Journal of Dr. NTR University of Health Sciences

REVIEW ARTICLE
Year
: 2016  |  Volume : 5  |  Issue : 3  |  Page : 169--172

Gamma knife radiosurgery: Making lives merrier for refractory trigeminal neuralgia


Raj Kumar Badam1, Supraja Chowdary1, Sudheer Kanth Kondamari2, Sujan Kumar Kotha3,  
1 Department of Oral Medicine and Radiology, Panineeya Mahavidyalaya Institute of Dental Sciences and Research Centre, Hyderabad, India
2 Department of Oral and Maxillofacial Pathology, Mamatha Dental College, Khammam, Telangana, India
3 Department of Orthodontics, MNR Dental College, Sangareddy, Telangana, India

Correspondence Address:
Raj Kumar Badam
Department of Oral Medicine and Radiology, Panineeya Mahavidyalaya Institute of Dental Sciences and Research Centre, Kamala Nagar, Dilshuk Nagar, Hyderabad - 500 018, Telangana
India

Abstract

Trigeminal neuralgia (TN), also known as tic Dolorex, is a unilateral paroxysmal lancinating pain affecting one or more of the branches of the trigeminal nerve. The treatment of TN can be very challenging despite the numerous options patients and physicians can choose from. Stereotactic radiosurgery (SR) with gamma knife surgery (GKS) is a rapidly emerging surgical modality in the management of medically refractory TN. GKS is the most recent and least invasive neurosurgical treatment alternative to microvascular decompression and rhizotomies. The gamma knife is a complex machine that uses cobalt-60 as energy and is able to focus a precise intersection of 201 beams of these gamma rays to perform radiosurgery. It is associated with a low risk of facial paresthesia, an approximately 80% rate of significant pain relief, and a low recurrence rate.



How to cite this article:
Badam RK, Chowdary S, Kondamari SK, Kotha SK. Gamma knife radiosurgery: Making lives merrier for refractory trigeminal neuralgia.J NTR Univ Health Sci 2016;5:169-172


How to cite this URL:
Badam RK, Chowdary S, Kondamari SK, Kotha SK. Gamma knife radiosurgery: Making lives merrier for refractory trigeminal neuralgia. J NTR Univ Health Sci [serial online] 2016 [cited 2019 Nov 19 ];5:169-172
Available from: http://www.jdrntruhs.org/text.asp?2016/5/3/169/191852


Full Text

 Introduction



Trigeminal neuralgia (TN) is defined as “unilateral disorder characterized by brief electric shock like pain, abrupt in onset and termination, and limited to the distribution of one or more divisions of the trigeminal nerve.”[1] The overall incidence is estimated to be approximately four to five cases per year per 1,00,000 people and increases with age.[2] TN can be caused by tumors involving the trigeminal nerve, ganglion, or divisions as well as by demyelinating plaques in the dorsal nerve root entry zone, descending trigeminal tracts, or brainstem nuclei due to multiple sclerosis (MS). However, most patients suffer from nonneoplastic TN that is thought to arise from vascular compression and focal demyelination of the trigeminal root, leading to excitability of nerve fibers.[3]

The treatment of TN can be very challenging despite the numerous options patients and physicians can choose from. This multitude of treatment options poses questions as to which treatment fits which patient best.

In most patients, the pain is initially managed pharmacologically with anticonvulsant or antidepressant medications. However, both classes of medications are associated with a wide variety of side effects, including sedation, impaired memory, peripheral neuropathy, confusion, tremors, nausea, and insomnia.

Several surgical options are available for patients with medically retractable TN. Surgical management of TN consists of nonablative and ablative treatments. Microvascular decompression (MVD), the only nonablative technique for TN due to vascular compression of the trigeminal nerve, provides the best rates of long-term complete pain relief and preservation of facial sensation. However, it requires neurosurgery of the posterior fossa and is associated with serious morbidity and mortality, including the risks of hearing loss, sensory loss, cerebrospinal fluid leakage, and 1% death rate.[4] Many patients with TN are elderly, have medical contraindications, or do not wish to undergo traditional open surgery. Ablative techniques damage the trigeminal nerve at specific sites and include radiofrequency thermocoagulation, glycerol rhizolysis, balloon compression, or posterior fossa partial sensory rhizotomy. Ablative techniques are typically minimally invasive, require short hospital stays, and provide immediate relief of pain in most patients. However, these modalities have comparatively high rates of facial sensory loss or trigeminal motor dysfunction; pain often recurs in several years, and they incur a rare but devastating risk of anesthesia dolorosa.

Stereotactic radiosurgery (SR) with gamma knife surgery (GKS) is an established treatment option for medically refractory TN. Stereotactic irradiation of the trigeminal ganglion was first reported by Leksell in 1951. This ablative procedure is the only minimally invasive technique modifying the trigeminal pathway at the same site as modern microsurgery.

 Stereotactic Radiosurgery



Radiosurgery is a procedure, which allows noninvasive brain surgery and is used to destroy intracranial tumors and other lesions that could be otherwise inaccessible or inadequate for open surgery by means of a precise dosage of radiation.

SR is defined as “the stereotactic (precision) delivery of multiple cross-fired radiation beams to a point or volume within a configured space.”[5]

History of gamma knife

Radiosurgery was first developed at the Karolinska Institute of Stockholm, Sweden in 1949. It was later jointly modified by Dr. Lars Leksell, a neurosurgeon and Bjorn Larsson, a radiobiologist from Uppsala University. Leksell initially used protons from a cyclotron to irradiate brain tumor lesions. In 1968, they developed the gamma knife, a new device exclusively for radiosurgery, which consisted of radioactive sources of Cobalt-60 placed in a kind of helmet with central channels for irradiation, using gamma rays. In the latest version of this device, 192 sources of radioactive cobalt direct gamma radiation to the center of a helmet, where the patient's head is inserted. This is called the Leksell Gamma Knife Perfexion [Figure 1]. Gamma knife radiosurgery has proven effective for patients with benign or malignant brain tumors up to 4 cm in size, TN, vascular malformations such as an arteriovenous malformation (AVM), pain, or other functional problems.{Figure 1}

Gamma knife

Gamma knife, the prototype of SR involves the “center of arc” principle in which the center of the target is the center of the circular arc rotation. 201 cobalt gamma ray beam sources are arrayed in a hemisphere and aimed through a collimator to a common focal point. The patient's head is positioned within the gamma knife so that the tumor is in the focal point of the gamma rays [Figure 2]. The cross section view of the gamma knife shows the large shielding ball, which contains radioactive cobalt pellets that provide the radiation delivered by the gamma knife [Figure 3]. The total weight of the gamma knife ball alone is approximately 44,000 pounds.{Figure 2}{Figure 3}

Gamma radiation is used in the “Gamma knife” device where they are produced by fixed sources of radioactive cobalt. Cobalt has been chosen for its reliability and beam stability, with a half-life of 5 years. The helmet is critical as it holds the collimators, which shape the beams of radiation. Radiation would pass through these ports in the helmet into the brain, converging on the target. The helmet has circular collimators of 4 mm, 8 mm, 14 mm, and 18 mm. They will shape the beams and block out all but a small portion of the individual beams of the gamma knife, which allows the surgery to be as accurate as possible.

Planning protocols for gamma knife procedures include positioning of the patient into the head frame [6] diagnostic imaging of a computed tomography or magnetic resonance imaging for treatment planning, using the information obtained from diagnostic imaging; gamma knife computerized treatment planning software develops a 3-dimensional picture of the target lesion and surrounding tissue and radiation dose, and delivery is planned by placing one or more isocenters. Each isocenter represents a point at which all of the beams converge for a certain amount of time. Optimal radiation dose in SR of TN remains debatable; however, the maximum dose is in the range of 70-90 Gy to the target area.[7],[8],[9] When planning is complete, the patient is placed in a supine position on the gamma knife table and the head frame is fixed to the unit. The position of the head frame is adjusted with a series of dials such that the target is at the center of the beam, as defined by the plan. The patient is then monitored from outside the room while treatment is given, usually 30-90 min. Most patients are treated on an outpatient basis.

 Mechanism of Action of Gamma Knife Surgery



The exact mechanism of pain relief is unknown. However, it is thought to be a two-step process, one being immediate interruption of emphatic transmission leading to an immediate decrease in the intensity of the pain even if the attacks still occur. Several weeks later, there is complete cessation of the attacks. This is probably secondary to delayed demyelination injury to the nerve.[10] The advantages of gamma knife surgery are it is a bloodless brisk procedure eliminating the risk of infection and with no potential disfigurements, virtually painless, requires no general anesthesia with predictable outcome, and is economical with 20% less than conventional neurosurgery.[11] Complications include facial numbness, facial paresthesia, and less commonly reported complications included troublesome dysesthesia, loss of taste, corneal numbness, and deafness.[12]

 Conclusion



The revolution of sophisticated software and computer technology combined with advanced radiation physics has produced a new tool, gamma knife for the successful treatment of TN. It not only relieves pain when compared to other neurosurgical forms but does so with fewer complications. Durability and low complication rate make gamma knife surgery an acceptable treatment modality.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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