Depth electrodes

Electrical Stimulation and Monitoring Devices of the CNS:

An Imaging Review

Sohil Patel MD1, Casey Halpern MD2, David Mossa RT1, Vincent Timpone MD3

1. NYU-Langone Medical Center, Dept of Radiology2. Stanford School of Medicine, Dept of Neurosurgery3. San Antonio Military Medical Center, Dept of Radiology

ASNR 2015 Electronic Educational Exhibit, #446

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.

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

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

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.

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

Subdural and depth electrodes

Intracranial EEG monitoring in an 18 year old with partial complex seizures.


Subdural grid electrodes (short solid arrows).


Depth electrodes (dashed arrows).


Wires connecting the intracranial leads to the external EEG recording device (long solid arrows).


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).


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

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.

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

Intraoperative radiographs show the normal positioning of bilateral foramen ovale electrodes (arrows). Both electrodes have 4 contact points.

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

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, parkinson’s 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

• Targets– Parkinson’s Disease

• Subthalamic nucleus• Globus pallidus internus

– Essential Tremor• Ventral intermediate nucleus of the thalamus

– Primary dystonia• Globus pallidus internus

– Obsessive compulsive disorder• Internal capsule anterior limb• Subthalamic nucleus


Bilateral DBS in a 78 year old male with Parkinson’s disease.


The components of the DBS system include the intracranial leads (solid short arrows) which contain 4 electrode contacts at their distal tips (arrowheads).


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.


Coronal T1WI shows bilateral DBS electrodes terminating in the subthalamic nuclei (arrows) in this patient with Parkinson’s disease.


Axial and coronal T1WI show bilateral DBS electrodes (arrows) within the globus pallidus internus in this 64 year old female with dystonia.

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.

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.

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.

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).

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).

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.

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.


The neurostimulator cassette (solid arrows) has been implanted within a parietotemporal craniectomy bed. Neurostimulator cassette within a skull model (dashed arrow) for comparison.


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.

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.

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.

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).

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.

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.

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.

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.

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.

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 4th 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.

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.

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 4th 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

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 4th ventricular lateral recess, abutting the dorsal lateral surface of the cochlear nucleus.

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.

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.

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.

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.

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.

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).

Spinal Cord Stimulator

CT images from same patient demonstrate the desired posterior epidural placement of the electrodes (dashed arrows).

Complications of implanting neurologic stimulators/monitoring devices

• Infection• Hemorrhage• Infarction• Vascular injury• Device malpositioning• Lead fracture• Lead disconnection

Complications - infection

21 year old female with complex partial seizures. Intracranial EEG recording withsubdural grid (solid arrows) and depth electrodes (dashed arrows) was undertaken.

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.

References1.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.

References11.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;31:722–3020.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.

References21. 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):1228-3722. Finley CC, Holden TA, Holden LK, et al. Role of electrode placement as a contributor to variability in cochlear implant outcomes. Otol Neurotol 2008;29:920–2823. Colby CC, Todd NW, Harnsberger HR, Hudgins PA. Standardization of CT Depiction of Cochlear Implant Insertion Depth. AJNR. 2015 Feb;36(2):368-7124. 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; 19:264–268. 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

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