Introduction: Transcranial MR-guided focused ultrasound (FUS) is a novel method for creating thalamic lesions in the treatment of essential tremor. In this procedure, MR thermography is used to verify lesion target and size, allowing precise lesion placement and predictable lesion volume. The objectives of this study are to characterize FUS thalamotomy lesion volume over time and determine if there is a correlation between lesion volume and relief of tremor, or if additional procedural factors improve outcomes.
Methods: This is a retrospective study of 15 patients who underwent stereotactic FUS thalamotomy in a pilot study for treatment of essential tremor at the University of Virginia. MRI scans were obtained at 1 day, 1 week, and 1 month postoperatively. Lesion volumes and diameters were measured on T2-weighted MR images. Procedural details including number of sonications, final power, final energy, and peak voxel temperature were collected retrospectively. Tremor severity was graded by the CRST preoperatively, at the time of MRI, and 1 year postoperatively. Statistical analysis was performed using Wilcoxon rank sum tests, Fisher’s exact tests, and univariate analysis.
Results: FUS lesions can be divided into three zones according to imaging appearance and histological characteristics. Zone 1 corresponds to the area of coagulative necrosis, and zone 3 corresponds to vasogenic edema. Average zone 1 volumes were 248, 338, and 144mm3 at 1-day, 1-week, and 1-month, respectively. Average zone 3 volumes were 1207, 1171, and 186mm3 at the same time-points. There was no statistically significant correlation between treatment conditions, lesion volume, lesion diameter, and tremor relief or transient adverse symptoms.
Conclusions: Effective lesion volumes calculated on T2-weighted imaging on postoperative day #1 ranged from 130-460 mm3. Lesion volumes peaked at 1 week and decreased thereafter. There was no correlation of lesion size with tremor relief.
Patient Care: This study provides important information regarding early imaging characteristics of thermal lesions and the lesion volumes required for effective treatment of tremor. This information is important for future trials using transcranial focused ultrasound for the treatment of movement disorders and other intracranial targets as this method is applied to other disorders.
Learning Objectives: By the conclusion of this session, participants should be able to:
1. Understand possible mechanisms for how transcranial MR-guided focused ultrasound thalamotomy is effective in tremor reduction for patients with essential tremor.
2. Describe the physical and temporal characteristics of thermal lesions produced by transcranial MR-guided focused ultrasound.
3. Identify possible reasons for why lesion volume was not correlated to tremor relief in this study.
References: 1. Montgomery EB. Evaluation of surgery for Parkinson’s disease: Report of the therapeutics and technology assessment subcommittee of the American Academy of Neurology. Neurology 1999;53:1910-21.
2. Zesiewicz TA, Elble R, Louis ED, et al. Practice peramter: Therapties for essential tremor: Report of the quality standards subcommittee of the American Academy of Neurology. Neurology 2005;64:2008-20.
3. Benabid AL, Pollack P, Gao D, et al. Chronic electrical stimulation of the ventralis intermedius nucleus of the thalamus as a treatment of movement disorders. J Neurosurg 1996;84:203-14.
4. Schuurman PR, Bosch DA, Bossuyt PM, et al. A comparison of continuous thalamic stimulation and thalamotomy for suppression of severe tremor. N Engl J Med 2000;342:461-8.
5. Jankovic J, Cardoso F, Grossman RG, et al. Outcome after stereotactic thalamotomy for parkinsonian, essential, and other types of tremor. Neurosurgery 1995;37:680-686.
6. Nagaseki Y, Shibazaki T, Hirai T, et al. Long-term follow-up results of selective VIM-thalamotomy. J Neurosurg 1986;65:296-302.
7. Hirabayashi H, Hariz MI, Wardell K, et al. Impact of parameters of radiofrequency coagulation on volume of stereotactic lesion in pallidotomy and thalamotomy. Stereotact Funct Neurosurg 2012;90:307-15.
8. Hariz MI. Correlation between clinical outcome and size and site of the lesion in computed tomography guided thalamotomy and pallidotomy. Stereotact Funct Neurosurg 1990;54-55:172-85.
9. Hariz MI, Hirabayashi H. Is there a relationship between size and site of the stereotactic lesion and symptomatic results of pallidotomy and thalamotomy? Stereotact Funct Neurosurg 1997;69:28-45.
10. Goodman SH, Wilkinson S, Overman J, et al. Lesion volume and clinical outcome in stereotactic pallidotomy and thalamotomy. Stereotact Funct Neurosurg 1998;71:164-72.
11. Tollefson TT, Burns J, Wilkinson S, et al. Comparative magnetic resonance image-based evaluation of thalamotomy and pallidotomy lesion volumes. Stereotact Funct Neurosurg 1998;71:131-44.
12. Jeanmonod D, Werner B, Morel A, et al. Transcranial magnetic resonance imaging-guided focused ultrasound: noninvasive central lateral thalamotomy for chronic neuropathic pain. Neurosurg Focus 2012;32:E1.
13. Elias WJ, Huss D, Voss T, et al. A pilot study of focused ultrasound thalamotomy for essential tremor. N Engl J Med 2013;369:640-8.
14. Chen L, Bouley D, Yuh E, et al. Study of focused ultrasound tissue damage using MRI and histology. J Magn Reson Imaging 1999;10:146–53.
15. Elias WJ, Khaled M, Hilliard JD, et al. A magnetic resonance imaging, histological, and dose modeling comparison of focused ultrasound, radiofrequenct, and Gamma Knife radiosurgery lesions in swine thalamus. J Neurosurg 2012;119:307-17.
16. Cline HE, Schenck JF, Watkins RD, et al. Magnetic resonance-guided thermal surgery. Magn Reson Med 1993;30:98-106.
17. De Poorter J, De Wagter C, De Deene Y, et al. Noninvasive MRI thermometry with the proton resonance frequency (PRF) method: in vivo results in human muscle. Magn Reson Med 1995;33:74-81.
18. Ishihara Y, Calderon A, Watanabe G, et al. A precise and fast temperature mapping using water proton chemical shift. Magn Reson Med 1995;34:814-23.
19. Moser D, Zadicario E, Schiff G, et al. Measure of targeting accuracy in focused ultrasound functional neurosurgery. Neurosurg Focus 2012;32:E2.
20. Atkinson JD, Collins DL, Bertrand G, et al. Optimal location of thalamotomy lesions for tremor associated with Parkinson disease: a probabilistic analysis based on postoperative magnetic resonance imaging and an integrated digital atlas. J Neurosurg 2002;96:854-66.
21. Hassler R. The influence of stimulations and coagulations in the human thalamus on the tremor at rest and its physiopathologic mechanism. Proceedings of the Second International Congress of Neuropathology 1955:637-42.
22. Hassler R. Architectonic organization of the thalamic nuclei. Stereotaxy of Human Brain 1982:140-80.
23. Tomlinson FH, Jack CR Jr, Kelly PJ. Sequential magnetic resonance imaging following stereotactic radiofrequency ventralis lateralis thalamotomy. J Neurosurg 1991;74:579-84.