Intraoperative microelectrode recording

Intraoperative microelectrode recording

Microelectrode recording (MER) is used to confirm targeting accuracy during deep brain stimulation (DBS) surgery.

While the efficacy of deep brain stimulation (DBS) to treat various neurological disorders is undisputed, the surgical methods differ widely and the importance of intraoperative microelectrode recording (MER) or macrostimulation (MS) remains controversially debated 1).

At many centers around the world that treat movement disorders, the gold standard for optimally targeting the sensorimotor area of the STN currently relies on microelectrode recording (MER) of single and multi-neuron activity traversing the planned surgical trajectories.

see HaGuide Tool.

When extracellular microelectrodes (tens of microns in diameter) are placed within the brain, they record the extracellular electric field generated by multiple nearby spiking neurons. This is the basis of the microelectrode recording technique used daily by many functional neurosurgeons, and is core to the development of various brain computer interfaces.

The functional regions clustering through microelectrode recording (MER) is a critical step in deep brain stimulation (DBS) surgery. The localization of the optimal target highly relies on the neurosurgeon’s empirical assessment of the neurophysiological signal. This work presents an unsupervised clustering algorithm to get the optimal cluster result of the functional regions along the electrode trajectory.

The dataset consists of the MERs obtained from the routine bilateral DBS for PD patients. Several features have been extracted from MER and divided into groups based on the type of neurophysiological signal. We selected single feature groups rather than all features as the input samples of each division of the divisive hierarchical clustering (DHC) algorithm. And the optimal cluster result has been achieved through a feature group combination selection (FGS) method based on genetic algorithm (GA). To measure the performance of this method, we compared the accuracy and validation indexes of three methods, including DHC only, DHC with GA-based FGS and DHC with GA-based feature selection (FS) in other studies, on the universal and DBS datasets.

Results show that the DHC with GA-based FGS achieved the optimal cluster result compared with other methods. The three borders of the STN can be identified from the cluster result. The dorsoventral sizes of the STN and dorsal STN are 4.45 mm and 2.02 mm. In addition, the features extracted from the multiunit activity, background unit activity and local field potential are found to be the most representative feature groups to identify the dorsal, d-v and ventral borders of the STN, respectively.

The clustering algorithm showed a reliable performance of the automatic identification of functional regions in DBS. The findings can provide valuable assistance for both neurosurgeons and stereotactic surgical robots in DBS surgery 2).

It is unclear which magnetic resonance imaging (MRI) sequence most accurately corresponds with the electrophysiological subthalamic nucleus (STN) obtained during microelectrode recording (MER, MER-STN). CT/MRI fusion allows for comparison between MER-STN and the STN visualized on preoperative MRI (MRI-STN).

Kochanski et al. describe a technique using intraoperative computed tomography (CT) extrapolation (iCTE) to predetermine and adjust the trajectory of the guide tube to improve microelectrode targeting accuracy. They hypothesized that this technique would decrease the number of MER tracks and operative time, while increasing the recorded length of the subthalamic nucleus (STN) 3).

Case series

Krauss et al. included 101 patients who underwent awake bilateral implantation of electrodes in the subthalamic nucleus with microelectrode recording (MER) and macrostimulation (MS) for Parkinson’s disease from 2009 to 2017 in a retrospective observational study. They analyzed intraoperative motor outcomes between anatomically planned stimulation point (PSP) and definite stimulation point (DSP), lead adjustments, and Unified Parkinson’s Disease Rating Scale Item III (UPDRS-III), levodopa equivalent daily dose (LEDD), and adverse events (AE) after 6 months.

They adjusted 65/202 leads in 47/101 patients. In adjusted leads, MS results improved significantly when comparing PSP and DSP (p < 0.001), resulting in a number needed to treat of 9.6. After DBS, UPDRS-III and LEDD improved significantly after 6 months in adjusted and nonadjusted patients (p < 0.001). In 87% of leads, the active contact at 6 months still covered the optimal stimulation point during surgery. In total, 15 AE occurred.

MER and MS have a relevant impact on the intraoperative decision of final lead placement and prevent a substantial rate of poor stimulation outcome. The optimal stimulation points during surgery and chronic stimulation strongly overlap. Follow-up UPDRS-III results, LEDD reductions, and DBS-related AE correspond well to previously published data 4).

The precision and accuracy of direct targeting with quantitative susceptibility mapping (QSM) was examined in a total of 25 Parkinson’s disease patients between 2013 and 2015 at the Department of Neurosurgery, Mount Sinai Health System, New York. QSM was utilized as the primary magnetic resonance imaging (MRI) method to perform direct STN targeting on a stereotactic planning station utilizing computed tomography/MR fusion. Intraoperative microelectrode recordings (MER) were obtained to confirm appropriate trajectory through the sensorimotor STN.

Estimations of STN thickness between the MER and QSM methods appeared to be correlated. Mean STN thickness was 5.3 mm. Kinesthetic responsive cells were found in > 90% of electrode runs. The mean radial error (±SEM) was 0.54 ± 0.1 mm. Satisfactory clinical response as determined by Unified Parkinson’s Disease Rating Scale (UPDRS III) was seen at 12 mo after surgery.

Direct targeting of the sensorimotor STN using QSM demonstrates MER correlation and can be safely used for deep brain stimulation lead placement with satisfactory clinical response. These results imply that targeting based on QSM signaling alone is sufficient to obtain reliable and reproducible outcomes in the absence of physiological recordings 5).

In their analysis, Rasouli et al accept that the raw measurements they derived by the 2 methods (microelectrode recording [MER] vs quantitaive susceptibility mapping [QSM]) do not exhibit a high degree of correlation. They offer several reasons for this (differences in resolution, standard deviations, and narrow range of measurements), thereby justifying the use of normalized data and the Bland–Altman analysis. In contrast to the Bland–Altman analysis, which suggests agreement, the intra-correlation coefficient (ICC) = 0.12 implies that there is high variability between QSM and MER measurements within an individual (ie, they are not in good agreement). More useful in our view would be to see how well the actual measurements made with the 2 methods agree on a case by case basis. How often do the measurements agree within 0.1, 0.5, 1, 2 mm, etc.? Such valuable information would allow the readers to decide for themselves whether a measured subthalamic nucleus (STN) span on QSM is a legitimate proxy for the gold standard of measuring the STN with MER and we urge the authors to publish this data in a subsequent letter 6).


1) , 4)

Krauss P, Oertel MF, Baumann-Vogel H, Imbach L, Baumann CR, Sarnthein J, Regli L, Stieglitz LH. Intraoperative Neurophysiologic Assessment in Deep Brain Stimulation Surgery and its Impact on Lead Placement. J Neurol Surg A Cent Eur Neurosurg. 2020 Oct 13. doi: 10.1055/s-0040-1716329. Epub ahead of print. PMID: 33049794.

Cao L, Jie L, Zhou Y, Liu Y, Liu H. Automatic feature group combination selection method based on GA for the functional regions clustering in DBS. Comput Methods Programs Biomed. 2019 Sep 23;183:105091. doi: 10.1016/j.cmpb.2019.105091. [Epub ahead of print] PubMed PMID: 31590098.

Kochanski RB, Bus S, Pal G, Metman LV, Sani S. Optimization of Microelectrode Recording in Deep Brain Stimulation Surgery Using Intraoperative Computed Tomography. World Neurosurg. 2017 Jul;103:168-173. doi: 10.1016/j.wneu.2017.04.003. Epub 2017 Apr 10. PubMed PMID: 28408262.

Rasouli J, Ramdhani R, Panov FE, Dimov A, Zhang Y, Cho C, Wang Y, Kopell BH. Utilization of Quantitative Susceptibility Mapping for Direct Targeting of the Subthalamic Nucleus During Deep Brain Stimulation Surgery. Oper Neurosurg (Hagerstown). 2018 Apr 1;14(4):412-419. doi: 10.1093/ons/opx131. PubMed PMID: 28531270.

Alterman RL, Fleishman A, Ngo L. In Reply: Commentary: Utilization of Quantitative Susceptibility Mapping for Direct Targeting of the Subthalamic Nucleus During Deep Brain Stimulation Surgery. Oper Neurosurg (Hagerstown). 2018 Jul 13. doi: 10.1093/ons/opy139. [Epub ahead of print] PubMed PMID: 30011048.

Intraoperative Ultrasound for Spine Surgery

Intraoperative Ultrasound for Spine Surgery

Accurate and efficient registration of pre-operative computed tomography or magnetic resonance images with iUS images are key elements in the success of iUS-based spine navigation. While widely investigated in research, iUS-based spine navigation has not yet been established in the clinic. This is due to several factors including the lack of a standard methodology for the assessment of accuracy, robustness, reliability, and usability of the registration method. To address these issues, Gueziri et al. presented a systematic review of the state-of-the-art techniques for iUS-guided registration in spinal image guided surgery (IGS). The review follows a new taxonomy based on the four steps involved in the surgical workflow that include pre-processing, registration initialization, estimation of the required patient to image transformation, and a visualization process. They provided a detailed analysis of the measurements in terms of accuracy, robustness, reliability, and usability that need to be met during the evaluation of a spinal IGS framework. Although this review is focused on spinal navigation, they expect similar evaluation criteria to be relevant for other IGS applications 1).

Intraoperative ultrasound (iUS) has been applied in spinal surgery for all kinds of diseases 2) 3) ranging from trauma, 4) degenerative diseases, 5) 6) developmental malformations, 7) vascular diseases, 8). to imaging in spinal tumor surgery

Intraoperative Ultrasound for spinal tumor surgery

Intraoperative Ultrasound for spinal tumor surgery


Intraoperative ultrasound is often helpful for:

a) localizing the cyst

b) assessing for septations (to avoid shunting only part of cyst)

Controversial,for intramedullary spinal cord tumors 9) favored by some experts. Astrocytomas are usually iso-echoic with the spinal cord, whereas ependymomas are usually hyperechoic.

Transpedicular thoracic discectomy

Intraoperative ultrasound is a simple yet valuable tool for real-time imaging during transpedicular thoracic discectomy. Visualization provided by intraoperative US increases the safety profile of posterior approaches and may make thoracotomy unnecessary in a selected group of patients, especially when a patient has existing pulmonary disease or is otherwise not medically fit for the transthoracic approach 10) 11).



Gueziri HE, Santaguida C, Collins DL. The state-of-the-art in ultrasound-guided spine interventions [published online ahead of print, 2020 Jun 26]. Med Image Anal. 2020;65:101769. doi:10.1016/

Ganau M, Syrmos N, Martin AR, Jiang F, Fehlings MG. Intraoperative ultrasound in spine surgery: history, current applications, future developments. Quant Imaging Med Surg. 2018;8: 261-267.

Vasudeva VS, Abd-El-Barr M, Pompeu YA, Karhade A, Groff MW, Lu Y. Use of intraoperative ultrasound during spinal surgery. Glob Spine J. 2017;7:648-656.

Meinig H, Doffert J, Linz N, Konerding MA, Gercek E, Pitzen T. Sensitivity and specificity of ultrasound in spinal trauma in 29 consecutive patients. Eur Spine J. 2015;24:864-870.

Nishimura Y, Thani NB, Tochigi S, Ahn H, Ginsberg HJ. Thoracic discectomy by posterior pedicle-sparing, transfacet approach with realtime intraoperative ultrasonography: clinical article. J Neurosurg Spine. 2014;21:568-576.

Goodkin R, Haynor DR, Kliot M. Intraoperative ultrasound for monitoring anterior cervical vertebrectomy. Technical note. J Neurosurg. 1996;84: 702-704.

. Cui LG, Jiang L, Zhang HB, et al. Monitoring of cerebrospinal fluid flow by intraoperative ultrasound in patients with Chiari I malformation. Clin Neurol Neurosurg. 2011;113:173-176.

Prada F, Del Bene M, Farago G, DiMeco F. Spinal dural arteriovenous fistula: is there a role for intraoperative contrast-enhanced ultrasound? World Neurosurg. 2017;100:712.e15-712.e18.

Albright AL. Pediatric Intramedullary Spinal Cord Tumors. Childs Nerv Syst. 1999; 15:436–437

Tan LA, Lopes DK, Fontes RB. Ultrasound-guided posterolateral approach for midline calcified thoracic disc herniation. J Korean Neurosurg Soc. 2014 Jun;55(6):383-6. doi: 10.3340/jkns.2014.55.6.383. Epub 2014 Jun 30. PubMed PMID:25237439.

Nishimura Y, Thani NB, Tochigi S, Ahn H, Ginsberg HJ. Thoracic discectomy by posterior pedicle-sparing, transfacet approach with real-time intraoperative ultrasonography. J Neurosurg Spine. 2014 Jul 18:1-9. [Epub ahead of print] PubMed PMID: 25036220.

Intraoperative ultrasound for intradural spinal tumor

Intraoperative ultrasound for intradural spinal tumor

Intraoperative ultrasound is a valuable tool to detect spinal tumors, evaluate the surgical approach and plan the surgical strategy considering the position and relationships of the lesion with bony, neural and vascular structures 1).

Surgeons should consider the use of intraoperative ultrasound when approaching intradural spinal tumor or when addressing pathology ventral to the thecal sac via a posterior approach 2).

Three-dimensional intraoperative ultrasound for intradural spinal tumor

see Three-dimensional intraoperative ultrasound for intradural spinal tumor

In 69 intradural spinal tumors, operated on between 2012 and 2016. A 5-8 MHz probe of IOUSG was used, before and after durotomy to perform the exact durotomy and myelotomy, and after tumor resection, to detect a residual tumor. A retrospective review of parameters including demographic data, localization, and histopathology of the tumor, IOUSG findings, and the amount of tumor resection was made.

In a total of 69 intradural spinal tumors (42 extramedullary, and 27 intramedullary tumors) IOUSG was used during surgery. Total excision was performed in 68 cases, and subtotal excision in one case. Pre-durotomy IOUSG showed sufficient laminectomy in 62 cases. In 7 cases, as the IOUSG failed to show all borders of the tumor, laminectomy was extended.

IOUSG is an important tool, which contributes to intradural spine surgery. This modality shows the tumor appearance before durotomy and is therefore helpful in deciding the amount of laminectomy and durotomy in addition to the exact location of myelotomy. It also provides the surgeon with information about residual tumor after excision, thereby increasing the safety and success of the surgical procedure 3).

From January to July 2016, Stefini et al. performed 10 navigated procedures for intradural spinal tumors by merging MRI and 3-D fluoro images. Nine patients had an intradural extramedullary tumor, 6 had neurinomas, and 3 had meningiomas; 1 patient had an intramedullary spinal cord metastasis. : The surgically demonstrated benefits of spinal navigation for the removal of intradural tumors include the decreased risk of surgery at the wrong spinal level, a minimal length of skin incision and muscle strip, and a reduction in bone removal extension. Furthermore, this technique offers the advantage of opening the dura as much as is necessary and, in the case of intrinsic spinal cord tumors, it allows the tumor to be centered. Otherwise, this would not be visible, thus enabling the precise level and the posterior midline sulcus to be determined when performing a mielotomy 4).

A total number of 158 intradural spinal lesions were operated on using iUS. Of these, 107 lesions (68%) were intradural extramedullary and 51 (32%) were intramedullary. All lesions were clearly visible using the ultrasound probe. The high-frequency linear probes (10-12 MHz) provided a better image quality compared with lower-frequency probes. Color and power-angiography modes were helpful in assessing the vascularization of the tumors and location of the major vessels in the vascular lesions.

Ivanov et al. documented how iUS was used to facilitate safe and efficient spinal tumor resection at each stage of the operation. iUS was beneficial in confirmation of tumor location and extension, planning myelotomy, and estimation of degree of resection of the intramedullary tumors. It was particularly helpful in guiding the approach in redo surgeries for recurrent spinal cord tumors.

iUS has a fast learning curve and offers additional intraoperative information that can help improve surgical accuracy and therefore may reduce procedure-related morbidity 5).

Twenty-six patients with intradural spinal cord tumors were surgically treated under intraoperative ultrasonographic guidance between January 2007 and May 2011. Guidance with IOUSG was used in 26 patients, of which 14 fourteen had extramedullary and 12 had intramedullary tumors. Intraoperative ultrasound assistance was used to localize each tumor exactly before opening the dura. The extent of tumor resection was verified using axial and sagittal sonographic views. The extent of tumor resection achieved with IOUSG guidance was assessed on postoperative early control MRI sections.

Total tumor resection was achieved in 22 (84%) of 26 cases. All of the residual tumors were typically intramedullary and infiltrative. The sensitivity of IOUSG for the determination of the extent of resection was found to be 92%. Ultrasonography was found to be effective in identification of tumor boundaries and protection of spinal cord vessels. The average time spent for IOUSG assessment was 7 minutes.

Intraoperative ultrasonography is practical, reliable and highly sensitive for spinal cord surgery. It not only enhances surgical orientation, but also reduces morbidity and helps to resect the tumor completely 6).

Between January 2006 and July 2007, 30 patients with suspected intradural spinal tumours underwent surgery with the aid of IOUS. There were 13 patients with intramedullary tumours (ependymoma=2, astrocytoma=5, hemangioblastoma=2 and metastasis=4); and 14 patients with extramedullary tumours (meningioma=6, neurinoma=6, filum terminale ependymoma=1 and lipoma=1). In 3 patients histopathology did not reveal any neoplasm despite an MRI suggesting tumour. Their sonographic features are analyzed and the advantages of IOUS are discussed.

The shape and expansion of intradural tumours could be visualized on IOUS. The sonographic visualization allowed adapting the approach to an appropriate location and size before dura opening. Certain sonographic features can be used for a differential diagnosis of different intradural tumours. In addition, IOUS can inform neurosurgeons about the location of the neoplastic tissue, its relation to the spinal cord and the size of residual tumour following excision.

IOUS is a sensitive intraoperative tool. When appropriately applied to assist surgical procedures, it offers additional intraoperative information that helps to improve surgical precision and therefore might reduce the procedure related morbidity 7).

From 1997 to 9/2002 32 patients with the diagnosis of an ependymoma (n = 9), astrocytoma (n = 5), haemangioblastoma (n = 5), neurinoma (n = 4), meningeoma (n = 4) and filum terminale ependymoma (n = 5) were investigated by intraoperative transdural sonography. The sonographic results were correlated to the preoperative MRI-findings and histopathological work-up.

Intramedullary tumours characteristically present with a heterogenous morphology, sometimes carrying intralesional or perilesional cysts. The tumour margins are frequently poorly defined, and there is a perifocal oedema. Extramedullary tumours frequently display a homogenous signal intensity, well defined tumour margins and the abscence of perifocal oedema. Haemangioblastomas turned out to be a specific sonographic entity among intramedullary tumours, as they most often contain only a cystic part with a small tumour nodule. IOUS influenced the surgical approach as laminotomy has to be extended in 7/32 cases to reach the tips of the tumour.

The precision of surgical exposure of intradural spinal lesions can be optimised by IOUS which shows a high correlation with MRI characterizing extra- and intramedullary tumours. Using IOUS, the exact position of the laminectomy/laminotomy can be adapted to the true extent of the tumour, thus avoiding the necessity of further bone work in the case of the frequently oedematous spinal cord protruding through the opening in the dura. Overall, IOUS guidance can help to reduce postoperative morbidity in surgery for all spinal intradural lesions 8).



Prada F, Vetrano IG, Filippini A, Del Bene M, Perin A, Casali C, Legnani F, Saini M, DiMeco F. Intraoperative ultrasound in spinal tumor surgery. J Ultrasound. 2014 Jun 7;17(3):195-202. doi: 10.1007/s40477-014-0102-9. eCollection 2014 Sep. PubMed PMID: 25177392; PubMed Central PMCID: PMC4142127.

Vasudeva VS, Abd-El-Barr M, Pompeu YA, Karhade A, Groff MW, Lu Y. Use of Intraoperative Ultrasound During Spinal Surgery. Global Spine J. 2017 Oct;7(7):648-656. doi: 10.1177/2192568217700100. Epub 2017 May 31. PubMed PMID: 28989844; PubMed Central PMCID: PMC5624373.

Haciyakupoglu E, Yuvruk E, Onen MR, Naderi S. The Use of Intraoperative Ultrasonography in Intradural Spinal Tumor Surgery. Turk Neurosurg. 2019;29(2):237-241. doi: 10.5137/1019-5149.JTN.23296-18.3. PubMed PMID: 30649794.

Stefini R, Peron S, Mandelli J, Bianchini E, Roccucci P. Intraoperative Spinal Navigation for the Removal of Intradural Tumors: Technical Notes. Oper Neurosurg (Hagerstown). 2018 Jul 1;15(1):54-59. doi: 10.1093/ons/opx179. PubMed PMID: 28962027.

Ivanov M, Budu A, Sims-Williams H, Poeata I. Using Intraoperative Ultrasonography for Spinal Cord Tumor Surgery. World Neurosurg. 2017 Jan;97:104-111. doi: 10.1016/j.wneu.2016.09.097. Epub 2016 Oct 3. PubMed PMID: 27713065.

Toktas ZO, Sahin S, Koban O, Sorar M, Konya D. Is intraoperative ultrasound required in cervical spinal tumors? A prospective study. Turk Neurosurg. 2013;23(5):600-6. doi: 10.5137/1019-5149.JTN.7199-12.1. PubMed PMID: 24101306.

Zhou H, Miller D, Schulte DM, Benes L, Bozinov O, Sure U, Bertalanffy H. Intraoperative ultrasound assistance in treatment of intradural spinal tumours. Clin Neurol Neurosurg. 2011 Sep;113(7):531-7. doi: 10.1016/j.clineuro.2011.03.006. Epub 2011 Apr 20. PubMed PMID: 21507563.

Regelsberger J, Langer N, Fritzsche E, Westphal M. [Intraoperative ultrasound of intra- and extramedullary tumours]. Ultraschall Med. 2003 Dec;24(6):399-403. German. PubMed PMID: 14658083.
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