Gamma knife surgery for idiopathic trigeminal neuralgia performed using a far-anterior cisternal target and a high dose of radiation

Abstract

To optimize pain control and minimize complications of this therapy, we recommend that the nerve be targeted at a distance of 5 to 8 mm from the brainstem.

Gamma Knife stereotactic radiosurgical treatment of idiopathic trigeminal neuralgia: long-term outcome and complications

“…Our excellent and good outcome rates are comparable to those reported in previously published studies. 6,8,17,19,23 The observed excellent and good outcome rates in our patients as well as those of other large studies published in the last decade are summarized in Table 2.…”

“…8,16 Numerous authors have reported on SRS with the GK, and outcome and complication rates have been variable. [1][2][3][4][5][6]8,[10][11][12][13][14][15][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] The observed variation in success rates in the literature may be explained by the subjectivity of assessing pain (which is the most important outcome parameter in these studies), the multifactorial causes of TN (idiopathic or secondary to a pathological entity), the significantly varying stereotactic radiosurgical treatment protocols (different anatomical targets and different radiation doses), and the usage of illdefined and widely variable outcome assessment criteria.…”

“…This finding may indicate that patients with no previous surgeries not only respond better to SRS treatment but maintain their excellent or good response longer than patients with a history of previous surgery; this parameter should be seriously considered in the surgical planning for SRS. Régis and colleagues 24,25 and Massager et al 19 have suggested that using a higher radiation dose and targeting the distal portion of the trigeminal root immediately posterior to the gasserian ganglion may improve outcome in patients with idiopathic TN who have had multiple previous surgeries.…”

“…1,3,13,17,28,29 It must be emphasized that the actual delivered dose might be different from the prescribed maximal dose from one GK unit to another due to variations in the output factor for the 4-mm collimator, 0.8-0.85, depending on the institution and medical physics techniques used to measure the output factor. 19 In addition, several other parameters such as advanced patient age, the presence of concomitant vasculopathy, systemic diseases such as multiple sclerosis, a small trigeminal cistern, and/or a history of previous radiosurgical treatments may lead to the use of a lower radiation dose. 41 Massager et al 20 have emphasized the fact that the radiobiological effect of GKS may be related to the energy delivered to the trigeminal nerve root volume, rather than the maximal radiation dose delivered.…”

“…20 In a recent study, Massager and colleagues,20 demonstrated that the incidence of trigeminal nerve dysfunction is significantly related to the prescription dose and the usage of shielding. Interestingly, Massager et al, 19 in another series, reported only 4% posttreatment incidence of facial numbness in a cohort of patients treated with 90-Gy maximal prescription dose. The incidence of facial numbness in their study is significantly lower that that observed in ours, although our maximal radiation doses were lower than theirs.…”