What is IONM?

Intraoperative Neuromonitoring (IONM) assesses the functional integrity of the brain, spinal cord and peripheral nerves during procedures involving these neural structures. IONM monitoring can assist in neurosurgical, ortho-spine, and neurovascular procedures by informing the surgeons of the neurological function of the patient’s central and peripheral nervous systems while under anesthesia.

What procedures can IOM assist with?

Intraoperative Neuromonitoring is ideal for assessing neurological function in the following surgeries:

Neurosurgical Procedures

  • Craniotomies for Tumor Removal
  • Spinal Cord Neoplasms
  • Spinal Discectomies
  • Spinal Laminectomies
  • Intra/extra-medullary spinal cord tumors
  • Peripheral Nerve Injury
  • Brachial Plexus Nerve Injury
  • Instrumentation
  • Posterior Fossa Decompression for Arnold Chiari Malformation
  • Acoustic Neuroma/Vestibular Schwannoma
  • Skull-Based Tumors
  • Sensorimotor Cortex Mapping


  • Thyroidectomy
  • Tympanoplasty
  • Stapedectomy

Orthopedic Procedures

  • Scoliosis
  • Spinal Laminectomies
  • Spinal Discectomies
  • Spinal Fusions
  • Spinal Instrumentation
  • Acetabular Fractures and Revisions
  • Hip Lengthening and Replacements

Neurovascular Procedures

  • Arteriovenous Malformation
  • Aneurysms
  • Microvascular Decompression
  • Thoracoabdominal Aneurysms
  • Carotid Endartectomies

What tests and modalities do we perform?

SSEPs – Somatosensory Evoked Potentials – SSEPs monitor the functional integrity of the sensory (or feeling) nerve pathways, sending small stimulations along the nerves in the arms and legs and recording the strength and timing of the signals as they travel up the spinal cord to the brain. SSEPs are used most often to monitor the dorsal (posterior) columns of the spinal cord during spine surgery but can also be used during specified brain and peripheral nerve surgeries.

TcMEPs – Transcranial Motor Evoked Potentials – TcMEPs monitor the functional integrity of the motor (or movement) nerve pathways. While under anesthesia, a mild electrical current is applied across the motor cortex of the brain to stimulate a response in specific muscles. The muscle’s responses are recorded and monitored to ensure that the signal traveling along the motor pathways is not interrupted.

BAEPs or ABRs – Brainstem Auditory Evoked Potentials / Auditory Brainstem Responses : BAEPs record the brainstem’s response to an auditory stimulus by monitoring the functional status of the auditory nerve. This modality is used to monitor brainstem function and to help preserve hearing in acoustic neuroma and brainstem tumor cases. BAEPs are performed by recording the brainstem’s response to a series of clicks delivered separately to each ear from small earphones inserts, similar to foam earplugs. The responses are monitored to identify potential risk to the auditory nerve or brainstem and help prevent permanent damage.

EMG – Electromyography : EMG monitoring can give the surgeon immediate feedback of nerve root irritation by recording electrical activity and fasciculations, or micro-vibrations, occurring in the corresponding muscle groups. The recorded responses are monitored to identify potential risk to the nerve root and help prevent permanent damage. Evoked or Triggered EMG (tEMG), the response to an electrical stimulus delivered by the surgeon through a hand-held probe, is also used to identify and test neural structures.

Pedicle Screw Stimulation is a Triggered EMG technique obtained by stimulating a screw placed in the pedicle of a vertebra. As a nerve root lies immediately beneath each pedicle, a response obtained at too low a stimulus intensity level indicates a breach in the bone. This modality is used to avoid nerve root damage caused by such a breach. Some of the procedures for which we provide pedicle screw stimulation include scoliosis correction and instrumentation for spinal instability.

Cranial Nerve Monitoring is used to protect cranial nerves during surgical procedures. Cranial nerves are particularly susceptible to damage by mechanical trauma or ischemia during intracranial and extracranial surgery. Research and clinical experience indicate that the use of cranial nerve monitoring can prevent or reduce neurological injuries associated with surgery.

EEG – Electroencephalogram: EEGs record spontaneous brain activity in order to monitor functional integrity of the cerebral cortex, specifically to avoid injuries caused by ischemia during procedures such as carotid endarterectomies and aneurysm clippings.