Книги по МРТ КТ на английском языке / Neurosurgery Fundamentals Agarval 1 ed 2019

[42]Racusin DA, Villarreal S, Antony KM, et al. Role of maternal serum alpha-fetoprotein and ultrasonog- raphy in contemporary detection of spina bifida.

Am J Perinatol. 2015; 32(14):1287–1291

[43]Birnbacher R, Messerschmidt AM, Pollak AP. Diagnosis and prevention of neural tube defects. Curr Opin Urol. 2002; 12(6):461–464

[44]Kumar R, Bansal KK, Chhabra DK. Occurrence of split cord malformation in meningomyelocele: complex spina bifida. Pediatr Neurosurg. 2002;

36(3):119–127

[45]Cowchock S, Ainbender E, Prescott G, et al. The recurrence risk for neural tube defects in the United States: a collaborative study. Am J Med Genet. 1980; 5(3):309–314

[46]Seller MJ. Recurrence risks for neural tube defects in a genetic counseling clinic population. J Med Genet. 1981; 18(4):245–248

[47]Czeizel A, Métneki J. Recurrence risk after neural tube defects in a genetic counselling clinic. J Med Genet. 1984; 21(6):413–416

[48]Sarmah S, Muralidharan P, Marrs JA. Common congenital anomalies: Environmental causes and prevention with folic acid containing multivitamins. Birth Defects Res C Embryo Today. 2016; 108(3):274–286

[49]Viswanathan M, Treiman KA, Kish-Doto J, Middleton JC, Coker-Schwimmer EJ, Nicholson WK. Folic acid supplementation for the prevention of neural tube defects: an updated evidence report and systematic review for the US Preventive Services Task Force. JAMA. 2017; 317(2):190–203

[50]De-Regil LM, Peña-Rosas JP, Fernández-Gaxiola

AC, Rayco-Solon P. Effects and safety of pericon- ceptional oral folate supplementation for preventing birth defects. Cochrane Database Syst Rev. 2015(12):CD007950

[51]Atta CA, Fiest KM, Frolkis AD, et al. Global birth prevalence of spina bifida by folic acid fortification status: a systematic review and meta-analysis. Am J Public Health. 2016; 106(1):e24–e34

[52]Tinker SC, Cogswell ME, Devine O, Berry RJ. Folic acid intake among U.S. women aged 15–44 years, National Health and Nutrition Examination Survey, 2003–2006. Am J Prev Med. 2010; 38(5):534–542

[53]Sadler TW. Langman’s Medical Embryology. Philadelphia, PA: Lippincott Williams & Wilkins; 2011

[54]Stone DH. The declining prevalence of anencepha- lus and spina bifida: its nature, causes and implica- tions. Dev Med Child Neurol. 1987; 29(4):541–546

[55]Mathews TJ, Honein MA, Erickson JD. Spina bifida and anencephaly prevalence—United States, 1991– 2001. MMWR Recomm Rep. 2002; 51(RR-13):9–11

[56]Kiymaz N, Yilmaz N, Demir I, Keskin S. Prognostic factors in patients with occipital encephalocele. Pediatr Neurosurg. 2010; 46(1):6–11

[57]Hubballah MY, Hoffman HJ. Early repair of my- elomeningocele and simultaneous insertion of ventriculoperitoneal shunt: technique and results. Neurosurgery. 1987; 20(1):21–23

[58]Sutton LN. Fetal surgery for neural tube defects. Best Pract Res Clin Obstet Gynaecol. 2008; 22(1):175–188

[59]Cools MJ, Al-Holou WN, Stetler WR, Jr, et al. Filum terminale lipomas: imaging prevalence, natural history, and conus position. J Neurosurg Pediatr. 2014; 13(5):559–567

[60]Tortori-Donati P, Rossi A, Cama A. Spinal dysraphism: a review of neuroradiological features with embryological correlations and proposal for a new classification. Neuroradiology. 2000; 42(7):

471–491

[61]Drake JM. Occult tethered cord syndrome: not an indication for surgery. J Neurosurg. 2006; 104(s)(uppl)( 5):305–308

[62]Yamada S, Won DJ, Siddiqi J, Yamada SM. Tethered cord syndrome: overview of diagnosis and treatment. Neurol Res. 2004; 26(7):719–721

[63]Cardoso M, Keating RF. Neurosurgical management of spinal dysraphism and neurogenic scoliosis. Spine. 2009; 34(17):1775–1782

[64]Schijman E. Split spinal cord malformations: report of 22 cases and review of the literature. Childs Nerv Syst. 2003; 19(2):96–103

[65]Bruce DA, Schut L. Spinal lipomas in infancy and childhood. Childs Brain. 1979; 5(3):192–203

[66]Pretorius DH, Russ PD, Rumack CM, Manco-Johnson ML. Diagnosis of brain neuropathology in utero. Neuroradiology. 1986; 28(5–6):386–397

[67]Greene MF, Benacerraf B, Crawford JM. Hydranencephaly: US appearance during in utero evolution. Radiology. 1985; 156(3):779–780

[68]Shitsama S, Wittayanakorn N, Okechi H, Albright AL. Choroid plexus coagulation in infants with extreme hydrocephalus or hydranencephaly. J Neurosurg Pediatr. 2014; 14(1):55–57

[69]Kaliaperumal C, Ndoro S, Mandiwanza T, et al. Holoprosencephaly: antenatal and postnatal diagnosis and outcome. Childs Nerv Syst. 2016; 32(5):801–809

[70]Demyer W, Zeman W, Palmer CG. The face predicts the brain: diagnostic significance of median facial anomalies for holoprosencephaly (arhinencephaly). Pediatrics. 1964; 34(2):256–263

[71]Guibaud L, Larroque A, Ville D, et al. Prenatal diagnosis of ‘isolated’ Dandy-Walker malformation: imaging findings and prenatal counselling. Prenat

Diagn. 2012; 32(2):185–193

[72]Nyberg DA, Cyr DR, Mack LA, Fitzsimmons J, Hickok D, Mahony BS. The Dandy-Walker malformation prenatal sonographic diagnosis and its clinical sig- nificance. J Ultrasound Med. 1988; 7(2):65–71

[73]Taylor GA, Sanders RC. Dandy-Walker syndrome: recognition by sonography. AJNR Am J Neuroradiol. 1983; 4(6):1203–1206

[74]Kirkinen P, Jouppila P, Valkeakari T, Saukkonen AL. Ultrasonic evaluation of the Dandy-Walker syndrome. Obstet Gynecol. 1982; 59(s)(uppl)( 6): 18–21

[75]Bromley B, Nadel AS, Pauker S, Estroff JA, Benac- erraf BR. Closure of the cerebellar vermis: evaluation with second trimester US. Radiology. 1994; 193(3):761–763

[76]Jahangiri A, Molinaro AM, Tarapore PE, et al. Rathke cleft cysts in pediatric patients: presentation, surgical management, and postoperative outcomes. Neurosurg Focus. 2011; 31(1):E3

289

[77]Trifanescu R, Ansorge O, Wass JA, Grossman AB, Karavitaki N. Rathke’s cleft cysts. Clin Endocrinol (Oxf). 2012; 76(2):151–160

[78]Culver SA, Grober Y, Ornan DA, et al. A case for conservative management: characterizing the natural history of radiographically diagnosed Rathke cleft cysts. J Clin Endocrinol Metab. 2015; 100(10):3943–3948

[79]Garrè ML, Cama A. Craniopharyngioma: modern concepts in pathogenesis and treatment. Curr Opin Pediatr. 2007; 19(4):471–479

[80]Lober RM, Harsh GR, IV. A perspective on craniopharyngioma. World Neurosurg. 2013; 79(5–6): 645–646

[81]Tracy MR, Dormans JP, Kusumi K. Klippel-Feil syndrome: clinical features and current understanding of etiology. Clin Orthop Relat Res. 2004(424):183– 190

[82]Citow JS, Macdonald RL, Refai D. Comprehensive Neurosurgery Board Review. New York, NY: Thieme Medical Publishers, Inc.; 2010

[83]Heller J, Klekamp J, Blechner M. Posterior cervical instrumentation. Surgery of the Cervical Spine. Philadelphia, PA: WB Saunders; 2003:52–75

[84]Langensiepen S, Semler O, Sobottke R, et al. Measuring procedures to determine the Cobb angle in idiopathic scoliosis: a systematic review. Eur Spine J. 2013; 22(11):2360–2371

[85]Cobb JR. Outline for the study of scoliosis. Instr Course Lect. 1948; 5:261–275

[86]Kim DH, Betz RR, Huhn SL, Newton PO. Surgery of the Pediatric Spine. New York, NY: Thieme Medical Publishers, Inc.; 2008

[87]Konieczny MR, Senyurt H, Krauspe R. Epidemiology of adolescent idiopathic scoliosis. J Child Orthop. 2013; 7(1):3–9

[88]Fairbank J. Historical perspective: William Adams, the forward bending test, and the spine of Gideon Algernon Mantell. Spine. 2004; 29(17):1953–1955

[89]Altaf F, Gibson A, Dannawi Z, Noordeen H. Adolescent idiopathic scoliosis. BMJ. 2013; 346:f2508

[90]Zhu Z, Wu T, Zhou S, et al. Prediction of curve progression after posterior fossa decompression in pediatric patients with scoliosis secondary to Chiari malformation. Spine Deform. 2013; 1(1):25–32

[91]Jankowski PP, Bastrom T, Ciacci JD, Yaszay B, Levy ML, Newton PO. Intraspinal pathology associated with pediatric scoliosis: a ten-year review analyz- ing the effect of neurosurgery on scoliosis curve progression. Spine. 2016; 41(20):1600–1605

[92]Ramirez N, Johnston CE, Browne RH. The prevalence of back pain in children who have idiopathic scoliosis. J Bone Joint Surg Am. 1997; 79(3):364– 368

[93]Lonstein JE, Carlson JM. The prediction of curve progression in untreated idiopathic scoliosis during growth. J Bone Joint Surg Am. 1984; 66(7):1061– 1071

[94]Weinstein SL, Dolan LA, Cheng JC, Danielsson A, Morcuende JA. Adolescent idiopathic scoliosis. Lancet. 2008; 371(9623):1527–1537

[96]Tomei KL. The evolution of cerebrospinal fluid shunts: advances in technology and technique. Pediatr Neurosurg. 2017; 52(6):369–380

[97]Khan F, Rehman A, Shamim MS, Bari ME. Factors affecting ventriculoperitoneal shunt survival in adult patients. Surg Neurol Int. 2015; 6:25

[98]Khan F, Shamim MS, Rehman A, Bari ME. Analysis of factors affecting ventriculoperitoneal shunt sur- vival in pediatric patients. Childs Nerv Syst. 2013; 29(5):791–802

[99]Bir SC, Konar S, Maiti TK, Kalakoti P, Bollam P, Nanda A. Outcome of ventriculoperitoneal shunt and predictors of shunt revision in infants with posthemorrhagic hydrocephalus. Childs Nerv Syst. 2016; 32(8):1405–1414

[100]Walker CT, Stone JJ, Jacobson M, Phillips V, Silberstein HJ. Indications for pediatric external ventricular drain placement and risk factors for conversion to a ventriculoperitoneal shunt. Pediatr Neurosurg. 2012; 48(6):342–347

[101]Warf BC. Comparison of endoscopic third ventriculostomy alone and combined with choroid plexus cauterization in infants younger than 1 year of age: a prospective study in 550 African children. J Neurosurg. 2005; 103(s)(uppl)( 6):475–481

[102]Singh I, Rohilla S, Siddiqui SA, Kumar P. Growing skull fractures: guidelines for early diagnosis and surgical management. Childs Nerv Syst. 2016; 32(6):1117–1122

[103]Ersahin Y, Gülmen V, Palali I, Mutluer S. Growing skull fractures (craniocerebral erosion). Neurosurg Rev. 2000; 23(3):139–144

[104]Prasad GL, Gupta DK, Mahapatra AK, Borkar SA, Sharma BS. Surgical results of growing skull fractures in children: a single centre study of 43 cases. Childs Nerv Syst. 2015; 31(2):269–277

[105]Ramamurthi B, Kalyanaraman S. Rationale for surgery in growing fractures of the skull. J Neurosurg. 1970; 32(4):427–430

[106]Zegers B, Jira P, Willemsen M, Grotenhuis J. The growing skull fracture, a rare complication of paediatric head injury. Eur J Pediatr. 2003; 162(7–8): 556–557

[107]Muhonen MG, Piper JG, Menezes AH. Pathogenesis and treatment of growing skull fractures. Surg Neurol. 1995; 43(4):367–372, discussion 372–373

[108]de P Djientcheu V, Njamnshi AK, Ongolo-Zogo P, et al. Growing skull fractures. Childs Nerv Syst. 2006; 22(7):721–725

[109]Choudhri AF. Pediatric Neuroradiology: Clinical Practice Essentials. New York, NY: Thieme Medical Publishers, Inc.; 2017

[110]Cirak B, Ziegfeld S, Knight VM, Chang D, Avellino AM, Paidas CN. Spinal injuries in children. J Pediatr Surg. 2004; 39(4):607–612

[111]Baker C, Kadish H, Schunk JE. Evaluation of pediatric cervical spine injuries. Am J Emerg Med. 1999; 17(3):230–234

15.1  Movement Disorders

15.1.1  Parkinson’s Disease Diagnosis

Parkinson’s disease (PD) is the second most common progressive neurodegenerative disease characterized by motor and nonmotor features affecting 2 to 3% of the population older than 65 years,1,​2 with men more likely than women. It is the most common and well-understood disorder of the basal ganglia ( Fig. 15.1).

PD is clinically defined by the presence of bradykinesia, and at least one additional cardinal feature and additional supporting/ exclusion­ criteria. PD can display both motor and nonmotor symptoms.

Motors symptoms are numerous and ­include, but are not limited to, tremor, ­rigidity, akinesia/bradykinesia, postural ­instability, shuffling gait, micrographia, and masked facies. Resting tremor is the most common and easily recognized feature characterized as a “pill-rolling” tremor most prominent in the distal extremities. Rigidity is associated with a “cogwheel phenomenon” when performing a passive movement of the limb.1,​2 Nonmotor symptoms include cognitive impairment, depression, apathy, fatigue, dysautonomia, and sleep disorders.

The National Institute of Neurological Disorders and Stroke (NINDS) diagnostic criteria for PD are as follows:

•Group A features (characteristic): Resting tremor, bradykinesia, rigidity, asymmetric onset.

•Group B features (suggestive of alternate diagnosis): Prominent postural instability,­ freezing phenomenon, or

Fig. 15.1  Coronal section highlighting key structures involved in movement disorder pathophysiologies and treatments. (Reproduced from Kanekar S, Imaging of Neurodegenerative Disorders, ©2015, Thieme Publishers, New York.)3

hallucinations unrelated to medication in the first 3 years; dementia preceding motor symptoms in the first year; supranuclear gaze palsy, slow vertical saccades, or severe dysautonomia.

•Definite PD: All Group A and pathologic confirmation.

•Probably PD: At least four Group A, none group B, and substantial and sustained response to levodopa.

•Possible PD: At least two group A including tremor or bradykinesia, and none group B or symptoms less than 3 years and no features of group B, and substantial and sustained response to levodopa or no adequate trial of levodopa.

Error rates for clinical diagnosis can be as high as 24% which include multiple systems atrophy (MSA), progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), essential tremor (ET), drug-induced parkinsonism, and vascular parkinsonism.

Pathophysiology

PD is hypothesized to be a disease of the basal ganglia, with dopaminergic neuronal loss in the substantia nigra (SN) and intracellular protein accumulation

(α-synuclein) known as Lewy bodies.2

Multiple mutations including PARKIN, PINK, LRRK2, and SCNA have been associated with approximately 20% of cases.4 Net loss of dopaminergic input (> 70% dopaminergic neuronal in the SN) causes opposing effects within the motor striatum with increased activity in the indirect pathway by net disinhibition of the globus pallidus interna (GPi) and subthalamic nucleus (STN), decreased activity of the direct pathway, and net tonic ­gamma-aminobutyric acid-ergic (GABAergic) inhibition of thalamic output to the cortex.

292

Overall, the STN and GPi are noted to be overactive and as such have been the target of ablative treatments, for example, pallidotomy, and deep brain stimulation (DBS) ( Fig. 15.2).2,​4,​5,​6

Treatment

Medical Therapy

The mainstay of pharmacologic treatment for PD involves dopaminergic targets; that is, given loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) leading to dopamine depletion in the striatum as the core mechanism for motor symptoms in PD.

L-Dopa is a precursor of dopamine and was introduced in the1960s and is the gold standard for PD and parkinsonism.5,​6

Patients eventually develop resistance to

L-dopa therapy and develop motor response oscillations and drug-induced dyskinesias. Common preparations including enzyme inhibitors, for example, carbidopa, that prevents peripheral metabolism of dopamine; monoamine oxidase (MAO) inhibitors, for example, selegiline, to inhibit a major postsynaptic clearance mechanisms of dopamine and dopamine agonists on striatum, for example, ropinirole, serve as adjunct therapy given their long half-life.2 Dyskinesia isamajorsideeffectofL-dopawithamanta- dine currently used for treatment of such.

Surgical Therapy

•Deep Brain Stimulation (DBS): The ideal DBS patient is a generally­ healthy patient, with no significant psychiatric disorder, who is levodopa responsive, and

an idiopathic­ PD patient with disabling symptoms and/or significant side effects such as on/off fluctuations.7

DBS involves placement of deep subcortical electrodes into the STN or GPi using stereotactic techniques, with or without intraoperative electrophysiologic monitoring, and which are connected to an implantable pulse generator (IPG) ( Fig. 15.3).

Both demonstrate comparable efficacy in addressing the cardinal motor symptoms (tremor, bradykinesia, gait, rigidity) of PD; reduced off time, on/off fluctuations, and on-medication time dyskinesias; and less marked on-medi- cation state.7,​8

STN over GPi is currently the preferred target based on evidence noting greater reduction of medication requirements (> 50% at 12 months) and lower stimulation voltage, yet with more notable cognitive­ and behavioral side effects.

Multiple techniques can be used including frame-based approaches, frameless neuronavigation-guided approaches, or frameless­ approaches with intraoperative magnetic resonance imaging (MRI).8 Most stereotactic techniques use known atlas­ -based distances of the different nuclei (i.e., STN, GPi) in relation to the

midcommissural point (MCP), anterior commissure (AC), and posterior commissure (PC) ( Table 15.1). MRI images with specific volumetric T1-weighted seque nces and T2-weighted sequences delineate the GPi/STN very well.9 Direct techniques use MRI and/or computed tomography (CT) to visualize the nuclei in relation to known atlas coordinates and as such their strength lies in accounting for

patient’s anatomical variability usually in the order of millimeter differences. Indirect techniques are based on atlas coordinates and usually accompanied by intraoperative monitoring of patients’ neurophysiologic responses during stimulation and recording. Multiple stereotactic frames are available (e.g., Leksell’s,­ Cos- man-Roberts-Wells), and are user and institution dependent, providing the

surgeon millimeter accuracies. Entry points are chosen to avoid cortical, sulcal, subcortical, and periventricular vessels to reduce the risk of hemorrhage. Most common complications include intracranial hemorrhage (2.1%), infection within 6 months (4.5%), and hardware complications (as high as 8.4%).8

◦Technique: Place patient in a frame fixed to the table. Merge CT/MRI with calculated coordinates correlated with the frame. Make a bicoronal incision with uni-/bilateral burr holes 2 to 4 cm from midline at 1 to 2 cm anterior to the coronal suture. Open dura and coagulate pia. If electrophysiologic monitoring is performed, insert electrodes at defined offset and perform microelectrode recordings with stepwise movement with phys- iologic identification of targets based on nuclei specific frequency and pattern of activity. Once confirmed, placement of macroelectrode is performed and macrostimulation to determine benefits and side effect of stimulation. DBS electrode(s) is affixed to the skull and distal tips placed in the subgaleal space for future connection to an IPG. An IPG can be placed concurrently or at a later date, and involves placing patient supine, head tilted to the opposite side of the IPG. An infraclavicular subcutaneous pocket is created,

IPG placed, and connecting wires tunneled to the subgaleal pocket for connection to the distal electrode(s) tip ( Fig. 15.4).6,​8

Unilateral pallidotomy has similar efficacy as unilateral DBS, since pallidotomy currently can be only safely performed on one side.

•Pallidotomy: GPi discharge is abnormal PD and GPi pallidotomy helps address­ these abnormalities to relieve PD symptoms.

Good candidates for unilateral pallidotomy are patients with asymmetric symptoms, and those unable to comply with DBS ­follow-up and management.8 Main advantages include decreased infection risk given no hardware. Disadvantages include irreversible damage to GPi and surrounding structures, for example, corticospinal and optic tracts and if bilateral, a high risk of permanent speech and cognitive dysfunction.8 Pallidotomy uses the same localization tech- niques as those for DBS-GPi. Lesioning is most commonly performed using radiofrequency (RF) ablation, focused ultrasound (FUS) is currently under development for performing pallidotomy noninvasively.11 During pallidotomy, two key steps involve identification of the optic tract by eliciting

phosphenes in the contralateral visual field, and contralateral tetanization with macrostimulation near the internal capsule.12

15.1.2  Essential Tremor Diagnosis

Essential tremor (ET) is the most common movement disorder and is characterized as a benign, primarily postural, and/or kinetic tremor at a frequency of 4 to 12 Hz (higher than PD).13

In making the diagnosis of ET, careful characterization of the form of tremor needs to be undertaken: resting tremor, which occurs with a relaxed and stationary limb (e.g., PD); postural tremor, which

296

Fig. 15.4  DBS surgery. (a) Placement of Leksell’s

frame under local anesthesia. (b) OR table frame placement. (c) Sterile operative frame setup. (d) Full sample DBS

OR setup. (Reproduced from Sekhar L, Fessler R, Atlas of Neurosurgical Techniques: Brain, Volume 2, 2nd edition, ©2016, Thieme Publishers, New York.)9

occurs during voluntary held positions or substantial limb extension (e.g., ET); and intention tremor, which occurs as a limb approaches a target and is a coarse terminal tremor. ET is a clearly postural and/or intention tremor without resting tremor characteristics, with usual age of onset greater than 70 years, progressive in nature and mostly distal in location with greatest amplitude at the wrist and hand and with some form of asymmetry.14 It is more likely in women than men with prevalence of 0.4 to 6%,8,​15,​16,​17 and has autosomal dominant transmission.14 ET can be exacerbated by anxiety and improved by alcohol.16 Careful characterization of a patient with intention tremor can help distinguish ET from physiologic tremor and associated exacerbating factors (e.g., caffeine, smoking, drugs,

hyperthyroidism), other diseases (e.g., ­Parkinson’s tremor, dystonia, Wilson’s disease), and from secondary tremors (e.g., multiple sclerosis, stroke, trauma).7,​13

Diagnostic criteria for ET include the Movement Disorder Society and the Washington Heights Inwood Genetic Study of Essential Tremor criteria, which include the following criteria.

Inclusion criteria consist of bilateral postural tremor with or without intentional component of arms and forearms, and duration more than 5 years.

Exclusion criteria consist of other abnormal signs, known causes for increased physiologic tremor, current or recent use of tremor inducing drugs or drug withdrawal state, nervous system trauma within 3 months before onset of tremor, evidence of psychogenic signs, and evidence of sudden onset or stepwise deterioration.13

Pathophysiology

The pathophysiologic basis of ET is not as well understood as PD but consensus suggests mediation by a neuronal loop involving cerebellothalamocortical fibers with the ventral intermediate (VIM) nucleus of the thalamus as a key therapeutic target.13 The VIM contains two sets of tremor cells, whose input is primarily cerebellar and not striatal, and its output in part is hypothesized to target the pallidal tracts, serving as a major component of tremor circuitry connecting the cerebellum with cortical motor pathways.7,​15 These VIM cells fire in synchronous bursts with timing similar to peripheral tremor, with intraoperative stimulation noted to temporarily arrest tremor and as such have been posited as “tremorigenic pacemakers.”10,​16 ET is traditionally thought of as an autosomal dominant transmission with susceptibility loci at chromosomes 2, 3, and 6. Postmortem studies note significant cerebellar degenerative changes as well as brainstem Lewy bodies.

Treatment

Medical Therapy

Patients with severe ET are significantly impacted in their activities of daily living and are candidates for medical treatment.

First-line treatments for ET alone or in combination include β-blockers, (i.e., propranolol) and anticonvulsants (i.e., primidone) with class I evidence noting tremor reduction of up to 60% in 50% of patients.15

If failure of first-line agents occurs, patients can try second-line agents including benzodiazepines (e.g., clonazepam, alprazolam), gabapentin, calcium channel blockers (e.g., nimodipine), theophylline, and even botulinum toxin A, but additional treatments are rarely sufficient and at such point patients should undergo surgical

evaluation.6,​13,​15,​17

Surgical Therapy

Patients with medically refractory ET have two surgical options available with patients notable for distal extremity tremor benefitting most from surgery.6,​15

Current surgical options include VIM targeting via DBS or thalamotomy using either­ RF, SRS, or FUS.

•Deep brain stimulation: Unilateral or bilateral DBS of the VIM is a surgical option for upper extremity tremor control with success rates greater than 70%. A recent randomized controlled trial (RCT) of DBS VIM noted suppression of drug-resistant tremor with fewer ad-

297

verse effects than thalamotomy.6 DBS techniques are equivalent to those for PD noted above, but coordinates used to target the VIM are 11 mm lateral to the third ventricular wall, 5 to 6 mm anterior to the PC, and at the level of the AC/ PC line ( Table 15.2).

•Thalamotomy: There are currently three available means of performing VIM thalamotomy: the more common, invasive RF ablation approach, SRS, and a new, noninvasive FUS approach. Of note, irreversibility of thalamotomy is the major downside of such ablative procedures compared to DBS. Thalamotomy has been shown to reduce contralateral tremor in more than 85% of patients with notable transient (60%) versus mild permanent (23%) neurologic deficits

­including weakness, dysarthria, ataxia, and sensory deficits.10 In addition, bilateral thalamotomy is associated with greater than 50% cognitive and bulbar deficits, which makes bilateral DBS a preferred means of treating patients with severe bilateral tremor.7

FUS is performed by placing a patient in an MRI, followed by stereotactic targeting using known coordinates and MRI localization of the VIM target. The patient then undergoes sonication with acoustic energy to tissue ablative temperatures of 55 to 60°C, meanwhile undergoing real-time monitoring with MRI thermometry. FUS thalamotomy in a recent RCT showed almost 50% improvement in tremor scores in patients15 and is now a powerful option for treatment of ET in