Avoidance, Recognition, and Treatment of Complications in Cranial Neuromodulation for Pain

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Chapter 4 Avoidance, Recognition, and Treatment of Complications in Cranial Neuromodulation for Pain

Parag G. Patil

Chapter Overview

Chapter Synopsis: Deep brain stimulation (DBS) was initially used as a therapy for medically intractable chronic pain; the technique is not approved by the U.S. Food and Drug Administration (FDA) for this application and is rarely used today. Nevertheless, some centers have found success with DBS and with motor cortex stimulation (MCS) for pain. Similar to any invasive brain surgery, complications may arise; surgical, hardware-related, and stimulation-related risks are most notable.

Important Points:

image Although not currently labeled for use in the United States for the treatment of pain, DBS and MCS are potentially effective therapies for medically intractable pain in carefully selected patients.
image Complications of these therapies may arise during surgery from hardware complications, tissue injury, and from the undesired effects of stimulation.
image Because few patients are treated with cranial neuromodulation, the precise rates of complications are largely unknown, although the characteristics of these complications are well defined.
image Major complications of intracranial neuromodulation are hemorrhage and infection.
image Attention to surgical technique can minimize these complications.

Introduction

Cranial forms of neuromodulation for pain include deep brain stimulation (DBS), motor cortex stimulation (MCS), and non-invasive forms of electrical stimulation such as transcranial magnetic stimulation and transcranial direct-current stimulation.1 DBS and MCS involve the surgical implantation of electrodes within the brain or in the epidural space, respectively. The DBS and MCS electrodes are then connected subcutaneously to an implantable pulse generator (IPG), most often located in the chest. As with other forms of surgical neuromodulation, careful patient selection is critical to the success of DBS and MCS for pain, and a trial of externally driven stimulation is typically performed before placement of the IPG.

Neither DBS for pain nor MCS for pain are performed with great frequency anywhere in the world. As a result, published accounts of these procedures are primarily in the form of case reports and case series. In addition, clinically significant complications in these procedures are rare, in the range of 1% to 10%. For this reason, precise estimates of rates of complications are difficult to determine for either DBS or MCS for pain, although the nature of these complications has been described well. In this chapter, the clinically significant complications of DBS and MCS are described, with emphasis on some strategies used in neurosurgical practice to avoid these adverse outcomes.

Deep Brain Stimulation for Pain

Deep brain stimulation for medically refractory pain was the first application of chronic intracranial DBS. In 1973 Hosobuchi et al2 implanted a stimulating electrode into the ventroposteromedial (VPM) thalamus to treat facial pain. Chronic stimulation was attempted after the observation by Hosobuchi and others that acute stimulation before lesion placement resulted in pain improvement. Today, DBS for medically intractable pain typically targets two regions, the sensory ventroposterolateral (VPL)/VPM thalamus and the periaqueductal/periventricular (PAG/PVG) grey matter. Common indications for DBS for pain include chronic poststroke pain syndromes and chronic facial pain syndromes. Rates of reported efficacy for these procedures vary widely, ranging from 12% to 60%. The U.S. Food and Drug Administration (FDA) initially approved and then rescinded the approval of DBS for pain.

The clinically significant complications of DBS take the form of surgical complications, hardware-related complications, and stimulation-dependent complications.3 Surgical complications of DBS surgery include intracranial hemorrhage and electrode misplacement. Hardware-related complications include electrode fracture, electrode erosion, and infection. Stimulation-dependent complications are the effect of undesired modulation of neural circuits adjacent to the targets of neuromodulation.

Surgical Complications and Avoidance

Intracranial Hemorrhage

Symptomatic intracranial hemorrhage is the most feared complication of DBS surgery, with an incidence of approximately 1% of patients undergoing DBS surgery. A number of source factors may influence hemorrhage rates. Bleeding may occur because of direct trauma at the brain surface; injury to vessels in cortical sulci; or injury to deeper vascular-rich structures such as the ependymal surface, the choroid plexus, or friable target regions.

During surgery, careful planning is performed to avoid traversing cortical sulci because of the presence of vessels in the subarachnoid space. If the planned trajectory traverses the ventricles, the surgeon is obliged to determine that the electrode path does not pass through the location of large veins, such as the thalamostriate veins, which are located along the caudate head, or through well-vascularized structures such as the choroid plexus. Disruption of the ependymal surface through a trajectory that skims the surface of the ventricle over a distance may also be a source of intraventricular hemorrhage.

In the author’s center, multiple steps are taken to minimize the risk of hemorrhage. Meticulous surgical planning is performed to plan both entry points and trajectories for DBS placement, as outlined above. Verification of positioning is performed with the minimum number of microelectrode passages, as rates of hemorrhage are believed to scale with approximately 0.2% per electrode track. Systolic blood pressure is carefully monitored and routinely maintained below 150 mm Hg. For patients taking chronic antithrombolytic therapies, aspirin and Coumadin are halted 1 week before DBS lead placement and remain off until 1 week after DBS placement.

Venous Infarction and Air Embolism

Venous infarction with delayed hemorrhage is another potential complication of DBS surgery. Burr holes for DBS are placed in close proximity to the midline in the region of the coronal suture, where large cortical veins often enter the superior sagittal sinus. Disruption of these vessels or inadvertent cauterization of large veins may lead to compromised venous drainage, venous engorgement, hemorrhage, or venous infarction.

A second form of venous complication during surgery is venous air embolism. DBS surgery is most often performed in a sitting position, with the cranial opening above the level of the heart. As a result, a potential for venous air embolism exists. The rate of asymptomatic and symptomatic air embolism is not known, although coughing and transient cardiovascular changes are occasionally observed in DBS surgery.

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