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We help ensure your organization provides the highest level of neurological patient care.
Contact us to schedule a conversation about frequent procedures and modalities our physician oversight team can cover for your IONM or surgical needs.
Below is a list of the tests (modalities) most commonly interpreted by our physicians:
Somatosensory Evoked Potentials (SSEP): Somatosensory evoked responses are performed by placing an electrode on the skin or inserting a needle near the nerve being tested. This electrode delivers an electrical signal, and the response to that signal is measured at various points as it travels through the nervous system to the brain. This modality provides information about the integrity of the sensory pathways and has many uses, including spinal cord monitoring, detecting limb positioning problems, monitoring brainstem and cortical perfusion, and mapping sensory areas of the brain.
Electromyography (EMG): Electromyography is used to monitor nerves by recording activity in the muscles innervated by those nerves. This muscle activity can either be spontaneous (free-run EMG) or elicited by stimulating the nerve with a probe held by the surgeon (triggered or evoked EMG). EMG is performed by inserting tiny electrodes over specific muscles. If the nerve connected to the muscle is stimulated or irritated, an electrical signal travels to the muscle and makes the muscle contract. The recorded responses are monitored to identify potential risk to the nerve and help prevent permanent damage. Triggered EMG can be used to locate nervous tissue in the surgical field, test the integrity of nervous tissue, or test for safe placement of pedicle screws. Spontaneous and triggered EMG can be used to monitor spinal nerves and some of the cranial nerves.
Pedicle screw stimulation is triggered EMG obtained by stimulating a screw placed in the pedicle of a vertebra. As a nerve root lies immediately beneath each pedicle, an EMG response obtained at too low a stimulus intensity level indicates a breach or hole in the bone. This test modality is used to avoid nerve root damage caused by such a breach. Pedicle screw stimulation is routinely performed in scoliosis correction procedures and when instrumentation is placed for spinal instability.
Transcranial Motor Evoked Potentials (TcMEP): Transcranial motor evoked potentials are used to monitor the motor pathways in the spinal cord and brain. TcMEPs are performed by applying a mild electrical current across the motor cortex of the brain and recording responses in specific muscles. The muscle responses are recorded and monitored to ensure that the signal traveling through the motor pathways is not interrupted.
Brainstem Auditory Evoked Potentials (BAEPs): Brainstem auditory evoked potentials record the brainstem’s response to an auditory stimulus by monitoring the function of the auditory pathways. Responses are obtained by delivering click stimuli to each ear through small foam earphones inserted into the ear canal. The response to those clicks can be followed through the auditory pathway from the cochlea (inner ear) to the brainstem. Brainstem auditory evoked potentials are monitored to identify potential risk to the auditory nerve or brainstem and help prevent permanent damage.
Electroencephalography (EEG): Electroencephalography is used to monitor the function of the cerebral cortex of the brain. Electrodes are placed at several locations on the scalp to record ongoing brain activity. This provides immediate feedback about the function of cortical brain cells. Electroencephalography can be used in all types of surgeries but is most often used in vascular procedures to monitor blood flow to the brain. In cranial surgeries, the recording electrodes can also be placed directly on the exposed surface of the brain; this is called electrocorticography.
Cortical Mapping / Direct Cortical Stimulation: This is used to identify and map the sections of the brain generating seizures for epilepsy surgery, as well as the regions that are responsible for motor skills during tumor resection surgery. Cortical mapping of motor areas is performed by stimulating the designated areas of the brain with a very mild electrical current. As the motor areas are stimulated, muscle responses will be recorded in the part of the body that corresponds to that area of the motor cortex.
Phase reversal is a type of mapping that involves stimulating the upper extremities at the wrists (SSEPs, as described above) and recording from electrodes placed directly on the surface of the brain. A certain pattern of responses helps the surgeon locate the parts of the brain responsible for sensory versus motor function. This is helpful in tumor removal surgeries so that the surgeon can remove tumor without damaging areas of the brain that are responsible for movement.
Transcranial Doppler (TCD): This test measures the blood flow velocity in the internal arteries of the brain using an ultrasound beam. It is used to assess the risk of stroke and monitor cerebral blood flow in procedures such as cardiothoracic sugeries. TCD is done with electrodes placed on the skin on the temple, the base of the skull at the back of the neck, and over the closed eyelid. The clinician adjusts a probe to direct sound waves toward the blood vessels of interest, and the blood flow sounds in specific blood vessels are recorded and analyzed.
Cranial Nerve Monitoring: This testing is used to protect cranial nerves during surgery. Cranial nerves are particularly susceptible to damage by mechanical trauma and ischemia during intracranial and extracranial surgery. The use of cranial nerve monitoring can prevent or reduce neurological injuries associated with surgery. A number of reliable electrodiagnostic techniques have been adapted specifically to identify and evaluate cranial nerve function during surgery, including electromyography and nerve conduction studies.
Cranial nerve Electromyography (EMG): The evaluation of spontaneous and evoked electromyogenic activity can be extremely useful in monitoring cranial nerve function. Spontaneous EMG activity in the anatomical distribution of these nerves can signal irritation of the cranial nerve.
Compound Nerve Action Potential (CNAP): This test is used to monitor cranial or peripheral nerves using electrodes to record nerve activity at one location while the nerve is being electrically stimulated at another location. CNAP is used to assess the function of a nerve and can also be used to map or identify a lesion in the nerve. Frequent direct stimulation of the specific nerve enables the neuromonitoring team to assist the surgeon and prevent damage to the nervous structures.
Transcranial Cerebral Oximetry (TCCO): Transcranial cerebral oximetry is used to monitor changes in saturation of oxygen within a sample of blood in the cerebral cortex. Measurements are made by non-invasively transmitting and detecting low intensity, near-infrared light through electrodes placed on both sides of the patient's forehead. TCCO allows technologists to detect changes in the brain’s blood oxygen saturation which may require corrective action by the surgical team to prevent or reduce neurological injuries.