Electrical Stimulation and Monitoring Devices of the CNS: An
Imaging Review Sohil Patel MD 1, Casey Halpern MD 2, David Mossa RT
1, Vincent Timpone MD 3 1. NYU-Langone Medical Center, Dept of
Radiology 2. Stanford School of Medicine, Dept of Neurosurgery 3.
San Antonio Military Medical Center, Dept of Radiology ASNR 2015
Electronic Educational Exhibit, #446
Slide 2
Disclosures No financial disclosures. The opinions and views
expressed in this presentation are solely those of the authors and
do not represent an endorsement by or the views of the Department
of Defense, or the United States Government.
Slide 3
Aims To familiarize the radiologist with various implanted
electrical neurological monitoring and stimulator devices,
including their: Clinical indications Normal components and
function Expected imaging appearance Potential complications MRI
compatibility
Slide 4
Content Subdural and Depth electrodes Foramen ovale electrodes
Deep brain stimulation Motor cortex stimulator Responsive
neurostimulation Middle ear implant Auditory brainstem implant
Cochlear implant Vagal nerve stimulator Spinal stimulator
Slide 5
Subdural and depth electrodes Intracranial electrodes placed in
epilepsy patients to record brain electrical activity. Requires
craniotomy or burr hole access. Subdural electrodes are arranged as
a strip or grid array along the surface of the brain. Depth
electrodes are linear electrodes placed directly into the brain
parenchyma.
Slide 6
Subdural and depth electrodes Indications: Seizure
localization: Indicated in patients with medically refractory
seizures, whose non-invasive tests (ie. scalp EEG with video
monitoring, MRI) are inconclusive or discordant with respect to
seizure localization/laterality. Minimization of surgical resection
Intracranial EEG allows higher spatial and temporal resolution than
scalp EEG. This may allow minimization of the subsequent surgical
resection. Detection of eloquent cortex Electrodes can be
stimulated to localize nearby eloquent cortex. MRI compatibility:
Safe and conditional devices exist for scanning at 1.5T
Slide 7
Subdural and depth electrodes Intracranial EEG monitoring in an
18 year old with partial complex seizures.
Slide 8
Subdural and depth electrodes Subdural grid electrodes (short
solid arrows).
Slide 9
Subdural and depth electrodes Depth electrodes (dashed
arrows).
Slide 10
Subdural and depth electrodes Wires connecting the intracranial
leads to the external EEG recording device (long solid
arrows).
Slide 11
Subdural and depth electrodes Axial T2WI (right) and T1WI
(left) show subdural electrodes (solid arrows) and depth electrodes
(dashed arrows). Changes from left temporal-occipital craniectomy
are noted. Axial CT, maximum intensity projection, shows bilateral
depth electrodes (dashed arrows).
Slide 12
Subdural and depth electrodes Image from intraoperative
neuronavigation shows the planned trajectory of a depth electrode
(solid arrow) into a region of polymicrogyria (dashed arrow).
Intraoperative image from placement of a depth electrode
Slide 13
Foramen ovale electrodes Intracranial linear electrodes placed
to record medial temporal lobe electrical activity. The electrodes
are inserted via a trans-facial percutaneous approach with
fluoroscopic guidance. The electrodes are placed into the ambient
cisterns, adjacent to the medial temporal lobes.
Slide 14
Foramen ovale electrodes Indicated in patients with suspected
medial temporal lobe epilepsy, but with unconfirmed
localization/laterality based on non-invasive testing. Foramen
ovale electrodes provide higher spatial and temporal resolution
than scalp EEG. Compared to subdural/depth electrodes, foramen
ovale electrodes: Do not require craniotomy/burr hole. Are not
placed into brain parenchyma. Evaluate only medial temporal lobes.
MRI compatibility: Safe and conditional devices exist for scanning
at 1.5T
Slide 15
Intraoperative radiographs show the normal positioning of
bilateral foramen ovale electrodes (arrows). Both electrodes have 4
contact points.
Slide 16
Axial CT scan image shows foramen ovale electrodes in the
ambient cisterns, adjacent to the medial temporal lobes (solid
arrows). Coronal CT scan images show the electrodes traversing
bilateral foramen ovale (dashed arrows). Foramen ovale
electrodes
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Deep brain stimulation (DBS) Intracranial electrodes that
produce electrical stimulation of functional targets in the brain
parenchyma. DBS electrodes are placed via burr holes or craniotomy.
Guided to targets using image-guided neuronavigation and
neurophysiologic recording. FDA approval for treatment of essential
tremor, parkinsons disease, primary dystonia, obsessive compulsive
disorder. Off-label use in the treatment of refractory depression,
chronic pain, epilepsy, and Tourette syndrome. MRI compatibility:
Conditional devices exist for scanning at 1.5T
Deep brain stimulation Bilateral DBS in a 78 year old male with
Parkinsons disease.
Slide 20
Deep brain stimulation The components of the DBS system include
the intracranial leads (solid short arrows) which contain 4
electrode contacts at their distal tips (arrowheads).
Slide 21
Deep brain stimulation The intracranial electrodes are
connected, via extension wires (long solid arrows), to the pulse
generators (dashed arrows) which are implanted subcutaneously in
the chest wall.
Slide 22
Deep brain stimulation Coronal T1WI shows bilateral DBS
electrodes terminating in the subthalamic nuclei (arrows) in this
patient with Parkinsons disease.
Slide 23
Deep brain stimulation Axial and coronal T1WI show bilateral
DBS electrodes (arrows) within the globus pallidus internus in this
64 year old female with dystonia.
Slide 24
Deep brain stimulation Off-label use for the treatment of
epilepsy. Targets include hippocampus/amygdala and the thalamus. In
medial temporal lobe epilepsy, DBS indicated if patients are:
Refractory to medical treatment Unsuitable for surgical therapy due
to: Bilateral disease Surgical risk of major verbal memory loss
(assessed with intraarterial amobarbital testing). Temporal lobe
stimulators in a patient with intractable epilepsy. Electrodes
(arrows) lie within the medial temporal lobes.
Slide 25
Motor cortex stimulator Used in patients with refractory pain
syndromes. Strip electrodes are placed in the epidural space
overlying the motor cortex via craniotomy approach. The motor
cortical representation of the painful site is targeted (ie.
contralateral to side of pain). The electrodes are guided to the
appropriate location using image-guided neuronavigation and
intraoperative neurophysiologic testing. After appropriate
positioning, the lead is sutured to the dura, and connected via
extension wiring to a pulse generator that is implanted in the
chest wall subcutaneous tissues.
Slide 26
Motor cortex stimulator Variable success in the treatment of a
variety of pain syndromes, including Trigeminal neuralgia
Post-stroke pain Phantom limb pain Herpetic neuralgia Multiple
sclerosis. Usage is off-label. MRI compatibility: Unknown.
Slide 27
Motor cortex stimulator Lateral scout radiograph shows a
4-contact motor cortex electrode (solid arrow). The intracranial
lead is connected to a pulse generator (not shown) via extension
wiring (arrowhead) that is tunneled through the neck subcutaneous
tissue. Axial CT images from the same patient show the intracranial
lead (solid arrow) within the epidural space overlying the left
motor strip (dashed arrow).
Slide 28
Responsive Neurostimulation FDA approved for the treatment of
medication refractory partial onset seizures in adults. The
responsive neurostimulator device records and processes EEG data
from targeted brain regions. It delivers electrical stimulation to
these targets upon detection of seizure activity. The electrical
stimulation disrupts the seizure activity. The neurostimulator
cassette (containing the pulse generator) is implanted in the
calvarium. The neurostimulator is connected to either cortical
strip leads (which are placed on the brain surface) or depth leads
(which are placed in the brain parenchyma).
Slide 29
Responsive Neurostimulation Shown to lower seizures rates by
50% on average. The therapeutic efficacy might increase over time
via neuromodulatory effects. Compared to surgical therapy:
Different sites (up to two) can be targeted. Eloquent regions can
be targeted without disruption Reversible (the device can be
removed). Compared with DBS: Responsive neurostimulation does not
provide continuous stimulation. Rather, it is triggered by the
detection of seizure activity. MRI compatibility: Not MRI
compatible.
Slide 30
Responsive Neurostimulation Scout radiographs and axial CT
images show an implanted Responsive Neurostimulator device in a 24
year old female with medication resistant partial complex
seizures.
Slide 31
Responsive Neurostimulation The neurostimulator cassette (solid
arrows) has been implanted within a parietotemporal craniectomy
bed. Neurostimulator cassette within a skull model (dashed arrow)
for comparison.
Slide 32
Responsive Neurostimulation Four electrodes were implanted
(arrows). Intraoperative electrocorticography was performed from
each electrode. The neurostimulator was connected to two of the
electrodes which recorded the greatest seizure activity. The
remaining two electrodes were left in place but were not connected
to the neurostimulator.
Slide 33
Middle Ear Implant Electronic device that converts sound energy
into mechanical vibrations that directly stimulate middle ear
structures. Externally worn audioprocessor receives and transmits
signal to vibrating ossicular prosthesis embedded subcutaneously
overlying the temporal bone. Vibrating ossicular prosthesis
transmits signal to middle ear transducer which is attached to
incus or round window and causes these structures to vibrate and
amplify acoustic input to cochlea.
Slide 34
Middle Ear Implant Indications: Moderate to severe
sensorineural hearing loss in patients with suboptimal response to
traditional hearing aid devices, or medical contraindication to
such devices (ie otitis externa). Compared to conventional external
hearing aid devices: Similar hearing thresholds Improved sound
quality, less feedback Improved comfort and patient satisfaction
Potential complications: Bleeding, infections, facial nerve injury.
MR compatibility: No current MR compatible devices available.
Slide 35
Middle Ear Implant 36 yo female with mixed hearing loss.
Vibrating ossicular prosthesis implanted under the skin (solid
arrow) receives input from an externally worn audioprocessor (not
shown) and transfers signal to a vibrating middle ear transducer
(dashed arrow).
Slide 36
Middle Ear Implant CT images from same patient demonstrating
subcutaneous vibrating ossicular prosthesis (solid arrow),
electrode (arrowhead), and transducer (dashed arrow) implanted
adjacent to the round window. In patients with normal ossicles,
transducer may be attached to the incus.
Slide 37
Cochlear Implant Implanted electronic hearing device converting
sound energey into electronic impulses that directly stimulate the
cochlea. Sound signal detected by an external microphone and
audioprocessor. Audioprocessor is magnetically attached to an
implanted receiver-stimulator seated within the temporal bone.
Receiver-stimulator converts signal transmitted from audioprocessor
into electrical impulses that stimulate the cochlea via a soft
flexible electrode array.
Slide 38
Cochlear Implant Indications: Severe to profound sensorineural
hearing loss. Majority of patients demonstrate significant
improvement in measurements of speech recognition though results
vary based on age at implantation and duration of hearing loss.
Several studies suggest improved functional outcome with greater
insertion depth and when electrode located in the scala tympani.
Cochlea coordinate system developed by consensus panel in 2010 and
enables viewers to communicate implant array location with less
ambiguity. Potential complications: Facial nerve injury, CSF leak,
loss of residual hearing. MR compatibility: MR conditional devices
available.
Slide 39
Cochlear Implant 40 yo female with bilateral sensorineural
hearing loss treated with bilateral cochlear implants.
Receiver-stimulators (solid arrows) are embedded to the temporal
bone. Flexible array electrodes (dashed arrows) are seen coiled
within the cochlea, approximately 360 degrees on the right, 180
degrees on the left.
Slide 40
Cochlear Implant CT images from same patient demonstrating
electrodes coiled within the cochlea, with electrode tips
visualized (solid arrow). Using standardized cochlear coordinate
system, electrode tips are positioned at approximately segment 5 on
the right, segment 3 on the left.
Slide 41
Auditory Brainstem Implant Electronic device which stimulates
cochlear nucleus directly and provides sound sensation to an
otherwise deaf patient. Paddle array electrode placed in lateral
recess of 4 th ventricle overlying dorsal-lateral surface of
cochlear nucleus. Electrode connects to receiver-transmitter seated
within the temporal bone. Sound picked up by microphone at pinna,
signal then sent to pocket sized speech processor worn on the
patient. Speech processor changes sound signal to an electronic
impulse sent to the receiver through a transmitter coil.
Slide 42
Auditory Brainstem Implant Indications: Patients without
functioning cochlea or cochlear nerve, but with intact auditory
brainstem pathway: Bilateral vestibular schwannomas in
Neurofibromatosis II Skull-base trauma with cochlea damage
Congenitally absent cochlear nerve In clinical studies, >80% of
patients able to detect familiar sounds (ie doorbell, honking horn)
and demonstrate improved understanding of conversation with aid of
lip-reading. Potential complications: Non-auditory stimulation of
other cranial nerves if electrode placed too far ventrally MR
Compatibility: MR conditional devices available.
Slide 43
Auditory Brainstem Implant A. Demonstrates the
receiver-stimulator component that has a grounding electrode
embedded underneath temporalis muscle, and multichannel electrode
paddle inserted into the 4 th ventricle lateral recess. B. External
components include microphone which sends sound to
processor-digitizer which in turn sends electrical impulses to the
receiver via the transmitter coil. Lekovic et al: Auditory
Brainstem Implantation
Slide 44
Auditory Brainstem Implant Auditory brainstem implant in 25 yo
male with Neurofibromatosis type 2 and bilateral sensorineural
hearing loss. Receiver-stimulator embedded within the temporal bone
(solid arrow) connected to electrode paddle (dashed arrow) located
in the 4 th ventricular lateral recess, abutting the dorsal lateral
surface of the cochlear nucleus.
Slide 45
Vagal Nerve Stimulator Stimulation of vagal cervical trunk to
treat wide variety of disorders, most commonly medically refractory
epilepsy and depression. Small electrode implanted around the left
vagus nerve cervical trunk, approximately 8cm above the clavicle
and connected to a programmable generator placed subcutaneously in
the upper thorax. Mechanism of action not fully understood, however
afferent vagal fiber activation appears to disrupt seizure-related
circuitry. Vagal nerve stimulation may also alter neurotransmitter
and metabolite concentrations leading to antidepressant
effects.
Slide 46
Vagal Nerve Stimulator Right sided vagus nerve stimulation
thought to result in increased cardiac side effects. Only left
sided vagus nerve stimulators currently FDA approved. In clinical
studies: Greater than 50% reduction in seizure frequency, as well
as reduced seizure duration and post-ictal recovery times. Greater
than 50% reduction in depression scores after 12 months of therapy.
Potential complications: vocal cord paresis, dysphagia. MR
compatibility: MR conditional devices available.
Slide 47
Vagal Nerve Stimulator 53 yo with epilepsy treated with vagal
nerve stimulation. Subcutaneous pulse generator (solid arrow) is
seen in the upper left thorax and is connected to a coiled
electrode (dashed arrow) attached to the left cervical vagus
trunk.
Slide 48
Spinal Cord Stimulator Electronic device which stimulates
posterior columns of spinal cord in treatment of chronic pain. With
stimulation patient will feel mild paresthesias in their area of
pain, which inhibits transmission of other nociceptive inputs,
reducing overall level of pain. 3 components: Generator: implanted
under the skin and sends electrical impulses to electrodes.
Electrodes: inserted into the posterior epidural space and threaded
to the desired level under fluoroscopic guidance. Wireless
programmable controller: regulates stimulation.
Slide 49
Spinal Cord Stimulator Indications: Treatment resistant chronic
back/extremity pain. Failed back surgery syndrome In selected
patients, spinal cord stimulation more effective and less expensive
than reoperation for treatment of persistent post-operative
radicular pain. Potential complications: CSF leak. MR
compatibility: MR conditional devices available.
Slide 50
Spinal Cord Stimulator 64 yo female with chronic cervicalga.
Subcutaneous pulse generator (solid arrow) is seen in the left
lower flank, connected to 2 leads each with 4 electrode contact
points at their distal tip in the cervical spine (dashed
arrow).
Slide 51
Spinal Cord Stimulator CT images from same patient demonstrate
the desired posterior epidural placement of the electrodes (dashed
arrows).
Slide 52
Complications of implanting neurologic stimulators/monitoring
devices Infection Hemorrhage Infarction Vascular injury Device
malpositioning Lead fracture Lead disconnection
Slide 53
Complications - infection 21 year old female with complex
partial seizures. Intracranial EEG recording with subdural grid
(solid arrows) and depth electrodes (dashed arrows) was
undertaken.
Slide 54
Complications - infection The patient returned to emergency
department 2 months after the electrodes were removed, complaining
of swelling and discharge near the craniotomy site. When compared
to the axial CT image with intracranial electrodes in place (left
image), the axial CT image 2 months later (right image) shows new
erosions (arrowheads) in the bone flap. At surgical pathology, this
proved to represent osteomyelitis of the bone flap.
Slide 55
References 1.Ben-Menachem E, Krauss GL: Epilepsy: responsive
neurostimulation-modulating the epileptic brain. Nature reviews
Neurology 2014, 10(5):247-248. 2.Blount JP, Cormier J, Kim H,
Kankirawatana P, Riley KO, Knowlton RC: Advances in intracranial
monitoring. Neurosurgical focus 2008, 25(3):E18. 3.Boex C, Seeck M,
Vulliemoz S, Rossetti AO, Staedler C, Spinelli L, Pegna AJ, Pralong
E, Villemure JG, Foletti G et al: Chronic deep brain stimulation in
mesial temporal lobe epilepsy. Seizure 2011, 20(6):485-490.
4.Carmichael DW, Thornton JS, Rodionov R, Thornton R, McEvoy A,
Allen PJ, Lemieux L: Safety of localizing epilepsy monitoring
intracranial electroencephalograph electrodes using MRI:
radiofrequency-induced heating. Journal of magnetic resonance
imaging : JMRI 2008, 28(5):1233-1244. 5.Chen XL, Xiong YY, Xu GL,
Liu XF: Deep brain stimulation. Interventional neurology 2013,
1(3-4):200-212. 6.Cox JH, Seri S, Cavanna AE: Clinical utility of
implantable neurostimulation devices as adjunctive treatment of
uncontrolled seizures. Neuropsychiatric disease and treatment 2014,
10:2191-2200. 7.Davis LM, Spencer DD, Spencer SS, Bronen RA: MR
imaging of implanted depth and subdural electrodes: is it safe?
Epilepsy research 1999, 35(2):95-98. 8.Fisher RS, Velasco AL:
Electrical brain stimulation for epilepsy. Nature reviews Neurology
2014, 10(5):261-270. 9.Heck CN, King-Stephens D, Massey AD, Nair
DR, Jobst BC, Barkley GL, Salanova V, Cole AJ, Smith MC, Gwinn RP
et al: Two-year seizure reduction in adults with medically
intractable partial onset epilepsy treated with responsive
neurostimulation: final results of the RNS System Pivotal trial.
Epilepsia 2014, 55(3):432-441. 10.Henderson JM, Lad SP: Motor
cortex stimulation and neuropathic facial pain. Neurosurgical focus
2006, 21(6):E6.
Slide 56
References 11.Jenkins HA, Uhler K: Otologics Active Middle Ear
Implants. Otolaryngologic clinics of North America 2014, 47(6):967-
978. 12.Lefaucheur JP, Drouot X, Cunin P, Bruckert R, Lepetit H,
Creange A, Wolkenstein P, Maison P, Keravel Y, Nguyen JP: Motor
cortex stimulation for the treatment of refractory peripheral
neuropathic pain. Brain : a journal of neurology 2009, 132(Pt
6):1463-1471. 13.Merkus P, Di Lella F, Di Trapani G, Pasanisi E,
Beltrame MA, Zanetti D, Negri M, Sanna M: Indications and
contraindications of auditory brainstem implants: systematic review
and illustrative cases. European archives of oto- rhino-laryngology
: official journal of the European Federation of
Oto-Rhino-Laryngological Societies 2014, 271(1):3-13. 14.Morrell
MJ, Group RNSSiES: Responsive cortical stimulation for the
treatment of medically intractable partial epilepsy. Neurology
2011, 77(13):1295-1304. 15.Rushton DN: Electrical stimulation in
the treatment of pain. Disability and rehabilitation 2002,
24(8):407-415. 16.Sheth SA, Aronson JP, Shafi MM, Phillips HW,
Velez-Ruiz N, Walcott BP, Kwon CS, Mian MK, Dykstra AR, Cole A et
al: Utility of foramen ovale electrodes in mesial temporal lobe
epilepsy. Epilepsia 2014, 55(5):713-724. 17.Yang AI, Wang X, Doyle
WK, Halgren E, Carlson C, Belcher TL, Cash SS, Devinsky O, Thesen
T: Localization of dense intracranial electrode arrays using
magnetic resonance imaging. NeuroImage 2012, 63(1):157-165. 18.Yuan
J, Chen Y, Hirsch E: Intracranial electrodes in the presurgical
evaluation of epilepsy. Neurological sciences : official journal of
the Italian Neurological Society and of the Italian Society of
Clinical Neurophysiology 2012, 33(4):723- 729. 19. Verbist BM,
Skinner MW, Cohen LT, et al. Consensus panel on a cochlear
coordinate system applicable in histologic, physiologic, and
radiologic studies of the human cochlea. Otol Neurotol
2010;31:72230 20.Beltrame AM, Martini A, Prosser S, Giarbini N,
Streitberger C. Coupling the Vibrant Soundbridge to cochlea round
window: auditory results in patients with mixed hearing loss. Otol
Neurotol. 2009 Feb;30(2):194-201.
Slide 57
References 21. Kahue CN, Carlson ML, Daugherty JA, Haynes DS,
Glasscock ME 3rd. Middle ear implants for rehabilitation of
sensorineural hearing loss: a systematic review of FDA approved
devices. Otol Neurotol. 2014 Aug;35(7):1228-37 22. Finley CC,
Holden TA, Holden LK, et al. Role of electrode placement as a
contributor to variability in cochlear implant outcomes. Otol
Neurotol 2008;29:92028 23. Colby CC, Todd NW, Harnsberger HR,
Hudgins PA. Standardization of CT Depiction of Cochlear Implant
Insertion Depth. AJNR. 2015 Feb;36(2):368-71 24. Manchikanti, L,
Boswell MV, et al. Comprehensive review of therapeutic
interventions in managing chronic spinal pain. Pain Physician. 2009
Jul-Aug;12(4):E123-98. 25. Kumar K, Taylor RS, Jacques L et al.
Spinal cord stimulation versus conventional medical management for
neuropathic pain: a multicentre randomised controlled trial in
patients with failed back surgery syndrome. Pain 2007;132:179-188.
26. Lekovic G, Gonzalez F, Syms M, Daspit C, Porter R. Auditory
Braintstem Implantation. Barrow quarterly vol (20) no 4 2004. 27.
Ghaemi K, Elsharkawy AE, Schulz R et al. Vagus nerve stimulation:
outcome and predictors of seizure freedom in long-term follow-up.
Seizure 2010; 19:264268. 28. Beekwilder JP, Beems T. Overview of
the clinical applications of vagus nerve stimulation. J Clin
Neurophysiol. 2010 Apr;27(2):130-8. 29. www.fda.gov