Bio

Bio


Dr. Parker is currently completing an in-folded fellowship in Adult and Pediatric Epilepsy Surgery at Stanford and Lucile Packard Children's Hospital under the mentorship of Dr. Gerald Grant, Dr. Casey Halpern, Dr. Jaimie Henderson, and Dr. Lawrence Shuer. As a resident at Stanford, he has focused his training and research on minimally invasive treatments for epilepsy and movement disorders. He has focused his training to develop clinical expertise in open microsurgical resection techniques, laser interstitial thermal therapy (LITT), focused ultrasound (MRgFUS), Deep Brain Stimulation (DBS), Responsive Neurostimulation (RNS), electrocorticography (ECoG), stereo-electro-encephalography (SEEG), and robotic-assisted surgery. At Stanford guided by his surgical mentors, Dr. Parker has utilized state of the art approaches to improve epilepsy surgery by combing SEEG, 3D models, whole brain tractography, and navigated operative exoscopes to guide safe surgical resections of epileptic foci.

Dr. Parker's research revolves around optimizing SEEG techniques for intracranial evaluation of epileptic foci and clinically-relevant brain mapping via understanding the role of white matter in seizure propagation. After residency, Dr. Parker plans to pursue fellowship training in Pediatric Neurosurgery.

Clinical Focus


  • Adult and Pediatric Epilepsy
  • Stereo-electro-encephalography (SEEG)
  • Adult and Pediatric Movement Disorders
  • Deep Brain Stimulation (DBS)
  • Responsive Neurostimulation (RNS)
  • Electrocorticography (ECoG)
  • Brain Mapping (awake craniotomy)
  • Microsurgical Resection (epileptic focus, temporal lobectomy, callosotomy, hemispehectomy, and disconnection procedures)
  • Neuro-Oncology
  • Tumor Associated Epilepsy
  • Residency

Honors & Awards


  • Henry Newman Award, Best Clinical Paper, San Francisco Neurological Society (2017)
  • Alden Harken Basic Science Research Award, University of Colorado, Department of Surgery (2015)
  • Inductee, Alpha Omega Alpha (2015)
  • Christopher G Reed Biologist Award, Dartmouth College, Department of Biology (2008)

Professional Education


  • AB, Dartmouth College, Biology with High Honors (2008)
  • PhD, University of Colorado, Anschutz Medical Campus, Cancer Biology (2013)
  • MD, University of Colorado, School of Medicine, Medicine (2015)

Research & Scholarship

Current Research and Scholarly Interests


Improving seizure network mapping to improve efficacy of epilepsy surgery

Current Clinical Interests


  • Adult and Pediatric Epilepsy Surgery
  • Adult and Pediatric Movement Disorders

Research Projects


  • Novel Methods of Stereo-Electro-Encephalograpy (SEEG) analysis for optimization of seizure onset zone localization

    Location

    Stanford, CA, USA

    Organization

    Stanford / Lucile Packard Children's Hospital (LPCH)

  • Neocortical Responsive Neurostimulation (RNS) for Medically-Refractory Adult Epilepsy

    Location

    Stanford, CA, USA

    Organization

    Stanford / Neuro Pace

  • Intratumoral Hetereogenity of Tumor Cell Invasion in Human Glioblastoma

    Intratumoral genetic heterogeneity is a widely accepted characteristic of human cancer, including the most common primary malignant brain tumor, glioblastoma. However, the variability in biological behaviors amongst cells within individual tumors leads to resistance to targeted therapies. Invasion into unaffected brain parenchyma is a leading mechanism of tumor recurrence unaddressed by the current therapeutic armamentarium. Further, providing insight into variability of tumor cell migration within individual tumors may inform discovery of novel anti-invasive therapeutics.

    To this end, we have developed and published on a novel ex vivo organotypic slice culture method to study the invasive behavior of human glioblastoma. With this technique, whole ex vivo cultures generated from EGFR-wild type and EGFR-amplified patient tumors can be treated with candidate therapeutic agents to evaluate potential sub-population restricted intratumoral drug-specific responses. We have recently shown through high-resolution time-lapse microscopy and quantitative path tracking that gefitinib treatment of cells in EGRR-amplified tumors significantly inhibits tumor cell migration.

    Location

    Stanford, CA, USA

    Organization

    University of Colorado / Inova Neuroscience Institute / Stanford University

    For More Information:

Publications

All Publications


  • Stereotactic laser ablation for completion corpus callosotomy. Journal of neurosurgery. Pediatrics Huang, Y., Yecies, D., Bruckert, L., Parker, J. J., Ho, A. L., Kim, L. H., Fornoff, L., Wintermark, M., Porter, B., Yeom, K. W., Halpern, C. H., Grant, G. A. 2019: 1?9

    Abstract

    Completion corpus callosotomy can offer further remission from disabling seizures when a prior partial corpus callosotomy has failed and residual callosal tissue is identified on imaging. Traditional microsurgical approaches to section residual fibers carry risks associated with multiple craniotomies and the proximity to the medially oriented motor cortices. Laser interstitial thermal therapy (LITT) represents a minimally invasive approach for the ablation of residual fibers following a prior partial corpus callosotomy. Here, the authors report clinical outcomes of 6 patients undergoing LITT for completion corpus callosotomy and characterize the radiological effects of ablation.A retrospective clinical review was performed on a series of 6 patients who underwent LITT completion corpus callosotomy for medically intractable epilepsy at Stanford University Medical Center and Lucile Packard Children's Hospital at Stanford between January 2015 and January 2018. Detailed structural and diffusion-weighted MR images were obtained prior to and at multiple time points after LITT. In 4 patients who underwent diffusion tensor imaging (DTI), streamline tractography was used to reconstruct and evaluate tract projections crossing the anterior (genu and rostrum) and posterior (splenium) parts of the corpus callosum. Multiple diffusion parameters were evaluated at baseline and at each follow-up.Three pediatric (age 8-18 years) and 3 adult patients (age 30-40 years) who underwent completion corpus callosotomy by LITT were identified. Mean length of follow-up postoperatively was 21.2 (range 12-34) months. Two patients had residual splenium, rostrum, and genu of the corpus callosum, while 4 patients had residual splenium only. Postoperative complications included asymptomatic extension of ablation into the left thalamus and transient disconnection syndrome. Ablation of the targeted area was confirmed on immediate postoperative diffusion-weighted MRI in all patients. Engel class I-II outcomes were achieved in 3 adult patients, whereas all 3 pediatric patients had Engel class III-IV outcomes. Tractography in 2 adult and 2 pediatric patients revealed time-dependent reduction of fractional anisotropy after LITT.LITT is a safe, minimally invasive approach for completion corpus callosotomy. Engel outcomes for completion corpus callosotomy by LITT were similar to reported outcomes of open completion callosotomy, with seizure reduction primarily observed in adult patients. Serial DTI can be used to assess the presence of tract projections over time but does not classify treatment responders or nonresponders.

    View details for DOI 10.3171/2019.5.PEDS19117

    View details for PubMedID 31374542

  • Intratumoral heterogeneity of endogenous tumor cell invasive behavior in human glioblastoma. Scientific reports Parker, J. J., Canoll, P., Niswander, L., Kleinschmidt-DeMasters, B. K., Foshay, K., Waziri, A. 2018; 8 (1): 18002

    Abstract

    Intratumoral genetic heterogeneity is a widely accepted characteristic of human cancer, including the most common primary malignant brain tumor, glioblastoma. However, the variability in biological behaviors amongst cells within individual tumors is not well described. Invasion into unaffected brain parenchyma is one such behavior, and a leading mechanism of tumor recurrence unaddressed by the current therapeutic armamentarium. Further, providing insight into variability of tumor cell migration within individual tumors may inform discovery of novel anti-invasive therapeutics. In this study, ex vivo organotypic slice cultures from EGFR-wild type and EGFR-amplified patient tumors were treated with the EGFR inhibitor gefitinib to evaluate potential sub-population restricted intratumoral drug-specific responses. High-resolution time-lapse microscopy and quantitative path tracking demonstrated migration of individual cells are punctuated by intermittent bursts of movement. Elevation of population aggregate mean speeds were driven by subpopulations of cells exhibiting frequent high-amplitude bursts, enriched within EGFR-amplified tumors. Treatment with gefitinib specifically targeted high-burst cell subpopulations only in EGFR-amplified tumors, decreasing bursting frequency and amplitude. We provide evidence of intratumoral subpopulations of cells with enhanced migratory behavior in human glioblastoma, selectively targeted via EGFR inhibition. These data justify use of direct human tumor slice cultures to investigate patient-specific therapies designed to limit tumor invasion.

    View details for PubMedID 30573757

  • A Human Glioblastoma Organotypic Slice Culture Model for Study of Tumor Cell Migration and Patient-specific Effects of Anti-Invasive Drugs JOVE-JOURNAL OF VISUALIZED EXPERIMENTS Parker, J. J., Lizarraga, M., Waziri, A., Foshay, K. M. 2017

    Abstract

    Glioblastoma (GBM) continues to carry an extremely poor clinical prognosis despite surgical, chemotherapeutic, and radiation therapy. Progressive tumor invasion into surrounding brain parenchyma represents an enduring therapeutic challenge. To develop anti-migration therapies for GBM, model systems that provide a physiologically relevant background for controlled experimentation are essential. Here, we present a protocol for generating slice cultures from human GBM tissue obtained during surgical resection. These cultures allow for ex vivo experimentation without passaging through animal xenografts or single cell cultures. Further, we describe the use of time-lapse laser scanning confocal microscopy in conjunction with cell tracking to quantitatively study the migratory behavior of tumor cells and associated response to therapeutics. Slices are reproducibly generated within 90 min of surgical tissue acquisition. Retrovirally-mediated fluorescent cell labeling, confocal imaging, and tumor cell migration analyses are subsequently completed within two weeks of culture. We have successfully used these slice cultures to uncover genetic factors associated with increased migratory behavior in human GBM. Further, we have validated the model's ability to detect patient-specific variation in response to anti-migration therapies. Moving forward, human GBM slice cultures are an attractive platform for rapid ex vivo assessment of tumor sensitivity to therapeutic agents, in order to advance personalized neuro-oncologic therapy.

    View details for PubMedID 28784966

  • Cost-effectiveness of focused ultrasound, radiosurgery, and DBS for essential tremor. Movement disorders Ravikumar, V. K., Parker, J. J., Hornbeck, T. S., Santini, V. E., Pauly, K. B., Wintermark, M., Ghanouni, P., Stein, S. C., Halpern, C. H. 2017

    Abstract

    Essential tremor remains a very common yet medically refractory condition. A recent phase 3 study demonstrated that magnetic resonance-guided focused ultrasound thalamotomy significantly improved upper limb tremor. The objectives of this study were to assess this novel therapy's cost-effectiveness compared with existing procedural options.Literature searches of magnetic resonance-guided focused ultrasound thalamotomy, DBS, and stereotactic radiosurgery for essential tremor were performed. Pre- and postoperative tremor-related disability scores were collected from 32 studies involving 83 magnetic resonance-guided focused ultrasound thalamotomies, 615 DBSs, and 260 stereotactic radiosurgery cases. Utility, defined as quality of life and derived from percent change in functional disability, was calculated; Medicare reimbursement was employed as a proxy for societal cost. Medicare reimbursement rates are not established for magnetic resonance-guided focused ultrasound thalamotomy for essential tremor; therefore, reimbursements were estimated to be approximately equivalent to stereotactic radiosurgery to assess a cost threshold. A decision analysis model was constructed to examine the most cost-effective option for essential tremor, implementing meta-analytic techniques.Magnetic resonance-guided focused ultrasound thalamotomy resulted in significantly higher utility scores compared with DBS (P < 0.001) or stereotactic radiosurgery (P < 0.001). Projected costs of magnetic resonance-guided focused ultrasound thalamotomy were significantly less than DBS (P < 0.001), but not significantly different from radiosurgery.Magnetic resonance-guided focused ultrasound thalamotomy is cost-effective for tremor compared with DBS and stereotactic radiosurgery and more effective than both. Even if longer follow-up finds changes in effectiveness or costs, focused ultrasound thalamotomy will likely remain competitive with both alternatives. 2017 International Parkinson and Movement Disorder Society.

    View details for DOI 10.1002/mds.26997

    View details for PubMedID 28370272

  • Frontal and occipital horn ratio is associated with multifocal intraparenchymal hemorrhages in neonatal shunted hydrocephalus. Journal of neurosurgery. Pediatrics Oushy, S., Parker, J. J., Campbell, K., Palmer, C., Wilkinson, C., Stence, N. V., Handler, M. H., Mirsky, D. M. 2017; 20 (5): 432?38

    Abstract

    OBJECTIVE Placement of a cerebrospinal fluid diversion device (i.e., shunt) is a routine pediatric neurosurgical procedure, often performed in the first weeks of life for treatment of congenital hydrocephalus. In the postoperative period, shunt placement may be complicated by subdural, catheter tract, parenchymal, and intraventricular hemorrhages. The authors observed a subset of infants and neonates who developed multifocal intraparenchymal hemorrhages (MIPH) following shunt placement and sought to determine any predisposing perioperative variables. METHODS A retrospective review of the electronic medical record at a tertiary-care children's hospital was performed for the period 1998-2015. Inclusion criteria consisted of shunt placement, age < 30 days, and available pre- and postoperative brain imaging. The following data were collected and analyzed for each case: ventricular size ratios, laboratory values, clinical presentation, shunt and valve type, and operative timing and approach. RESULTS A total of 121 neonates met the inclusion criteria for the study, and 11 patients (9.1%) had MIPH following shunt placement. The preoperative frontal and occipital horn ratio (FOR) was significantly higher in the patients with MIPH than in those without (0.65 vs 0.57, p < 0.001). The change in FOR (?FOR) after shunt placement was significantly greater in the MIPH group (0.14 vs 0.08, p = 0.04). Among neonates who developed MIPH, aqueductal stenosis was the most common etiology (45%). The type of shunt valve was associated with incidence of MIPH (p < 0.001). Preoperative clinical parameters, including head circumference, bulging fontanelle, and coagulopathy, were not significantly associated with development of MIPH. CONCLUSIONS MIPH represents an underrecognized complication of neonatal shunted hydrocephalus. Markers of severity of ventriculomegaly (FOR) and ventricular response to CSF diversion (?FOR) were significantly associated with occurrence of MIPH. Choice of shunt and etiology of hydrocephalus were also significantly associated with MIPH. After adjusting for corrected age, etiology of hydrocephalus, and shunt setting, the authors found that ?FOR after shunting was still associated with MIPH. A prospective study of MIPH prevention strategies and assessment of possible implications for patient outcomes is needed.

    View details for PubMedID 28885094

  • Vocal Tremor: Novel Therapeutic Target for Deep Brain Stimulation. Brain sciences Ravikumar, V. K., Ho, A. L., Parker, J. J., Erickson-DiRenzo, E., Halpern, C. H. 2016; 6 (4)

    Abstract

    Tremulous voice is characteristically associated with essential tremor, and is referred to as essential vocal tremor (EVT). Current estimates suggest that up to 40% of individuals diagnosed with essential tremor also present with EVT, which is associated with an impaired quality of life. Traditional EVT treatments have demonstrated limited success in long-term management of symptoms. However, voice tremor has been noted to decrease in patients receiving deep brain stimulation (DBS) with the targeting of thalamic nuclei. In this study, we describe our multidisciplinary procedure for awake, frameless DBS with optimal stimulation targets as well as acoustic analysis and laryngoscopic assessment to quantify tremor reduction. Finally, we investigate the most recent clinical evidence regarding the procedure.

    View details for PubMedID 27735866

  • Gefitinib selectively inhibits tumor cell migration in EGFR-amplified human glioblastoma. Neuro-oncology Parker, J. J., Dionne, K. R., Massarwa, R., Klaassen, M., Foreman, N. K., Niswander, L., Canoll, P., Kleinschmidt-Demasters, B. K., Waziri, A. 2013; 15 (8): 1048?57

    Abstract

    Tissue invasion is a hallmark of most human cancers and remains a major source of treatment failure in patients with glioblastoma (GBM). Although EGFR amplification has been previously associated with more invasive tumor behavior, existing experimental models have not supported quantitative evaluation of interpatient differences in tumor cell migration or testing of patient-specific responses to therapies targeting invasion. To explore these questions, we optimized an ex vivo organotypic slice culture system allowing for labeling and tracking of tumor cells in human GBM slice cultures.With use of time-lapse confocal microscopy of retrovirally labeled tumor cells in slices, baseline differences in migration speed and efficiency were determined and correlated with EGFR amplification in a cohort of patients with GBM. Slices were treated with gefitinib to evaluate anti-invasive effects associated with targeting EGFR.Migration analysis identified significant patient-to-patient variation at baseline. EGFR amplification was correlated with increased migration speed and efficiency compared with nonamplified tumors. Critically, gefitinib resulted in a selective and significant reduction of tumor cell migration in EGFR-amplified tumors.These data provide the first identification of patient-to-patient variation in tumor cell migration in living human tumor tissue. We found that EGFR-amplified GBM are inherently more efficient in their migration and can be effectively targeted by gefitinib treatment. These data suggest that stratified clinical trails are needed to evaluate gefitinib as an anti-invasive adjuvant for patients with EGFR-amplified GBM. In addition, these results provide proof of principle that primary slice cultures may be useful for patient-specific screening of agents designed to inhibit tumor invasion.

    View details for DOI 10.1093/neuonc/not053

    View details for PubMedID 23749785

    View details for PubMedCentralID PMC3714155

  • Preoperative evaluation of pineal tumors. Neurosurgery clinics of North America Parker, J. J., Waziri, A. 2011; 22 (3): 353?58, vii-viii

    Abstract

    The role of the neurosurgeon is critical for initiating preoperative evaluation and care for pineal region tumors. Preoperative evaluation of pineal region tumor can be simplified into a checklist: (1) evaluation for emergent surgical intervention due to symptomatic obstructive hydrocephalus or mass effect; (2) development of a focused differential after acquisition of craniospinal MRI, serum and cerebrospinal fluid oncoprotein levels, and cerebrospinal fluid cytology; and (3) decision on whether a biopsy, surgical resection, or both are necessary. Subsequent biopsy or surgical resection is the first step of tumor management and leads to coordination of consultation with medical and radiation oncology.

    View details for DOI 10.1016/j.nec.2011.04.003

    View details for PubMedID 21801983

Footer Links:

Stanford Medicine Resources: