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  • Pain 2014: Refresher Courses, 15th World Congress on Pain Srinivasa N. Raja and Claudia L. Sommer, editors IASP Press, Washington, D.C. © 2014

    439

    42 Fabián C. Piedimonte, MD

    Fundación CENIT para la Investigación en Neurociencias, Caba, Argentina

    Surgical Treatment for Neuropathic Pain

    Educational Objectives 1. Review the background and rational use of inter-

    ventional pain techniques. 2. Assess adequate patient selection, indications, and

    the evidence to support the use of surgical inter- ventional therapies for neuropathic pain.

    3. Identify pros and cons of diff erent surgical abla- tive and functional neurosurgical interventional therapies to help determine the proper choice of technique for the treatment of chronic neuropathic pain.

    Introduction “Any professional who handles pain patients should be familiar with all therapeutic modalities currently available”

    – John Bonica

    According to the defi nition by the International Asso- ciation for the Study of Pain (IASP), neuropathic pain is caused by a lesion or disease of the somatosensory ner- vous system. Its treatment may be diffi cult. Medications and psychotherapy are often insuffi cient to reduce the pain to a tolerable level. In some well-defi ned circum- stances, functional neurosurgery may provide an alter- native treatment strategy. Before deciding on the most appropriate surgical procedure for a particular patient

    with neuropathic pain, the anatomical and physiologi- cal mechanisms involved in the pain must be analyzed carefully. Analgesic surgery, a branch of functional neu- rosurgery, provides some eff ective strategies for those patients in whom less invasive conservative treatment has failed or in cases in which medication causes signif- icant adverse eff ects. Th e fundamental principle to keep in mind is that any indication for an invasive procedure must arise from an interdisciplinary consensus, taking into account a comprehensive evaluation of pain char- acteristics and the psychological condition of the pa- tient. Neurosurgical procedures available for the treat- ment of chronic neuropathic pain can be divided into three broad groups, as follows:

    • Anatomical procedures treating the pain etiology. • Lesional or ablative procedures making selective

    therapeutic lesions in well-defi ned and identifi ed targets demonstrated to sustain pain.

    • Neuromodulation techniques using electrical stimulation or implanted drug delivery systems.

    We will describe each of these groups below.

    Anatomical Procedures In those cases in which neuropathic pain is due to an identifi able anatomical cause, a treatment option is to perform a procedure to correct the disturbance and thus control the symptoms. Th is procedure should

  • 440 Fabián C. Piedimonte

    achieve its goal (pain relief ) without any impact on other neurological functions. Unfortunately, there are few neuropathic pain conditions secondary to a specifi c anatomical disorder that is easily amenable to surgi- cal intervention. A typical example may be trigeminal neuralgia (TN) caused by nerve compression owing to an expansive lesion or secondary to a neurovascular anomaly in the posterior fossa, a situation that is re- solved by microsurgical resection of the lesion or re- ducing the arterial loop responsible for trigeminal irri- tation, respectively (Fig. 1). Another typical example is compressive radiculopathy secondary to disc herniation that is refractory to conservative treatment. In this case, relief of pain is achieved by radicular decompression by microdiscectomy.

    Ablative or Lesional Procedures “Pain may seem to run in front of the knife”

    – Otfrid Foerster

    Th e mechanism of action of ablative procedures is based on the interruption of a nociceptive pathway at any of its levels, or of those structures related to the ori- gin and/or maintenance of the pain. Th e interruption of nociceptive information is performed via various ablative techniques such as the use of surgical sections, neurolytic agents (phenol, alcohol, etc.), radiofrequen- cy (RF), cryosurgery, and radiosurgery, among oth- ers. Whereas ablative techniques were commonly used during the past century, particularly for cancer pain

    management, their use has been limited today owing to their irreversibility, morbidity, the high incidence of deaff erentation pain, and the emergence of modern, less risky, and more eff ective options.

    From a topographic point of view, ablative pro- cedures can be grouped into peripheral procedures (neurectomy, gangliectomy, rhizotomy, and sympa- thectomy), spinal cord procedures (dorsal root entry zone [DREZ] lesion, cordotomy, commissurotomy, ex- tralemniscal myelotomy, commissural myelotomy, and cordectomy), and encephalic/cranial procedures (tri- geminal nucleotomy, bulbar and pontine spinothalamic tractotomy, mesencephalic tractotomy, thalamotomy, hypothalamotomy, cingulotomy, and hypophysectomy). Presently, there are few ablative procedures that can be considered useful in the treatment of specifi c neuro- pathic pain conditions. Th e following is a discussion of some important conditions for which surgical therapies may be indicated:

    Trigeminal Rhizotomy Idiopathic TN refractory to medical therapy is, un- doubtedly, one of the best examples of neuropathic pain for which ablative procedures remain extremely useful, eff ective, and carry very low risk. Percutaneous RF tri- geminal rhizotomy is a remarkably eff ective treatment option, after which most patients are free of pain and can discard the medications they take for this condi- tion. Th e procedure relies on the application of RF elec- tric current to a portion of the trigeminal root, either

    Fig. 1. Coronal magnetic resonance image showing (a) trigeminal neurinoma (arrows), and (b) complete removal after microsurgical resection.

    a b

  • Surgical Treatment for Neuropathic Pain 441

    in or just behind the gasserian ganglion, to generate heat locally in order to destroy some of the nerve fi bers within it, predominantly nociceptive fi bers, because of their greater susceptibility to heat. Th e aim is to achieve a total or almost total analgesia in the cutaneous area that corresponds to the heated portion of the trigeminal root, accompanied by only partial hypoesthesia in the same area.

    Th e approach is essentially the same as that de- scribed by Härtel in 1914 for injection treatments [26]. Under fl uoroscopy guidance, the needle is inserted 2–3 cm lateral to the corner of the mouth on the symptom- atic side of the face and then advanced in a superior, posterior, and medial direction to reach the foramen ovale and the gasserian ganglion while always remain- ing under the mucosa. Once the tip of the needle has passed through the foramen ovale, it is advanced fur- ther until it just overlies the clival line under lateral fl uoroscopic view (Fig. 2). Th e guide needle is removed, and a few drops of cerebrospinal fl uid (CSF) generally emerge from the needle. By this time, a stimulation test is performed to elicit paresthesia in the area of pain. Taha and Tew [88] state that the electrode tip should be

    5 mm beyond the clival line for V1 stimulation, just at the clival line for V2 stimulation, and 5 mm in front of the clival line for V3 stimulation. Once the needle po- sition has been confi rmed, RF lesions are performed, usually at 65°C for 1 minute each. Th e endpoint is the achievement of hypoalgesia or analgesia in the initially painful area, with no more than partial hypoesthesia.

    Gybels and Sweet [24], and more recently Kan- polat et al. [36] evaluated the results of large series that had been published emphasizing that early complete re- lief of pain was obtained in more than 95% of patients in all series. Th e rate of late recurrence requiring reop- eration was generally in the range of 20% to 30%. Dys- esthesia in the treated area is a common postoperative phenomenon (5% to 24% in various series) that some- times requires treatment with medication. Anesthesia dolorosa is defi ned as dysesthesia arising in a totally an- esthetic area and is much more rare (1.2%).

    In addition to RF techniques, other ablative procedures are used to control pain secondary to tri- geminal neuralgia with satisfactory results. In 1971, Lars Leksell published the results of two patients with trigeminal neuralgia treated with his pioneering

    a b

    Fig. 2. Intraoperative fl uoroscopic image during percutaneous trigeminal rhizotomy: (a) lateral view, (b) head-on view of the foramen ovale. ST, sella turcica; CL, clival line; FO, foramen ovale.

  • 442 Fabián C. Piedimonte

    technique of stereotactic radiosurgery in 1953 [42]. Th is technique is now accepted as the least invasive of all sur- gical procedures for the treatment of TN. However, it is more expensive than percutaneous techniques. Results vary among publications; however, it is estimated that approximately 75% of patients are pain free initially, but less than 60% maintain this outcome after 2 years, and just over half of treated patients remain pain free on or off medications at a 3-year follow-up [47].

    In 1981, Sten Hakanson reported the retrogas- serian glycerol rhizolysis technique for treating TN via glycerol injection into the trigeminal cistern, a minimally invasive method with low surgical risk and little impact on facial sensibility [25]. In 1983, Mullan and Lichtor pioneered the concept of percutaneous balloon com- pression for trigeminal neuralgia [51]. Th is procedure is especially useful in patients with fi rst division pai

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