Impact of target location on the response of trigeminal neuralgia to stereotactic radiosurgery

Abstract

Object The authors evaluate the impact of target location on the rate of pain relief (PR) in patients with intractable trigeminal neuralgia (TN) undergoing stereotactic radiosurgery (SRS). Methods The authors conducted a retrospective review of 99 patients with idiopathic TN who were identified from a prospectively maintained database and were treated with SRS targeting the dorsal root entry zone with a maximum dose of 80 Gy. Targeting of the more proximal portion of a trigeminal nerve with the 50% isodose line overlapping the brainstem was performed in 36 patients (proximal group). In a matched group, 63 patients received SRS targeting the 20% isodose line tangential to the emergence of the brainstem (distal group). The median follow-up time was 33 months (range 6–124 months). Results The actuarial rate of maintenance of Barrow Neurological Institute (BNI) Pain Score I–IIIa was attained in 89% of patients at 1 year, 81% at 2 years, and 69% at 4 years, respectively, after SRS. Kaplan-Meier analysis revealed that durability of PR was only associated with the proximal location of the radiosurgical target (log-rank test, p = 0.018). Radiosurgery-induced facial numbness (BNI Score II or III) developed in 35 patients, which was significantly more frequent in the proximal group (19 patients [53%] compared with 16 [25%] in the distal group [p = 0.015]). Conclusions The radiosurgical target appears to affect the duration of pain relief in patients with idiopathic trigeminal neuralgia with the target closer to the brainstem affording extended pain relief. However, the proximal SRS target was also associated with an increased risk of mild to moderate facial numbness.

Long-term safety and efficacy of Gamma Knife surgery in classical trigeminal neuralgia: a 497-patient historical cohort study

“…8 Also, a target placed close to the brainstem at the level of the root entry zone 26 seems to be associated with a higher risk of numbness and higher risk of bothersome hypesthesia. This fact is confirmed by the recent paper by Sheehan et al 42 who found more numbness in a group of patients where the target used was the so-called dorsal root entry zone in comparison with the more anterior cisternal target that the authors used later on in their series. The major impact of these technical nuances may explain the large variability in the safety and efficacy reported in the literature.…”

Advances in diagnosis and treatment of trigeminal neuralgia

“…In a recent study, the radiosurgical target appeared to affect the duration of pain relief with the target closer to the brainstem, providing extended pain relief. However, the proximal radiosurgical target was also associated with an increased risk of mild to moderate facial numbness 123. Alternative targets include the trigeminal nuclei in the brainstem or the centromedian nucleus of the thalamus 124.…”

A successful case of multiple stereotactic radiosurgeries for ipsilateral recurrent trigeminal neuralgia

“…5,16,28 The belief behind targeting the root entry zone is that this area involves a transition zone in the axons from peripheral to central myelin, which in theory is believed to be more susceptible to radiation. 33 Several articles have documented histopathological evidence of axonal degeneration and fibrosis after GKRS.…”

“…During the patient's 5-, 113-, and 36-month pain-free durations after each GKRS, his Barrow Neurological Institute (BNI) Facial Hypesthesia Scale score was never above II, as he had mild facial numbness that was not bothersome. 33 A table describing both the latency until pain relief after each surgical and GKRS procedure, as well as the duration of pain relief achieved for each of these procedures, can be seen in Table 1.…”