36 Ablative Procedures for Trigeminal Neuralgia
Abstract
Ablative procedures are important tools for the clinician involved in the care of the patient with facial pain to understand. For example, in patients with classical trigeminal neuralgia, ablative procedures should be reserved for those patients unsuited (i.e., without MRI-evidence of vascular compression of the trigeminal nerve), unfit (i.e., with comorbidities which preclude a general anesthetic), unable to realize the expected increased durability of microvascular decompression (i.e., with an expected short life-span typically less than five years), or in those patients who have failed microvascular decompression. With other types of facial pain (e.g., as a result of multiple sclerosis lesion/s), ablative treatments directed at the trigeminal ganglion or cisternal portion of the trigeminal nerve are the treatment of choice. In this chapter, the authors review the technical aspects as well as the intended benefits and expected risks of the various ablative procedures.
36.1 Patient Selection
Facial pain is a common and nonspecific symptom that is associated with known and unknown causes. Clinicians often use the term “trigeminal neuralgia” differently. In its most literal connotation, trigeminal neuralgia denotes pain emanating from within the three dermatomes of the trigeminal nerve. Many clinicians, however, reserve the term, trigeminal neuralgia (TN) to signify a more specific disorder, which primarily manifests as attacks of sudden, unilateral, and lancinating facial pain with characteristic triggers (e.g. light touch, cold air). These attacks often result from vascular compression of the intracisternal portion of the trigeminal nerve near its entry into the brainstem. 1 , 2 , 3 In recent years, vascular compression of the trigeminal nerve has been accepted as the most common cause of classical trigeminal neuralgia by the International Headache Society, the International Association for the Study of Pain, and the European Academy of Neurology. 4 , 5 Despite this long overdue acknowledgement, vascular compression of the trigeminal nerve is not involved in every case of classical TN, and incidental vascular compression of the trigeminal nerve can be found in patients without classical TN. 6 How does the clinician make sense of these seeming contradictions in an effort to properly select patients with classical TN for operative management?
Because patients with classical TN who are responding to carbamazepine or oxcarbazepine at the time of surgery, or responded to them in the past, have better outcomes with microvascular decompression (MVD) or any of the ablative procedures, patients should be asked about their past or current antiseizure responsiveness. 7 If they are responding, or have responded, this suggests that they will respond favorably to any of the available operations for classical TN. It is important to note that data regarding the use of ablation, when the diagnosis is not classical TN, is scarce, and that which does exist reveals poor short and long-term results.
36.1.1 Preoperative Evaluation
A patient who is medically fit to undergo MVD should undergo a gadolinium-enhanced MRI with thin-section multiplanar SSFP sequences that are heavily T2-weighted to determine if there is vascular compression, particularly severe compression or distortion along the centrally-myelinated portion of the trigeminal nerve. 8 , 9 , 10 If vascular compression exists, MVD should be considered for those patients presumed to have more than 5–10 years of life remaining. 8 , 11 An ablative procedure is a better option in patients with classical TN without MRI evidence of vascular compression. The early idea that, “There must be a vessel (intraoperatively), and it is my job to find it,” no longer holds in an era of more detailed imaging. 12 Finally, an ablative procedure is likely a better option for those patients with failed or recurrent classical TN following a well-performed initial MVD when repeat MRI fails to identify missed or recurrent vascular compression
Although consensus guidelines for the surgical management of trigeminal neuralgia do not exist, ablative procedures are well indicated in: (a) patients with classical TN medically unfit for the anesthetic and operative rigors of MVD, (b) patients with classical TN without vascular compression, (c) patients with classical TN who have failed prior MVD, and (d) patients with classical TN who have a short life expectancy.
Percutaneous ablative procedures include glycerol rhizolysis of the trigeminal nerve and Gasserian ganglion (GR), radiofrequency rhizolysis of the trigeminal nerve and/or Gasserian ganglion (RF), balloon compression of the trigeminal nerve (BC), and radiosurgical (i.e., using the Leksell Gamma Knife® or Cyber Knife®) rhizolysis of the intracisternal portion of the trigeminal nerve. Open ablative procedures include partial sensory rhizotomy (PSR) (i.e., Dandy’s procedure) and “internal neurolysis” (IN) of the intracisternal portion of the trigeminal nerve.
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