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Pain


Table 1: A Modified Burchiel Facial Pain Classification System


Diagnosis


Idiopathic Type 1 trigeminal neuralgia Type 2 trigeminal neuralgia


Trigeminal injury Deafferentation pain


Multiple sclerosis trigeminal neuralgia Post-herpetic neuralgia


Other Atypical facial pain


Description


>50 % episodic pain >50 % constant pain


Secondary to unintentional or intentional nerve injury


Demyelination of trigeminal system Following herpes zoster outbreak


Somatoform facial pain disorder


demyelination, and are analogous to phantom limb pain. The etiologies of typical tic douloureux include vascular cross-compression as well as demyelinating events in the context of MS. The various etiologies require different treatment options. Depending on the pain syndrome, various treatment strategies may work well for some, but not all patients.


Treatment Options for Trigeminal Neuralgia The first-line management for TN is medical therapy. Typical initial oral agents include carbamazepine, oxcarbazepine, gabapentin, phenytoin, and baclofen, used alone or in combination. The effectiveness of medications typically wanes over time despite increasing doses, with many patients not able to tolerate side effects.8


Eventually, as many as


50 % of TN patients can be labeled as medically refractory and require alternative management for pain relief.9


Surgical treatment options for


TN fit on a spectrum of invasiveness and risk from MVD (most invasive, highest risk) to gamma knife radiosurgery (GKRS) (least invasive, lowest risk). Treatment of these medically refractory patients needs to be tailored with consideration given to patient age, medical comorbidities, severity of symptoms, and personal preference.


The goal of surgical management of TN is to achieve pain control and yet minimize risks. Surgeons must balance surgical risks, preservation of trigeminal sensation, and hopefully eliminate the need for continued medication use. The first successful open surgical therapy for TN involved sectioning the trigeminal nerve at one of a number of locations, the most popular and successful approach being the subtemporal approach for retrogasserian neurectomy.10


Walter Dandy is first credited with suggesting


that vascular compression of the trigeminal nerve was the etiology of TN.11 However, it was Peter Jannetta, with the use of the operating microscope, who demonstrated the utility of vascular decompression.3


Although not


initially meeting with widespread acceptance, the long-term success of MVD has led to it becoming the treatment of choice if a craniotomy is feasible. In a large surgical series, 80 % of patients experienced complete pain relief immediately after MVD, with nearly another 10 % having partial relief.4


Gamma Knife Radiosurgery for Trigeminal Neuralgia Since the development of the gamma knife in the 1960s by Leksell and Larsson, the technology has evolved tremendously. All gamma knife instruments are based on the same fundamental principle: closed-cranial irradiation of intracranial targets using multiple photon beams after localization of the target(s) in stereotactic space.18


Each unit possesses


These results have proved durable: at one year, 75 % of patients report excellent results (defined as 98 % decrease in pain and off medications) with another 9 % reporting a good outcome (a 75 % decrease in pain and on low-dose medication). At 10 years, 64 % continued to have excellent outcomes, while 4 % had good outcomes. However, the major complication rate following MVD was around 8 %, including permanent neurological deficit, cerebrospinal fluid leak, bacterial meningitis, and death. Thus, although MVD is a highly effective therapy and patients often


150


either 192 or 201 radioactive cobalt-60 sources that are spherically arrayed via collimator helmets to focus their beams to a center point. The procedure begins with application of a stereotactic frame to the head. Treatment planning images are then obtained, typically by magnetic resonance imaging (MRI) or, if contraindicated, computed tomography (CT). Finally, the actual treatment consists of the patient lying on a couch with his or her head in the stereotactic frame rigidly attached to the instrument. The patient is then placed in the focus of the chosen beams which converge on the target.


US NEUROLOGY


respond immediately, it has associated risks that relate in part to the experience and skill of the surgeon who performs the procedure. Unfortunately, due to advanced age or medical comorbidities, not all patients are candidates for MVD.12


For patients who are unable or unwilling to tolerate the risks associated with MVD, several different percutaneous rhizotomy procedures are available. The first percutaneous therapy directed at the gasserian ganglion is credited to Harris in 1910.13


These first procedures involved the


injection of alcohol into the ganglion and were successful in producing pain relief but at the expense of often profound anesthesia of the face and resultant deafferentation pain in some patients. Recurrences of TN were treated by additional injections when necessary.13


Unfortunately, this


early technique was associated with other potential morbidity, including spread of the alcohol within the cerebrospinal fluid and resultant damage to other cranial nerves. This type of procedure evolved further when Häkanson inadvertently discovered that injection of glycerol, a much weaker neurolytic alcohol, produced symptomatic relief of TN.14


Specifically, glycerol is confined to the trigeminal cistern by actually measuring the cistern volume using non-ionic contrast media to perform cisternography.


Other techniques that use a transfacial percutaneous approach to the trigeminal cistern include radiofrequency rhizotomy and balloon microcompression. In our experience at the University of Pittsburgh, 1,174 patients underwent percutaneous retrogasserian glycerol rhizotomy. Ninety per cent of patients achieved early complete pain relief.15


With


longer-term follow-up out to 11 years, persistent pain control was achieved in 77 % of patients; 55 % were able to eliminate medication and 22 % had pain control but still required some medicine.16 al. treated 1,600 TN patients with radiofrequency rhizotomy.17


Kanpolat et After five


years, 58 % were pain-free and 42 % had recurred pain. At 20-year follow-up, 41 % of patients remained pain-free. The advantage of the percutaneous techniques is that they possess intrinsically less surgical risk, offer immediate or near-immediate pain relief, and are repeatable. However, there are patients who are not candidates, including those with medical conditions requiring long-term anticoagulation or antiplatelet agents. Percutaneous radiofrequency rhizotomy is also associated with the risk of a diminished corneal reflex, masseter weakness, anesthesia dolorosa, aseptic meningitis, and herpes simplex reactivation.


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