5.3.6.1\ Discussion

5.3.7\ Neural Interface System

(BrainGate)

5.3.7.1\ Discussion

The BrainGate is a neural interface system that is used to decode neural signals in order to control a computer program or artificial arm in paraplegic­ patients, such as those with amyotrophic lateral

a

c

sclerosis. The system essentially converts thought into action. The device consists of a minute subcortical silicon electrode array sensor that is implanted along the motor strip region of the arm via microcraniotomy and wires run from the electrode to a post affixed to the surface of the skull (Fig. 5.42). The main complications include hemorrhage and infection.

b

Fig. 5.42  BrainGate. The patient has a history of amyotrophic lateral sclerosis with quadriplegia and locked-in syndrome. Lateral (a) scout image and axial (b) and

coronal (c) CT images show the tiny electrode array (arrow) implanted in the arm motor strip region connected via wires to the post attached to the skull

5.3.8\ Microcatheter Subthalamic

Infusion of Glutamate

Decarboxylase

5.3.8.1\ Discussion

Gene transfer of glutamic acid decarboxylase (GAD) is a promising treatment for medically intractable Parkinsonism. The vector for GAD is injected into the subthalamic nuclei via microcatheters­ . GAD modulates the production of GABA in the subthalamic nucleus and improves basal ganglia function. A small quantity, approximately 35 μl, of the vector solution is infused and is usually not appreciable on imaging. However, the fine microelectrode tracts may be visible (Fig. 5.43).

Fig. 5.43  Subthalamic infusion of glutamate decarboxylase. Coronal post-contrast T1-weighted MRI shows bilateral thin microcatheter tracts (arrows) leading toward the subthalamic nuclei. The microcatheters were introduced via bifrontal burr holes

5.3.9\ Seizure Monitoring Electrodes

and NeuroPace

5.3.9.1\ Discussion

Subdural electrode grids and arrays provide electrographic monitoring to localize seizure foci for possible resection. These can be implanted as arrays of individual strips (Figs. 5.44 and 5.45). The electrode grids can cover a large area and require craniotomy for implantation, while individual strips can be inserted through burr holes. The duration of monitoring can last days to weeks. Once the seizure focus is identified, the electrodes can be removed at the time of therapeutic epileptogenic tissue resection. Alternatively, the electrodes can be removed noninvasively if bioresorbable components are utilized.

Depth electrodes are also used to monitor epilepsy in patients with non-lateralizing scalp EEG and/or discordant imaging studies. However, in contrast to subdural electrode placement, depth electrodes are inserted into the brain parenchyma through burr holes (Fig. 5.46). Consequently, the recorded seizure discharges are usually better developed in the depth electrodes. Yet another approach for seizure monitoring is insertion of the electrodes through the foramen ovale (Fig. 5.47). These can be particularly useful for lateralization of temporal lobe activity.

NeuroPace is a device used for both the detection and treatment of medically refractory partial epilepsy. The device components include a neurostimulator, depth leads, and cortical strip leads (Fig. 5.48). The neurostimulator is a

programmable,battery-powered,microprocessor- controlled device that delivers a short train of electrical pulses to the brain through implanted leads. A wand and telemetry interface is used for communication with the implanted neurostimulator, allowing the recorded electrocorticogram to be viewed in real time on a computer using specialized software. The neurostimulator can detect abnormal electrical activity in the brain and respond by delivering electrical stimulation

to normalize brain activity before the patient experiences seizure symptoms.

Complications associated with electrode grid implantation occur in 3–8% of cases and mainly include subdural hematomas (Fig. 5.49) and infection (Fig. 5.50). Epidural hematomas and cerebral edema are less common. Imaging plays a role in identifying such complications, although the associated streak artifact from the grids on CT limits a detailed assessment.

Fig. 5.44  Electrode strips. Axial CT image (a) shows the electrode wires coursing through a temporal burr hole. The electrodes are positioned along the surface of the

brain in the middle and posterior fossa. CT volume intensity­ projection (VIP) image (b) shows the course of bilateral electrode strips

Fig. 5.45  Electrode grids. CT scout image (a) shows the 64-channel electrode grid in position. Axial CT image (b) shows the metallic subdural electrode grid array overlying

the left cerebral hemisphere. Photograph of subdural grid and strip electrodes (c)

Fig. 5.50  Electrode-associated infection. The patient presented with fever and drainage from site of the subdural electrode insertion. Axial CT image (a) shows a gas-­ containing subdural collection overlying the deep brain electrodes. The subdural electrodes were then removed.

The axial post-contrast T1-weighted MRI (b) shows a ring-­enhancing collection in the right frontal lobe (arrow), as well as regional leptomeningeal and pachymeningeal enhancement