Deep Brain Stimulation of the Subthalamic Nucleus for Parkinson Disease

Equipment

Stereotactic planning software, stereotactic frame, microelectrode recording (MER) hardware, fluoroscopy

Anesthetic Issues

Intravenous antibiotics 30 min prior to skin incision and repeat periodically during the procedure
Propofol can be started once the head frame is fixed in position. Give local anesthetic prior to incision. Stop sedation as soon as burr hole is made, prior to MER.
If patient is in need of sedation intraoperatively, consider the use of dexme-detomidine during MER.
Maintain systolic blood pressure (SBP) < 140 throughout case, to reduce risk of hemorrhage.

Head-Frame and Image Acquisition

Head-frame can be placed under local anesthesia. Align frame to the orbito-cranial line to approximate its alignment to the anterior commissure (AC)–posterior commissure (PC) line.
Frameless technology is a valid alternative for DBS surgery.
Acquire computed tomography (CT)/magnetic resonance imaging (MRI) stereotactic scans with fiducials (frame or frameless) in place.
Axial T1 volumetric MRI with contrast, T2 thin cuts through basal ganglia/subthalamic nucleus (STN).

Positioning and Preparation

Secure frame while patient supine and check for comfort.
Careful prepping and draping. Optimize room sterility for an implant procedure with ventriculoperitoneal shunt infection precautions.

Operative Planning

Direct targeting: target posterior-ventral STN at or behind anterior border of red nucleus on T2s.
Indirect targeting: based on AC–PC coordinates; commonly 11 to 13 mm lateral to AC–PC line, 3 to 4 mm posterior to midcommissural point, and 3 to 5 mm below AC–PC line.
Fuse stereotactic CT with MRI to obtain frame based coordinates (can use CT or MRI directly).
Set entry at or just in front of coronal suture. Penetration can be planned at 5 to 15 degrees off the midline in the coronal plane. Assess trajectory for proximity to blood vessels and modify entry site (and angles of approach) as appropriate to prevent vessel injury and hemorrhages. Can use “Probes eye” view for trajectory planning.

Surgery

With the frame and arc in the appropriate coordinates, mark the burr hole position.
Skin incision centered on burr hole. Make burr hole centered on stereotactically identified entry point, using 14 mm bit. Ask anesthesia to stop the sedation.
Before opening dura, place Navigus burr hole device (Image Guided Neurologics, Inc., Melbourne, FL) (for securing lead in place), supplied with DBS electrode. Once secured, ensure lead grasping clip fits well and locks. Alternatively, a titanium bioplate may be used (lower profile). Cruciate dural incision, coagulate edges back with bipolar electrocautery. Insert cannula to above target, with exact distance depending on your microdrive system.
Advance microelectrode with microdrive, record top and bottom of thalamus and STN and substantia nigra pars reticulata. Once in STN, check for somatosensory driving of joints.
Stimulation with microelectrode although not necessary, if available, can be used to assess proximity to internal capsule. Look for tongue, face, finger, and foot twitches at 0 to 90 microamps.
A track with ~5 mm through the STN, good somatosensory driving, and no capsular activation with microstimulation is usually adequate for DBS electrode implantation. A lateral track to determine border with internal capsule may be helpful to avoid capsular side effects.
Prior to placement of DBS lead, check baseline tremor, rigidity, and bradykinesia. Two leads available currently: 3387 and 3389; 3389 used more commonly in STN.

Macrostimulation

Once DBS lead is in place, test with macrostimulation. Bipolar stimulation using contacts 0, 1, and 2 as cathodes and 3 as anode. Typical stimulation settings are 60 to 90 microseconds PW and 130 to 185 Hz rate. Start at 1 V and increment step-wise. At each increment, check for effects on tremor, rigidity, and bradykinesia. Establish the threshold for side effects for each contact. Muscle contractions at low thresholds indicate that the electrode is either too lateral or too anterior. Persistent paresthesias indicate a posteriorly placed electrode. Dysconjugate eye deviation suggests activation of the third cranial nerve fibers, medial to STN. Conjugate eye deviation suggests lead is too anterior. Mouth involvement with 4 V or less usually requires repositioning of the lead.
When satisfied with the benefit-to-side-effect ratio, pull back guide cannula and place Navigus clip to secure lead under fluoroscopy. Pull guide wire out and disassemble motor drive.
Place temporary connector and boot over the distal tip of DBS electrode. Bury in pocket leaving a loop around the Navigus. Irrigate thoroughly, closure in two layers.

Stage II (Implantation of Generator)

Position with head turned and shoulder roll under neck and shoulder for easier/safer tunneling
Find connector, plan incision partially over connector
Make chest wall incision three fingerbreadths lateral to manubrium and one fingerbreadth inferior to clavicle, make subcutaneous (or subfascial in thin patients) pocket. Tunnel down from parietal incision and pass the extension wire.
Connect the distal end of the wire to the pulse generator and the proximal end to the lead.
Place pulse generator in chest pocket, ensuring the extension wire is underneath it, and secure with silk sutures.

Intensive care unit or step-down care for 24 hours. Keep SBP under control, intravenous antibiotics for 24 hours.
Ensure patient gets Parkinson medications as soon as possible
Anteroposterior lateral skull x-ray and CT. Early mobilization, heparin subcutaneously, or enoxaparin on postoperative day 1 if CT is okay.