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Dorsal Column Mapping via Phase Reversal Method: The Refined Technique and Clinical Applications

Nair, Dinesh MD, PhD*; Kumaraswamy, Vishakhadatta M. MD*,§; Braver, Diana*; Kilbride, Ronan D. MD*; Borges, Lawrence F. MD; Simon, Mirela V. MD, MSc*

doi: 10.1227/NEU.0000000000000287
Concepts, Innovations and Techniques
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BACKGROUND: Safe resection of intramedullary spinal cord tumors can be challenging, because they often alter the cord anatomy. Identification of neurophysiologically viable dorsal columns (DCs) and of neurophysiologically inert tissue, eg, median raphe (MR), as a safe incision site is crucial for avoiding postoperative neurological deficits. We present our experience with and improvements made to our previously described technique of DC mapping, successfully applied in a series of 12 cases.

OBJECTIVE: To describe a new, safe, and reliable technique for intraoperative DC mapping.

METHODS: The right and left DCs were stimulated by using a bipolar electric stimulator and the triggered somatosensory evoked potentials recorded from the scalp. Phase reversal and amplitude changes of somatosensory evoked potentials were used to neurophysiologically identify the laterality of DCs, the inert MR, as well as other safe incision sites.

RESULTS: The MR location was neurophysiologically confirmed in all patients in whom this structure was first visually identified as well as in those in whom it was not, with 1 exception. DCs were identified in all patients, regardless of whether they could be visually identified. In 3 cases, negative mapping with the use of this method enabled the surgeon to reliably identify additional inert tissue for incision. None of the patients had postoperative worsening of the DC function.

CONCLUSION: Our revised technique is safe and reliable, and it can be easily incorporated into routine intramedullary spinal cord tumor resection. It provides crucial information to the neurosurgeon to prevent postoperative neurological deficits.

ABBREVIATIONS: DC, dorsal column

DCM, dorsal column mapping

MR, median raphe

SSEP, somatosensory evoked potential

*Neurophysiology Division, Department of Neurology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts;

Department of Neurosurgery, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts;

§Department of Neurology, Case Western Reserve University, Cleveland, Ohio

Correspondence: Mirela Simon, MD, WACC 739-G, Massachusetts General Hospital, 55 Fruit St, Boston, MA 02114. E-mail:

Received August 28, 2013

Accepted January 02, 2014

Copyright © by the Congress of Neurological Surgeons