Samuel S. Shin

High-definition fiber tracking for assessment of neurological deficit in a case of traumatic brain injury: finding, visualizing, and interpreting small sites of damage

For patients with traumatic brain injury (TBI), current clinical imaging methods generally do not provide highly detailed information about the location of axonal injury, severity of injury, or expected recovery. In a case of severe TBI, the authors applied a novel high-definition fiber tracking (HDFT) to directly visualize and quantify the degree of axonal fiber damage and predict functional deficits due to traumatic axonal injury and loss of cortical projections. This 32-year-old man sustained a severe TBI. Computed tomography and MRI revealed an area of hemorrhage in the basal ganglia with mass effect, but no specific information on the location of axonal injury could be obtained from these studies. Examinations of the patient at Week 3 and Week 8 after TBI revealed motor weaknesses of the left extremities. Four months postinjury, 257-direction diffusion spectrum imaging and HDFT analysis was performed to evaluate the degree of axonal damage in the motor pathway and quantify asymmetries in the left and right axonal pathways. High-definition fiber tracking was used to follow corticospinal and corona radiata pathways from the cortical surface to the midbrain and quantify projections from motor areas. Axonal damage was then localized by assessing the number of descending fibers at the level of the cortex, internal capsule, and midbrain. The motor deficit apparent in the clinical examinations correlated with the axonal losses visualized using HDFT. Fiber loss estimates at 4 months postinjury accurately predicted the nature of the motor deficits (severe, focal left-hand weakness) when other standard clinical imaging modalities did not. A repeat scan at 10 months postinjury, when edema and hemorrhage had receded, replicated the fiber loss. Using HDFT, the authors accurately identified the presence and location of damage to the underlying white matter in this patient with TBI. Detailed information of injury provided by this novel technique holds future potential for precise neuroimaging assessment of TBI.

Detection of White Matter Injury in Concussion Using High-Definition Fiber Tractography

Over the last few decades, structural imaging techniques of the human brain have undergone significant strides. High resolution provided by recent developments in magnetic resonance imaging (MRI) allows improved detection of injured regions in patients with moderate-to-severe traumatic brain injury (TBI). In addition, diffusion imaging techniques such as diffusion tensor imaging (DTI) has gained much interest recently due to its possible utility in detecting structural integrity of white matter pathways in mild TBI (mTBI) cases. However, the results from recent DTI studies in mTBI patients remain equivocal. Also, there are important shortcomings for DTI such as limited resolution in areas of multiple crossings and false tract formation. The detection of white matter damage in concussion remains challenging, and development of imaging biomarkers for mTBI is still in great need. In this chapter, we discuss our experience with high-definition fiber tracking (HDFT), a diffusion spectrum imaging-based technique. We also discuss ongoing developments and specific advantages HDFT may offer concussion patients.

Early radiosurgery provides superior pain relief for trigeminal neuralgia patients

Objective: We evaluated factors associated with better outcomes after stereotactic radiosurgery (SRS) when it was performed as the first surgical procedure for medically refractory trigeminal neuralgia. Methods: A total of 121 patients (median age 72 years) with medically refractory pain and no prior surgery underwent Gamma Knife SRS as their initial surgical procedure for trigeminal neuralgia. Using a single 4-mm isocenter, patients received an average maximum dose of 80 Gy, delivered to the trigeminal nerve target defined by intraoperative MRI. The median follow-up was 36 months. Results: Pain relief (Barrow Neurological Institute [BNI] score I–IIIa) was achieved in 107 (88%) patients at a median time of 1 month. Patients who underwent earlier SRS (within 3 years of pain onset) had a shorter interval until pain relief (1 week, p < 0.001), had a longer interval of pain relief off medication (BNI-I, p < 0.001), and had a longer duration of adequate pain control (BNI-I–IIIa, p < 0.001). Median pain-free intervals for patients who underwent SRS at 1, 2, 3, and more than 3 years after trigeminal neuralgia diagnosis were 68, 37, 36, and 10 months, respectively. Patients who responded to SRS within the first 3 weeks after SRS had a longer duration of complete pain relief compared to those with longer response times (p = 0.001). Fifteen patients (12%) reported new sensory dysfunction after SRS. Conclusion: Early SRS as the initial surgical procedure for management of refractory trigeminal neuralgia was associated with faster, better, and longer pain relief when compared to late SRS. Classification of evidence: This study provides Class IV evidence that in patients with medically refractory trigeminal neuralgia, early stereotactic radiosurgery as the initial procedure provides faster, better, and longer pain relief.

Spinal and Nucleus Caudalis Dorsal Root Entry Zone Lesioning for Chronic Pain: Efficacy and Outcomes

BACKGROUND The role for nucleus caudalis (NC) and spinal dorsal root entry zone (DREZ) lesioning in the management of chronic pain emanating from increased electrical activity in the dorsal horn of the spinal cord and brainstem remains largely uncharted. METHODS All patients who underwent NC and spinal DREZ lesioning by a single surgeon were identified and follow-up was obtained by telephone questionnaires. Patient demographics, surgical details, outcomes, and complications were critically reviewed for all patients identified. RESULTS Of 83 patients identified, 53 (63.9%) were male. Indications for NC DREZ lesioning included trigeminal neuropathic pain (6), trigeminal deafferentation pain (3), glossopharyngeal or occipital neuralgia (3), post-herpetic neuralgia (3), and trauma (1); for spinal DREZ lesioning, indications included brachial plexus avulsion (20), post-herpetic neuralgia (19), spinal cord injury (11), phantom limb pain (8), pelvic pain (5), and complex regional pain syndrome (4). Pain relief was most significant among patients with trigeminal pain, traumatic brachial plexus avulsion injuries, spinal cord injury, and traumatic phantom limb pain. Mean pain reduction averaged 58.3% at a mean follow-up of 8.3 years. Complications included 3 cases of paresis, 3 cases of neuropathy/radiculopathy, 2 cases of ataxia, 3 general medical conditions (colitis, 2; atelectasis, 1), and 2 cases of persistent incisional site pain. Pain relief lasted an average of 4.3 years. CONCLUSIONS Spinal and NC DREZ lesioning can provide effective relief in well-selected patients with intractable chronic pain conditions arising from trigeminal pain, spinal cord injury, brachial plexus avulsions, post-herpetic neuralgia, and phantom limb pain.

Endoscopic endonasal approach for nonvestibular schwannomas.

BACKGROUND Nonvestibular schwannomas of the skull base often represent a challenge owing to their anatomic location. With improved techniques in endoscopic endonasal skull base surgery, resection of various ventral skull base tumors, including schwannomas, has become possible. OBJECTIVE To assess the outcomes of using endoscopic endonasal approach (EEA) for nonvestibular schwannomas of the skull base. METHODS Seventeen patients operated on for skull base schwannomas by EEA at the University of Pittsburgh Medical Center from 2003 to 2009 were reviewed. RESULTS Three patients underwent combined approaches with retromastoid craniectomy (n = 2) and orbitopterional craniotomy (n = 1). Three patients underwent multistage EEA. The rest received a single EEA operation. Data on degree of resection were found for 15 patients. Gross total resection (n = 9) and near-total (>90%) resection (n = 3) were achieved in 12 patients (80%). There were no tumor recurrences or postoperative cerebrospinal fluid leaks. In 3 of 7 patients with preoperative sensory deficits of trigeminal nerve distribution, there were partial improvements. Patients with preoperative reduced vision (n = 1) and cranial nerve VI or III palsies (n = 3) also showed improvement. Five patients had new postoperative trigeminal nerve deficits: 2 had sensory deficits only, 1 had motor deficit only, and 2 had both motor and sensory deficits. Three of these patients had partial improvement, but 3 developed corneal neurotrophic keratopathy. CONCLUSION An EEA provides adequate access for nonvestibular schwannomas invading the skull base, allowing a high degree of resection with a low rate of complications. ABBREVIATIONS CN: cranial nerve EEA: endoscopic endonasal approach ICA: internal carotid artery RMC: retromastoid craniectomy

Calcium Phosphate Cement Cranioplasty Decreases the Rate of Cerebrospinal Fluid Leak and Wound Infection Compared with Titanium Mesh Cranioplasty: Retrospective Study of 672 Patients

OBJECTIVE A variety of biomaterials have been developed for cranial reconstruction after craniectomy, including polyethylene titanium mesh and calcium phosphate cement. This study sought to compare complication rates of calcium phosphate cement and titanium mesh cranioplasty in patients undergoing retromastoid craniectomy. METHODS The authors retrospectively reviewed clinical data from 672 consecutive patients who underwent retromastoid craniectomy at a single institution for microvascular decompression or tumor resection from July 2009 to July 2014. Of these, 336 patients received calcium phosphate cement cranioplasty and 336 underwent (polyethylene) mesh cranioplasty. Charts were abstracted for occurrence of cerebrospinal fluid (CSF) leak, wound infection and/or other wound complication, and the groups were compared. RESULTS In the mesh cranioplasty group, there were 38 complications related to the surgical site, including 18 infections (5.4%), 20 patients (6%) with CSF leak or pseudomeningocele, and no (0%) other wound complications. In the cement cranioplasty cohort, 2 patients (0.6%) experienced wound infection, no patients (0%) had CSF leak, and 2 patients (0.6%) had other wound complications (including one sterile wound dehiscence and one reoperation for removal of excess cement). There was a statistically significant decrease in the rate of wound infection and CSF leak in the patients who underwent cement cranioplasty (P <0.001 for both). CONCLUSIONS Calcium phosphate cement cranioplasty offers an alternative to titanium cranioplasty and may reduce the risk of surgical site complication. Randomized, prospective comparisons of cement cranioplasty to traditional techniques are warranted.

The Dynamic Gait Index in Evaluating Patients with Normal Pressure Hydrocephalus for Cerebrospinal Fluid Diversion

BACKGROUND Diagnosing normal pressure hydrocephalus (NPH) remains challenging. Most clinical tests currently used to evaluate suspected NPH patients for shunt surgery are invasive, require inpatient admission, and are not without complications. An objective, noninvasive, and low-cost alternative would be ideal. METHODS A retrospective review was performed of prospectively collected dynamic gait index (DGI) scores, obtained at baseline and on every day of a 3- to 5-day lumbar cerebrospinal fluid (CSF) drainage trial on patients with suspected NPH at our institution. RESULTS Between 2003 and 2014, 170 patients were suspected to have primary NPH (166, 97.6%) or secondary NPH (4, 2.4%). Using responsiveness to lumbar CSF drainage and subsequent shunting as the reference standard, we found that a baseline DGI ≥ 7 was found to have significant ability in selecting patients for permanent CSF diverting shunt surgery: sensitivity of 84.2% (95% confidence interval [95% CI]: 75.6%-90.2%), specificity of 80.6% (95% CI 70.0%-88.0%), and diagnostic odds ratio of 22.1 (95% CI 9.9-49.3). CONCLUSIONS A baseline DGI ≥ 7 appears to provide an objective, low-cost, noninvasive measure to select patients with suspected NPH for a positive response to CSF diversion with high sensitivity, specificity and diagnostic odds ratio.