Chapter 124 Percutaneous Stereotactic Rhizotomy in the Treatment of Intractable Facial Pain

John M. Tew, Jr. , Chad J. Morgan, Andrew W. Grande

Drawing on our 40-year experience in treating patients with trigeminal neuralgia, we describe our strategies in which patients can select the treatment option best suited to their individual needs. The disease course varies for each patient, expressed in the pathophysiologic nuances of the facial pain, medical history, treatment preferences, and outcomes. Therefore, the treatment paradigm should strive to integrate the full complement of modalities, that is, medical and surgical options, to best target that patient’s goals. Surgical options can be divided into physiologic and ablative procedures. Physiologic procedures include microvascular decompression (MVD) or removal of compressive lesions such as tumors. Ablative procedures, that is, all destructive techniques, include radiofrequency rhizotomy, surgical rhizotomy, peripheral neurectomy, glycerol injection, balloon compression, and radiation. Although medical and physiologic therapies are preferred, ablative procedures are considered when high failure rates occur with medical therapies or pre-existing patient morbidities.

In this chapter, we review the most relevant data and classic papers ¹^–⁸ associated with the various physiologic and ablative procedures. Using the experiences of our patients and evidence in the literature, we conclude that the percutaneous techniques, best represented by radiofrequency rhizotomy, provide the most effective and reproducible results, enduring long-term relief from pain, and the fewest side effects when compared with other ablative procedures. Considering these findings and the ongoing refinements in treatment protocols, we now focus our efforts on training in the art and science of these technical procedures, especially for young neurosurgeons and others who treat facial pain. Dedicated to this training effort, our treatment paradigm, with its full complement of modalities, is carefully highlighted in this chapter, and in courses at annual meetings of the American Association of Neurological Surgeons, other educational efforts, websites of professional organizations, and patient support groups (e.g., Trigeminal Neuralgia Association).

Indications and Patient Selection

The diagnosis of typical trigeminal neuralgia should be established before any treatment paradigm is selected. We define the disorder by five criteria: (1) paroxysmal sharp and shooting pain that is characterized by exacerbations and remissions, (2) pain that follows the distribution of the trigeminal nerve, (3) a normal neurologic examination that includes no significant loss of facial sensation, (4) magnetic resonance imaging (MRI) of the brain that demonstrates neither mass lesions nor demyelinating plaques, and (5) pain that is induced by cutaneous stimulation.

All patients with trigeminal neuralgia preferentially undergo a trial of medical therapy using antiepileptic medication (typically carbamazepine). If failure or intolerance of this first-line treatment results, alternative medications include gabapentin, baclofen, and phenytoin. Among patients treated medically, long-term relief fails in about 75% either because of pain recurrence or the development of toxic adverse effects. These patients are ultimately deemed to be surgical candidates.

When surgery is considered, our patients and their families read and listen to a description of the treatment options (including a web-based module) currently proven to control trigeminal neuralgia; we encourage consultation with other patients who have undergone surgical treatment for trigeminal neuralgia. These tactics help to reinforce the patient’s understanding of the procedures and possible undesirable sensory effects. An important part of our consultation is patient education, leading to a more informed decision regarding treatment.

On the basis of our experience and a review of the literature, we conclude the following. First, percutaneous techniques and posterior fossa exploration offer advantages and disadvantages. Second, radiofrequency rhizotomy is the procedure of choice when medications fail and a first surgical treatment is considered to be unsafe. Age is not a reason in itself for rejecting the idea of a craniotomy as an effective treatment because many patients 75 years and older tolerate this procedure extremely well. Third, microvascular decompression of cranial nerve V is recommended for healthy patients, those with isolated pain in the first ophthalmic trigeminal division or in all three trigeminal divisions, and patients who desire no sensory deficit.⁹

Cannulization, Stimulation, and Lesion Production

Using the senior author’s experience in performing more than 4000 percutaneous stereotactic radiofrequency rhizotomies, we describe the three key steps of the procedure as (1) cannulization of the foramen ovale and the trigeminal cistern, (2) stimulation for pain reproduction and determination of intensity threshold, and (3) generation of an effective partial sensory lesion. To this end, we first review the nuances related to the successful cannulization of the foramen ovale and trigeminal cistern. Secondly, we define the subtleties of stimulation that allow for superior lesion production. Finally, we provide an algorithm that allows for the generation of an effective partial sensory lesion. This three-step approach to percutaneous radiofrequency rhizotomy of the trigeminal nerve has proven safe and effective in more than 95% of patients.

Step 1: Cannulation of the Foramen Ovale

One hour before the procedure, 0.4 mg of atropine is administered intramuscularly to reduce oral secretions and prevent bradycardia. The patient is positioned supine on the fluoroscopic table with the head neutral. Next, Hartel’s three anatomic landmarks are plotted on the face: a point beneath the medial aspect of the pupil, a point 3 cm anterior to the external auditory meatus, and a point 2.5 cm lateral to the oral commissure (Fig. 124-1A and B).¹⁰ The first two points provide the rostral/caudal and medial/lateral trajectories for the penetration of the foramen ovale, and the third point is where the needle penetrates the skin of the jaw. The affected cheek is prepared with Betadine (Purdue-Frederick, Norwalk, CT). A 21-gauge spinal needle placed in the deltoid subcutaneous tissue acts as a reference and grounding electrode, or alternatively, a bovie pad can be used.

FIGURE 124-1 Hartel’s anatomic landmarks for access to the foramen of ovale. A, Surgeon marks three points on the patient’s face: a point 3 cm anterior to the external auditory meatus along a line from the external auditory meatus to the tip of the nose (1), a point beneath the medial aspect of the pupil on the lower eyelid (2), and a point 2.5 cm lateral to the oral commissure (3). B, The target is the foramen ovale, at the intersection of a vertical line (in the sagittal plane) extending through the point beneath the pupil (1) and a horizontal line (in the axial plane) through the point anterior to the external auditory meatus (2).

(Printed with permission from the Mayfield Clinic.)

Before cannulization of the foramen, understanding the skull base anatomy and its anatomic variants is essential (Fig. 124-2). Aberrant placement of the cannula can result in unintended neurovascular injuries. Use of lateral fluoroscopic imaging will aid in avoiding the following: cannulization of the inferior orbital fissure (IOF) anterosuperiorly or the jugular foramen posteroinferiorly, or intracranial placement of the cannula through aberrant foramina (e.g., foramen of Vesalius, which lies anteromedial to the foramen ovale, or innominate canal of Arnold, which lies posterior to the foramen ovale). Pulsatile blood flow through the cannula indicates penetration of the internal carotid artery (ICA). Puncture of the ICA can occur in three locations: at the proximal C2 segment at the carotid canal, the C3 segment with the electrode passing through the cartilage of the foramen lacerum, and the cavernous (C4) segment (Fig. 124-3). This third type of penetration was described by Rish,¹¹ who noted that an anteromedial electrode passing through the foramen ovale can penetrate the C4 segment of the ICA. If ICA penetration occurs, the cannula is withdrawn promptly, manual pressure is applied over the posterior pharyngeal space, the procedure is discontinued, and the patient is allowed 24 to 48 hours to convalesce. Ischemic complications, such as hemiparesis, and carotid-cavernous fistula have resulted from puncture of the ICA.¹¹ Generally, arterial punctures are minimized by refraining from broad angular readjustments of the electrode and diligent attempts to avoid trajectories that are either posterolateral or posteromedial to the foramen of ovale; such trajectories jeopardize the carotid canal and foramen lacerum, respectively.

FIGURE 124-2 Skull base foraminae can be punctured with a cannula when targeting the foramen ovale. Inferior orbital fissure (IOF) can be hit by a cannula aimed too anterior and superior to the foramen ovale (FO). Jugular foramen (JF) can be hit by a cannula aimed too posterior and inferior. Internal carotid artery can be hit as it enters the carotid canal (CC), or at the foramen lacerum (FL).

(Printed with permission from the Mayfield Clinic.)

FIGURE 124-3 The ICA can be punctured with a cannula at three points when targeting the foramen ovale. A trajectory angle either too posterior (1) can puncture the C2 portion of the carotid as it enters the petrous bone, a trajectory angle too medial and posterior (2) can puncture the C3 portion of the carotid where it lies within the foramen lacerum covered by a thin shell of bone or after penetration of the foramen ovale, a trajectory too medial and anterior (3) can puncture the C4 segment in the cavernous sinus.

(Printed with permission from the Mayfield Clinic.)

The primary goal of the cannulization step is penetration of the medial portion of the foramen ovale and placement of the electrode’s tip in the retrogasserian rootlets (Fig. 124-4). Using Hartel’s landmarks, we advocate either the direct penetration technique or the sequential palpation in which the surgeon sequentially walks the cannula down the smooth surface of the infratemporal fossa toward the superior-medial aspect of the foramen (Fig. 124-5). If the cannula enters the posterolateral aspect of the foramen, it may elude the trigeminal cistern and not contact the trigeminal ganglion within its dural investment. Additionally, as the electrode is advanced, it may not reach the maxillary or ophthalmic divisions of the rootlet.