorily placed by the aid of
stimulation and x-ray imaging, 35 to
45 mg of methohexital is given and, when the patient is asleep, the
temperature is raised to 60°C for 60 to 90 s. The face is checked
when the patient awakens, and if more numbness is required,
additional lesions are made with increases of 5°C in temperature up
to 80°C and sometimes 90°C.
As with the smaller electrode, an
attempt should be made to make multiple small lesions rather than
one large one. This approach should not significantly prolong the
procedure. After the initial lesion, which injures the nerve and
reduces further pain, subsequent lesions should be made with the
patient awake to permit sensory monitoring.
1. This is not a stereotaxic procedure
but a free-hand skill that must be learned. The surgeon should not
be in a hurry, and should schedule enough time to do the procedure
2. The RF lesion is both current- and
time-dependent and gradually increases in size over a period of
about 40 s. After 40 to 60 s the lesion cannot be enlarged without
increasing the current (milliamperage).
3. With either type of electrode, a
flush may be noted in the area where sensory deficit is being
created, but a dense lesion can be made with no flush.
4. Patients with multiple sclerosis
and trigeminal neuralgia have twice the recurrence rate, and a more dense lesion is usually necessary.
5. Pain triggered from the second
division but projecting into the first division requires treatment
of the second division only. The first division need be treated only
when there is a trigger site in the first division, which is usually
from touching the eyebrow or hairline.
6. Before making the first lesion, the
patient's face is checked with a pin, and the patient is told that
the aim of the treatment is for the sharp, pricking quality of the
pin sensation to be lost. The patient is also advised to inform the
operator immediately if any pain or discomfort is felt in the eye
while the generator is
on. It is important to make sure that
the patient is actually reporting loss of pain and not loss of
touch; some patients lose track of what is wanted and lead the
procedure toward loss of touch as an end point. An important
question to ask is, "I know you can feel me touch you with this pin,
but does it hurt?".
7. Each time the electrode is moved
during the lesion making, the current settings on the generator must
be returned to a low setting to avoid creating too dense a sensory
deficit -one of the problems of the procedure.
8. By controlling the extent of
sensory and motor deficits, it is possible to treat patients with
bilateral pain without interfering with eating.
9. If difficulty is encountered in
obtaining a low voltage threshold to stimulation or in making a
lesion, it may be necessary to withdraw the needle to the foramen
ovale and reinsert it in the direction where the lowest threshold to
stimulation was obtained. Alternatively, it may be more expeditious
to withdraw the needle from the skin and start all over again.
A consequence of too much numbness is
a higher incidence of annoying paresthesia and dysesthesia in the
face. Although 6 percent incidence of what the patient
considered "annoying" paresthesia and dysesthesia after treatment.
53% of these patients still rated the overall results of the
treatment as good to excellent. In 0.7% of patients, the
dysesthesia was described as moderate to severe; in 3% it
was considered to be severe, and in 0.4% to be intolerable.
These sensations are often described as a burning, drawing,
scratching, or itching sensation or, if the eye is affected, as
feeling like sand or a hair in the eye. There is great variation in
the individual response to numbness in the face. but most patients
tolerate it well and are grateful provided the pain is relieved. It
would appear that the incidence of annoying paresthesias and dysesthesias and of anesthesia dolorosa is higher in older and more
emotionally unstable patients.
TABLE -1 Results and
Complications in Nugent G.R Series of 1456 Procedures in
Result or Complication
Percent or No. of Patients
Total recurrences-early and late
Annoying dysesthesia (53% of patients still rated the
result as good to excellent)
Loss of corneal reflex-intentional in some
V1 pain satisfactorily treated
with preservation of corneal reflex
Significant impairment of motor root
Slight impairment of
4th cranial nerve
6th cranial nerve palsy-transient
Subjective and objective bruit over eye
Meningitis (presumed, culture negative)
Death (myocardial infarction)
True anesthesia dolorosa occur
in only 0.5 percent of patients. Now it is preferable to accept a higher recurrence rate,
and to make multiple, less-dense lesions to reduce the incidence of
annoying paresthesia and dysesthesia.
Neurolytic keratitis may occur in some
patients with corneal anesthesia, and meticulous eye care is
required in the patient with an anesthetic cornea to prevent
blindness. The corneal ulcers are more apt to occur soon after
treatment than later. keratitis have place in (0.4 percent) and only two
patients have lost vision. Fourth and sixth cranial nerve palsies
have been reported following this treatment; they are usually
transient. One transient fourth and one transient sixth
nerve palsy. These palsies
seem to occur more frequently with
deeper and more medial penetrations, as for first-division
variable degree of trigeminal motor paralysis occur in 25%
of cases. Most patients
are unaware of the motor paralysis, even when it is complete, but
some experience the sensation that the ear is "stopped up." This
probably results from paralysis of the tensor veli palatini muscle.
the function of which is to keep the Eustachian tube closed.
Other patients may complain that
their jaws do not meet properly or that their dentures do not fit.
The patient should be reassured that these problems will pass,
usually within 3 to 6 months. Two transient subjective
and objective bruits on the side of the lesion were noted. These were probably
small carotid-cavernous sinus fistulae. Large carotid-cavernous
sinus fistulae have been reported. Post-treatment
headache accompanied by moderate pleocytosis and negative cultures,
which was presumed to represent a chemical meningitis. Meningitis is
a recognized complication of this procedure and can rarely lead to death. Intracerebral abscess has been reported in 7 cases. Prophylactic antibiotics are recommended by some. The major problem with meningitis
appears to be a failure to be aware of it as a possibility and to
treat it immediately.
Intracranial hemorrhage may occur in
the form of subarachnoid hemorrhage or intracerebral hematoma from the hypertension previously described, or by direct
puncture of intracranial vessels as a result of electrode malalignment.
Herpes simplex eruptions occurred
postoperatively in 31% of the patients, and these lesions
can be severe.
Nugent G.R. had two deaths in his series.
One debilitated 89 year old man died 3 days postoperatively from
pneumonia, and a second patient died of a myocardial infarction as
she was leaving the hospital after an uncomplicated treatment.
Upon discharge, the patient is
counseled regarding tapering down the Tegretol or baclofen and is
warned of the remote possibility of meningitis. If corneal
sensation has been lost the patient and family are instructed to use
artificial tears twice a day in the affected eye, to obtain a
protective plastic shield to be attached to eyeglasses when in dusty
atmospheres and, especially, to examine the eye daily for signs of
inflammation. An ophthalmologist is to be consulted upon any
suspicion of inflammation.