Jason Liauw

Techniques and accuracy of thoracolumbar pedicle screw placement

Pedicle screw instrumentation has been used to stabilize the thoracolumbar spine for several decades. Although pedicle screws were originally placed via a free-hand technique, there has been a movement in favor of pedicle screw placement with the aid of imaging. Such assistive techniques include fluoroscopy guidance and stereotactic navigation. Imaging has the benefit of increased visualization of a pedicles trajectory, but can result in increased morbidity associated with radiation exposure, increased time expenditure, and possible workflow interruption. Many institutions have reported high accuracies with each of these three core techniques. However, due to differing definitions of accuracy and varying radiographic analyses, it is extremely difficult to compare studies side-by-side to determine which techniques are superior. From the literature, it can be concluded that pedicles of vertebrae within the mid-thoracic spine and vertebrae that have altered morphology due to scoliosis or other deformities are the most difficult to cannulate. Thus, spine surgeons would benefit the most from using assistive technologies in these circumstances. All other pedicles in the thoracolumbar spine should theoretically be cannulated with ease via a free-hand technique, given appropriate training and experience. Despite these global recommendations, appropriate techniques must be chosen at the surgeons discretion. Such determinations should be based on the surgeons experience and the specific pathology that will be treated.

Multidisciplinary approach for improved outcomes in secondary cranial reconstruction: introducing the pericranial-onlay cranioplasty technique.

BACKGROUND: Although materials for secondary cranial reconstruction have evolved with time, the overall approach in terms of bone flap/implant reconstruction after necessary delay has remained constant. OBJECTIVE: To present our cases series of 50 consecutive secondary cranial reconstruction patients and to describe a multidisciplinary cranioplasty approach developed to reduce morbidity, to minimize infection, and to improve aesthetic appearance. METHODS: Standard technique teaches us to place the bone flap and/or alloplastic implant directly over the dura or dural protectant after scalp flap re-elevation. However, this procedure is fraught with high complication rates, including infection. While raising the previously incised scalp flap overlying the full-thickness calvarial defect, the dissection is performed within the loose areolar tissue plane beneath the galea aponeurosis, thus leaving vascularized pericranium intact over the dura. RESULTS: A total of 50 consecutive patients were treated by the senior author encompassing 46 cranioplasties using the pericranial-onlay approach, along with 4 isolated temporal soft tissue reconstructions with liquid poly-methyl-methacrylate. Of the 46 cranioplasties (> 5 cm2), only 1 autologous bone flap developed deep infection necessitating bone flap removal (1 of 46, 2.17%; 95% confidence interval, 0.003-11.3). None of the alloplastic custom implants placed have developed any infection requiring removal. CONCLUSION: This multidisciplinary approach illustrated in our case series, including our “pericranial-onlay” technique described here for the first time, has the potential to improve patient outcomes, to decrease perioperative morbidity, and to minimize costs associated with postoperative infections after secondary cranial reconstruction. ABBREVIATIONS: CCI, custom cranial implant PMMA, poly-methyl-methacrylate

Automatic Localization of Target Vertebrae in Spine Surgery: Clinical Evaluation of the LevelCheck Registration Algorithm

Study Design. A 3-dimensional-2-dimensional (3D-2D) image registration algorithm, “LevelCheck,” was used to automatically label vertebrae in intraoperative mobile radiographs obtained during spine surgery. Accuracy, computation time, and potential failure modes were evaluated in a retrospective study of 20 patients. Objective. To measure the performance of the LevelCheck algorithm using clinical images acquired during spine surgery. Summary of Background Data. In spine surgery, the potential for wrong level surgery is significant due to the difficulty of localizing target vertebrae based solely on visual impression, palpation, and fluoroscopy. To remedy this difficulty and reduce the risk of wrong-level surgery, our team introduced a program (dubbed LevelCheck) to automatically localize target vertebrae in mobile radiographs using robust 3D-2D image registration to preoperative computed tomographic (CT) scan. Methods. Twenty consecutive patients undergoing thoracolumbar spine surgery, for whom both a preoperative CT scan and an intraoperative mobile radiograph were available, were retrospectively analyzed. A board-certified neuroradiologist determined the “true” vertebra levels in each radiograph. Registration of the preoperative CT scan to the intraoperative radiograph was calculated via LevelCheck, and projection distance errors were analyzed. Five hundred random initializations were performed for each patient, and algorithm settings (viz, the number of robust multistarts, ranging 50–200) were varied to evaluate the trade-off between registration error and computation time. Failure mode analysis was performed by individually analyzing unsuccessful registrations (>5 mm distance error) observed with 50 multistarts. Results. At 200 robust multistarts (computation time of ∼26 s), the registration accuracy was 100% across all 10,000 trials. As the number of multistarts (and computation time) decreased, the registration remained fairly robust, down to 99.3% registration accuracy at 50 multistarts (computation time ∼7 s). Conclusion. The LevelCheck algorithm correctly identified target vertebrae in intraoperative mobile radiographs of the thoracolumbar spine, demonstrating acceptable computation time, compatibility with routinely obtained preoperative CT scans, and warranting investigation in prospective studies. Level of Evidence: N/A

Incidence and clinical significance of vascular encroachment resulting from freehand placement of pedicle screws in the thoracic and lumbar spine: analysis of 6816 consecutive screws.

Study Design. Retrospective case series. Objective. Evaluate the incidence and clinical significance of vascular encroachment resulting from freehand placement of pedicle screws in the thoracic and lumbosacral spine. Summary of Background Data. Pedicle screws are routinely used to effectively stabilize all 3 columns of the spine but can be technically demanding to place in the setting of variable anatomy. There is a paucity of data regarding iatrogenic major vascular injuries during posterior instrumentation procedures. Methods. We retrospectively reviewed the records of all patients undergoing freehand pedicle screw placement without image guidance in the thoracic or lumbar spine during a 7-year period. The incidence and extent of vascular encroachment by a pedicle screw was determined by review of routine postoperative computed tomographic scans obtained within 24 hours of all surgical procedures. Vascular encroachment was defined as a pedicle screw that was touching or deforming the wall of a major vessel. Results. A total of 964 patients received 6816 freehand-placed pedicle screws in the thoracolumbar spine. Fifteen (0.22%) screws that encroached a major vascular structure were identified. Ten (0.29%) thoracic pedicle screws encroached on the aorta, 4 (0.14%) lumbar screws on the common iliac vein, and 1 S1 screw (0.19%) on the internal iliac vein. In consultation with vascular surgery, it was determined whether revision surgery and the technique/approach for the revision procedure should be recommended. Two (0.21%) patients required revision surgery to remove the encroaching pedicle screw (T5 and T8) due to concern for vascular injury. Both patients were asymptomatic and recovered without further complications after revision surgery. Conclusion. Vascular encroachment of major vessels occurs rarely in the setting of freehand pedicle screw placement in the thoracolumbar spine. Although rare, delayed vascular injury from errant pedicle screw placement has been reported in the literature. The aorta seems to be the vessel at the highest risk of injury. Routine intraoperative or postoperative computed tomographic scanning allows for early identification of pedicle screws encroaching on vascular structures thereby facilitating early revision surgery. Level of Evidence: 4

Prognostic factors associated with pain palliation after spine stereotactic body radiation therapy

OBJECT The number of patients with spinal tumors is rapidly increasing; spinal metastases develop in more than 30% of cancer patients during the course of their illness. Such lesions can significantly decrease quality of life, often necessitating treatment. Stereotactic radiosurgery has effectively achieved local control and symptomatic relief for these patients. The authors determined prognostic factors that predicted pain palliation and report overall institutional outcomes after spine stereotactic body radiation therapy (SBRT). METHODS Records of patients who had undergone treatment with SBRT for either primary spinal tumors or spinal metastases from June 2008 through June 2013 were retrospectively reviewed. Data were collected at the initial visit just before treatment and at 1-, 3-, 6-, and 12-month follow-up visits. Collected clinical data included Karnofsky Performance Scale scores, pain status, presence of neurological deficits, and prior radiation exposure at the level of interest. Radiation treatment plan parameters (dose, fractionation, and target coverage) were recorded. To determine the initial extent of epidural spinal cord compression (ESCC), the authors retrospectively reviewed MR images, assessed spinal instability according to the Bilsky scale, and evaluated lesion progression after treatment. RESULTS The study included 99 patients (mean age 60.4 years). The median survival time was 9.1 months (95% CI 6.9-17.2 months). Significant decreases in the proportion of patients reporting pain were observed at 3 months (p < 0.0001), 6 months (p = 0.0002), and 12 months (p = 0.0019) after treatment. Significant decreases in the number of patients reporting pain were also observed at the last follow-up visit (p = 0.00020) (median follow-up time 6.1 months, range 1.0-56.6 months). Univariate analyses revealed that significant predictors of persistent pain after intervention were initial ESCC grade, stratified by a Bilsky grade of 1c (p = 0.0058); initial American Spinal Injury Association grade of D (p = 0.011); initial Karnofsky Performance Scale score, stratified by a score of 80 (p = 0.002); the presence of multiple treated lesions (p = 0.044); and prior radiation at the site of interest (p < 0.0001). However, when multivariate analyses were performed on all variables with p values less than 0.05, the only predictor of pain at last follow-up visit was a prior history of radiation at the site of interest (p = 0.0038), although initial ESCC grade trended toward significance (p = 0.073). Using pain outcomes at 3 months, at this follow-up time point, pain could be predicted by receipt of radiation above a threshold biologically effective dose of 66.7 Gy. CONCLUSIONS Pain palliation occurs as early as 3 months after treatment; significant differences in pain reporting are also observed at 6 and 12 months. Pain palliation is limited for patients with spinal tumors with epidural extension that deforms the cord and for patients who have previously received radiation to the same site. Further investigation into the optimal dose and fractionation schedule are needed, but improved outcomes were observed in patients who received radiation at a biologically effective dose (with an a/b of 3.0) of 66.7 Gy or higher.

Quantitative study of parathyroid hormone (1-34) and bone morphogenetic protein-2 on spinal fusion outcomes in a rabbit model of lumbar dorsolateral intertransverse process arthrodesis

Study Design. A posterolateral rabbit spinal fusion model was used to evaluate the effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) and teriparatide (PTH [1–34]) used individually and in combination on spinal fusion outcomes. Objective. To test the efficacy of parathyroid hormone on improving spinal fusion outcomes when used with BMP-2. Summary of Background Data. Of the more than 250,000 spinal fusion surgical procedures performed each year, 5% to 35% of these will result in pseudarthrosis. Growing controversy on the efficacy and cost of rhBMP-2 for improving spinal fusion outcomes has presented a challenge for clinicians. Research into PTH as an adjunct therapy to rhBMP-2 for spinal fusion has not yet been investigated. Methods. Forty-eight male New Zealand white rabbits underwent bilateral posterolateral intertransverse process arthrodesis surgery at the L5–L6 level. Animals were divided into 6 groups. Two groups were treated with autograft alone or autograft and PTH (1-34), whereas the other 4 groups were treated with low-dose rhBMP-2 alone, high-dose rhBMP-2 alone, or either dose combined with PTH (1-34). All animals were euthanized 6 weeks after surgery. The L4–L7 spinal segment was removed and assessed using manual palpation, computed tomography (CT), and biomechanical testing. Results. CT assessments revealed fusion in 50% of autograft controls, 75% of autograft PTH (1-34) animals, 87.5% in the 2 groups treated with low-dose rhBMP-2, and 100% in the 2 groups treated with high-dose rhBMP-2. CT volumetric analysis demonstrated that all groups treated with biologics had fusion masses that were on average significantly larger than those observed in the control group (P < 0.0001). Biomechanical data demonstrated no statistical difference between controls, PTH (1-34), and low-dose rhBMP-2 in any testing orientation. PTH (1-34) did not increase bending stiffness when used adjunctively with either low-dose or high-dose rhBMP-2. Conclusion. Although intermittent teriparatide administration results in increased fusion mass volume, it does not improve biomechnical stiffness over use of autograft alone. When delivered concurrently with high- and low-dose rhBMP-2, teriparatide provided no statistically significant improvement in biomechanical stiffness. Level of Evidence: N/A

Anticoagulation for Hypercoagulable Patients Associated with Complications after Large Cranioplasty Reconstruction

Background: Despite advancements in materials and techniques used for cranial reconstruction, complication rates following reconstructive cranioplasty remain significant. Methods: In this study, the authors assessed the association of perioperative anticoagulation use and/or a hypercoagulable state with minor (i.e., not requiring surgical intervention) and major (i.e., surgical intervention required) complications after reconstructive cranioplasty for large skull defects. A retrospective cohort review of 108 consecutive cranioplasties performed between 2011 and 2014 was conducted. A multiple logistic regression analysis was performed to identify the adjusted association between the predictor variables and complications. Results: Twenty-three primary (21.3 percent) and 85 secondary (78.7 percent) cranioplasties were performed on 94 patients with a median age of 50 years (interquartile range, 38 to 63 years). Median full-thickness calvarial defect size was 154 cm2 (interquartile range, 104 to 230 cm2). Eleven minor (10.2 percent) and 18 major postoperative complications (16.7 percent) occurred in 26 cases (24.1 percent). Multiple logistic regression analysis revealed that coagulation status (i.e., perioperative use of anticoagulation therapy or hypercoagulable state) was statistically significant in predicting minor complications (OR, 7.8; 95 percent CI, 2.4 to 25.2; p = 0.001). Of note, the odds of a minor complication were an order of magnitude higher when both perioperative anticoagulation and a hypercoagulable state were present. Conclusion: To the authors’ knowledge, this is the first study to document that the use of perioperative anticoagulant therapy for patients with thromboembolic conditions is a positive predictor of complications following cranioplasty reconstruction. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, III.

Far-lateral transcondylar approach for microsurgical trapping of an anterior inferior cerebellar artery aneurysm

Aneurysms of the posterior circulation remain challenging lesions given their proximity to the brainstem and cranial nerves. Many of these aneurysms may best be approached through a retrosigmoid-suboccipital craniectomy with a far-lateral transcondylar extension. In this narrated video illustration, we present the case of a 37-year-old man with an incidentally discovered right-sided anterior inferior cerebellar artery (AICA) aneurysm. Diagnostic studies included CT angiography and cerebral angiography. A suboccipital craniectomy and far-lateral transcondylar extension were performed for microsurgical trapping and excision of the AICA aneurysm. The techniques of the retrosigmoid craniectomy, C-1 laminectomy, condylectomy and microsurgical trapping of the aneurysm are reviewed. The video can be found here: http://youtu.be/JiM3CXVwXnk.

Microsurgical obliteration of a thoracic spinal perimedullary arteriovenous fistula

Spinal vascular lesions are rare and may be classified as a) dural arteriovenous fistulas (AVFs), b) arteriovenous malformations, or c) perimedullary AVFs. In this narrated video illustration, we present the case of a 71-year-old woman who presented with progressive bilateral lower extremity weakness and urinary retention who was diagnosed with a thoracic spinal perimedullary arteriovenous fistula. The diagnostic studies included a thoracic MRI and spinal angiogram. A multilevel thoracic laminoplasty was performed for microsurgical obliteration of the AVF. The techniques of intraoperative angiography, thoracic laminoplasty and microsurgical obliteration and resection of the AVF are reviewed. The video can be found here: http://youtu.be/5vVp3oq5sLg.

Metastatic extrapulmonary small cell carcinoma to the cerebellopontine angle: a case report and review of the literature.

Extrapulmonary small cell carcinomas (EPSCC) are rare malignancies with poor patient prognoses. We present the case of a 63-year-old male who underwent surgical resection of a poorly differentiated small cell carcinoma, likely from a small intestinal primary tumor that metastasized to the cerebellopontine angle (CPA). A 63-year-old male presented with mild left facial paralysis, hearing loss, and balance instability. MRI revealed a 15 mm mass in the left CPA involving the internal auditory canal consistent with a vestibular schwannoma. Preoperative MRI eight weeks later demonstrated marked enlargement to 35 mm. The patient underwent a suboccipital craniectomy and the mass was grossly different visually and in consistency from a standard vestibular schwannoma. The final pathology revealed a poorly differentiated small cell carcinoma. Postoperative PET scan identified avid uptake in the small intestine suggestive of either a small intestinal primary tumor or additional metastatic disease. The patient underwent whole brain radiation therapy and chemotherapy and at last follow-up demonstrated improvement in his symptoms. Surgical resection and radiotherapy are potential treatment options to improve survival in patients diagnosed with NET brain metastases. We present the first documented case of skull base metastasis of a poorly differentiated small cell carcinoma involving the CPA.