Graded decisions in the human brain.

Decision-makers objectively commit to a definitive choice, yet at the subjective level, human decisions appear to be associated with a degree of uncertainty. Whether decisions are definitive (i.e., concluding in all-or-none choices), or whether the underlying representations are graded, remains unclear. To answer this question, we recorded intracranial neural signals directly from the brain while human subjects made perceptual decisions. The recordings revealed that broadband gamma activity reflecting each individual's decision-making process, ramped up gradually while being graded by the accumulated decision evidence. Crucially, this grading effect persisted throughout the decision process without ever reaching a definite bound at the time of choice. This effect was most prominent in the parietal cortex, a brain region traditionally implicated in decision-making. These results provide neural evidence for a graded decision process in humans and an analog framework for flexible choice behavior.

Cerebrospinal Fluid Leakage from Scrotum Secondary to Ventriculoperitoneal Shunt Migration.

Ventriculoperitoneal (VP) shunts are a common neurosurgical procedure used to treat hydrocephalus. Despite their efficacy, many shunts fail and require revisions. The most common causes of shunt failure include obstruction, infection, migration, and perforation. Extraperitoneal migrations require urgent attention. We present a case of migration to the scrotum, a unique complication that may be present in young patients due to the presence of a patent processus vaginalis. Here, we discuss a case of a 16-month-old male patient with a VP shunt presenting with cerebrospinal fluid (CSF) drainage from his scrotum after an indirect hernia repair. This case represents an important reminder for physicians about the sequelae associated with VP shunt complications, particularly extraperitoneal migration, and brings awareness to the underlying factors that may increase this risk.

Drainage, Irrigation, and Fibrinolytic Therapy (DRIFT) for Adult Intraventricular Hemorrhage Associated with Primary Hypertensive Hemorrhages Using IRRAflow Self-Irrigating Catheter: A Report of Three Cases and Prior Historical Controls.

BACKGROUND: Spontaneous primary intracerebral hemorrhage (ICH) accounts for 10%-15% of strokes and is accompanied by ventricular involvement in 10%-30% of cases. Intraventricular hemorrhage (IVH) is a poor prognostic factor and the current treatment paradigm of external ventricular drainage requires frequent flushing and replacement. Given the documented high rate of failure standard EVD catheters, we sought to determine if the use of the IRRAflow system with the addition of alteplase would be beneficial in this patient population for the treatment of IVH associated with primary hypertensive ganglionic hemorrhages. METHODS: Three patients with ganglionic hemorrhages and IVH underwent treatment with the IRRAflow system at our institution from December 2022 to January 2023. A retrospective review was then performed of patients with primary hypertensive ganglionic hemorrhages and EVD placement at our institution from January 2021 to present day. RESULTS: Three patients underwent treatment with the IRRAflow system and continuous lavage of Tissue Plasminogen Activator (tPA). The IVH was efficiently cleared in all cases and the drains were removed within 8 days in all cases. No patients required replacement of the drain and there were no hemorrhagic complications noted. In our retrospective review, 28 patients were identified who underwent placement of a standard EVD for the treatment of primary hypertensive ganglionic hemorrhages. When patients who had early withdrawal of care were excluded, the average length of EVD treatment was 11.3 days and the EVD replacement rate was 24%. CONCLUSIONS: We demonstrate here that the use of the IRRAflow system for the treatment of primary hypertensive hemorrhages with IVH results in rapid clearance of the IVH without safety concerns. Compared to historical controls there was a decrease in EVD duration, EVD replacement and, ICU LOS.

Passive functional mapping of receptive language cortex during general anesthesia using electrocorticography.

OBJECTIVE: To investigate the feasibility of passive functional mapping in the receptive language cortex during general anesthesia using electrocorticographic (ECoG) signals. METHODS: We used subdurally placed ECoG grids to record cortical responses to speech stimuli during awake and anesthesia conditions. We identified the cortical areas with significant responses to the stimuli using the spectro-temporal consistency of the brain signal in the broadband gamma (BBG) frequency band (70-170 Hz). RESULTS: We found that ECoG BBG responses during general anesthesia effectively identify cortical regions associated with receptive language function. Our analyses demonstrated that the ability to identify receptive language cortex varies across different states and depths of anesthesia. We confirmed these results by comparing them to receptive language areas identified during the awake condition. Quantification of these results demonstrated an average sensitivity and specificity of passive language mapping during general anesthesia to be 49±7.7% and 100%, respectively. CONCLUSION: Our results demonstrate that mapping receptive language cortex in patients during general anesthesia is feasible. SIGNIFICANCE: Our proposed protocol could greatly expand the population of patients that can benefit from passive language mapping techniques, and could eliminate the risks associated with electrocortical stimulation during an awake craniotomy.

Rapidly progressive diffuse leptomeningeal glioneuronal tumor in an adult female: illustrative case.

BACKGROUND: Diffuse leptomeningeal glioneuronal tumor (DLGNT) is a rare brain tumor only recently classified by the World Health Organization in 2016 and has few reports on its incidence in adults. OBSERVATIONS: The authors describe a case of DLGNT presenting in a 47-year-old female with seizures, cranial neuropathies, and communicating hydrocephalus with rapid clinical progression. Workup demonstrated progressive leptomeningeal enhancement of the skull base, cranial nerves, and spine, and communicating hydrocephalus. Elevated serum rheumatological markers and early response to systemic corticosteroids and immunosuppressant therapy complicated the diagnosis. Multiple biopsy attempts were required to obtain diagnostic tissue. Pathology demonstrated hypercellularity surrounding leptomeningeal vessels with nuclear atypia, staining positive for GFAP, Olig2, S100, and synaptophysin. Molecular pathology demonstrated loss of chromosome 1p, BRAF overexpression but no rearrangement, and H3K27 mutation. Repeat cerebrospinal fluid (CSF) diversion procedures were required for hydrocephalus management due to high CSF protein content. LESSONS: This report describes a rare, aggressive, adult presentation of DLGNT. Leptomeningeal enhancement and communicating hydrocephalus should raise suspicion for this disease process. Biopsy at early stages of disease progression is essential for early diagnosis and prompt treatment. Further study into the variable clinical presentation, histological and molecular pathology, and optimal means of diagnosis and management is needed.

Risk of Neurological Decline in Patients With Temporal Lobe Brain Masses.

AIM: The objective of this study was to assess which clinical and radiographic findings may be associated with neurological decline in patients with temporal lobe mass lesions. PATIENTS AND METHODS: This represents a retrospective cohort study. Neurological decline was defined as a decline in Glasgow Coma Scale of 2 or more or new anisocoria. Adult patients aged 18 to 89 years with isolated temporal lobe, intra-axial, contrast-enhancing masses diagnosed between 1/1/2010 and 12/31/2020 were included. Clinical and radiographic findings were collected for each patient. Linear regression analysis was used to identify findings predictive of neurological decline. Patients with neurological decline were compared to stable patients to identify factors that may increase risk for neurological decline. RESULTS: A total of 71 patients met the inclusion criteria. Four out of the 71 patients experienced neurological decline, representing an incidence of 6%. Linear regression analysis identified only radiographic transtentorial herniation as a predictor of neurological decline (ß=0.26, p=0.03). A midline shift greater than 5 mm (100% vs. 40%; odds ratio=1.12, 95% confidence interval=1.00-1.32; p=0.05) and radiographic transtentorial herniation (75% vs. 18%; odds ratio=32.12, 95% confidence interval=3.91-264.18; p=0.03) were significantly more prevalent in patients with neurological decline and were associated with an increased risk of neurological decline. CONCLUSION: Radiographic transtentorial herniation and a midline shift greater than 5 mm may be useful findings to suggest an increased risk of neurological decline in patients with masses of the temporal lobe. This knowledge may be useful to neurosurgeons and physicians in other specialties to best care for this patient population.

Comparison of sodium fluorescein and intraoperative ultrasonography in brain tumor resection.

Various intraoperative neuroimaging modalities are available to the neurosurgeon during brain tumor surgery. There remains no consensus on which modalities are superior. This retrospective, single-center cohort study directly compares sodium fluorescein (SF) and intraoperative ultrasonography (IOUS) as intraoperative imaging modalities in a sample of patients with glioblastoma isocitrate dehydrogenase 1 wildtype (GBM). Adult patients with GBM who underwent surgical resection using SF or IOUS guidance between 2010 and 2020 were included. Primary outcomes included extent of resection (EOR), post-operative residual tumor volume, gross total resection (GTR) rate, false negative assessments, and the incidence of new post-operative neurologic deficits. Additionally, pre-and post-test probabilities were calculated to assess each modality's ability to identify residual tumor. 98 patients met inclusion criteria (34 SF and 64 IOUS). Mean EOR was significantly higher for SF (94 ± 11 %) when compared to IOUS (87 ± 20 %; p = 0.032). Mean post-operative residual tumor was significantly higher for IOUS (197 ± 358 mm2) when compared to SF (81 ± 161mm2; p = 0.038). GTR was more frequent with SF (62 % vs 46 %, p = 0.12). False negative assessments for residual tumor were more common with IOUS (22 % vs 15 %, p = 0.53). One patient in each group suffered a new neurologic deficit post-operatively (p = 0.58). Sensitivity, specificity, positive predictive value, and negative predictive value were 62 %, 100 %, 100 %, and 81 % for SF and 59 %, 100 %, 100 %, and 67 % for IOUS, respectively. Taken together, SF may be superior to IOUS in maximizing EOR in patients with GBM, however, both modalities appear to have good efficacy.

Endoscopic Strip Craniectomy and Helmet Therapy for Sagittal Craniosynostosis: An Analysis of Cranial Growth Changes in the Early Postoperative Period.

OBJECTIVE: The purpose of this study is to analyze cranial width and length growth curves in the early postoperative period of patients by undergoing endoscopic sagittal strip craniectomy (ESC) to determine the timing of the maximal growth curve change. By analyzing the complex interplay of cephalic length and width measurements, we hope to better understand the cephalic index (CI) growth curve during this early period. This is the first of a multistep process to elucidate the ideal cranial remolding orthosis (CRO) treatment duration. DESIGN: Retrospective review. SETTING: Tertiary academic institution. PATIENTS: Children with isolated sagittal craniosynostosis. INTERVENTIONS: ESC and postoperative CRO treatment (2015-2019). MAIN OUTCOME MEASURES: One cranial orthotist obtained preoperative and postoperative measurements. The maximal rate of change of width, length, and CI were compared against the postoperative week these occurred. RESULTS: Thirteen children (mean age: 3.3 months, average preoperative CI: 73.4) underwent this intervention. CI reached its highest growth rate by 4.9 average weeks postoperatively, which correlated with the maximal width growth rate (5.2 weeks). Length curves reached their maximal growth rate by 15.5 weeks. CI peaked (81.3) by 22.7 weeks postoperatively, a significant increase from baseline. CONCLUSIONS: Following ESC, in the early postoperative period, the CI growth curve has 4 phases: initial rapid expansion, early and late slowed expansion, and plateau, followed by possible regression phases. This highlights the importance of early postoperative CRO initiation, CRO compliance, and properly fitting CROs, especially in the first 2 phases. This data sets the stage for investigating the ideal treatment length.

Does Pre-existing Anticoagulation or Antiplatelet Therapy Increase the Risk of Traumatic Subarachnoid Hemorrhage Progression?

BACKGROUND: Isolated traumatic subarachnoid hemorrhage (tSAH) is a common finding in mild traumatic brain injury that often results in transfer to a tertiary center. Patients prescribed blood-thinning medications (BTs) are believed to be at higher risk of clinical or radiographic worsening. OBJECTIVE: To compare the rates of radiographic progression and need for neurosurgical intervention in patients with tSAH who are on anticoagulation (AC) and antiplatelet (AP) therapies with those who are not. METHODS: Analysis using a retrospective cohort design identified patients older than 18 years with isolated tSAH and a Glasgow Coma Scale of 15 on admission. Clinical information including use of BTs, administration of reversal agents, radiographic progression, and need for neurosurgical intervention was collected. Patients on BTs were divided into AP, AC, and AP/AC groups based on drug type. RESULTS: Three hundred eighty-four patients were included with 203 in the non-BT group and 181 in the BT group. Overall, 2.1% had worsening scans, and none required operative intervention. There was no difference in radiographic worsening between the non-BT and BT groups (2.4% vs 1.6%; P = 1.00). Crosswise comparison revealed no difference between the non-BT group and each BT subtype (AP, AP/AC, or AC). The non-BT group was more likely to have radiographic improvement than the BT group (45.8% vs 30.9%; P = .002). CONCLUSION: Neurologically intact patients on BTs with isolated tSAH are not at increased risk of radiographic progression or neurosurgical intervention. The presence of BTs should not influence management decisions for increased surveillance.

Utility of 3-dimensionally printed models for parent education in pediatric plagiocephaly.

Objectives: Demonstrate the benefits of using 3D printed skull models when counseling families regarding disorders of the cranial vault (namely plagiocephaly and craniosynostosis), as traditional imaging review and discussion is often insufficient. Methods: 3D printed skull models of a patient with plagiocephaly were used during clinic appointments to aid in the counseling of parents. Surveys were distributed following the appointment to evaluate the utility of these models during the discussion. Results: Fifty surveys were distributed (with a 98% response rate). 3D models were both empirically and anecdotally helpful for parents in understanding their child's diagnosis. Conclusion: Advances in 3D printing technology and software have made producing models more accessible. Incorporating physical, disorder-specific models into our discussions has led to improvements in our ability to communicate with our patients and their families. Innovation: Disorders of the cranial can be challenging to describe to the parents and guardians of affected children; using 3D printed models is a useful adjunct in patient-centered discussions. The subject response to the use of these emerging technologies in this setting suggests a major role for 3D models in patient education and counseling for cranial vault disorders.

Growth hormone replacement therapy: is it safe to use in children with asymptomatic pituitary lesions?

OBJECTIVES: Small pituitary cysts are commonly discovered on pediatric brain magnetic resonance imagings (MRIs), particularly in patients with growth hormone deficiency (GHD). We examined the need for operative management in children with these masses as well as the effect of growth hormone replacement (GHR) on these lesions. METHODS: This was a retrospective review of pituitary protocol MRIs conducted in children 0-19 at a single center between April 2010-November 2020. Sex, indication for initial MRI, volume, and whether surgery was performed was determined. Records were reviewed to determine whether GHD was present and treatment with GHR documented. For patients with subsequent MRIs, volume on most recent scan was calculated. RESULTS: Of the 101 children with cysts, 25 had laboratory-confirmed GHD and 76 did not. GHD patients had a higher mean age compared to no growth hormone deficiency (NGHD) cohort (11.2 and 8.4 years, respectively; p=0.02) and a larger proportion of males (p<0.001). The mean cyst volume on initial MRI was not significantly smaller in patients with GHD (0.063 ± 0.012 cm3) vs. those without GHD (0.171 ± 0.039 cm3, p=0.11). Of the 21 GHD patients who received GHR and had follow-up MRIs, 10 had no change in pituitary cyst size, two had cysts that shrank, and seven disappeared. The remaining two cysts enlarged an average of 0.061 ± 0.033 cm3. Zero GHR recipients required surgical intervention. CONCLUSIONS: Small sellar cysts discovered incidentally on imaging in children are unlikely to require surgical intervention. GHR does not appear to significantly enlarge these pediatric pituitary lesions and is safe for use.

Shuntogram utility in predicting future shunt failures.

OBJECTIVE: Shunt failure remains a challenging diagnosis for neurosurgeons, particularly when patient symptoms suggest shunt malfunction but radiographic evidence is lacking. In such situations, shuntograms are sometimes employed to guide medical decision-making. In this study, the authors aimed to investigate the utility of shuntograms in aiding patient management, particularly in terms of a negative result. METHODS: This retrospective single-institution series comprises patients who underwent a shuntogram procedure to evaluate shunt patency over a roughly 6-year period. The medical records of patients were reviewed to determine the findings of the shuntogram procedure, the type of obstruction, and whether a subsequent operation for a shunt revision took place either within 30 days or up to 1 year after the procedure. Statistical analysis was completed by calculating the sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) of the shuntogram as compared with the revision surgery. RESULTS: Of the 98 patients who underwent a shuntogram, 95 patients were included in the statistical analysis. A ventriculoperitoneal shunt was assessed in 81% of patients (77/95). The PPV of the procedure was 100%. The NPV for predicting a subsequent shunt revision within 30 days was 68.3% (false-negative rate of 31.7%) or within 365 days was 61.2% (false-negative rate of 38.8%). The sensitivity and specificity of the shuntogram were 55.8% and 100% within 30 days and 51.9% and 100% within 365 days, respectively. The most common intervention at the time of surgery following a negative shuntogram was a valve replacement in 38.5% of patients (10/26). CONCLUSIONS: With an NPV of 68.3% for predicting revision within 30 days in our series of 95 patients, shuntograms remained a useful tool in the clinical decision-making process when evaluating potential shunt failure.

An Effective, Reproducible, and Cost-Effective Approach for Achieving Symmetry in Bicoronal Incisions in Pediatric Patients Undergoing Craniofacial Surgery.

SUMMARY: Bicoronal incisions are frequently used for exposure and access to the craniofacial skeleton. A zigzag design is often used to camouflage the resultant scar. Often, free-hand zigzag drawings require several correction attempts to ensure symmetry because of the need for replication of multiple limbs of the bicoronal incision that need to be similar lengths, distance, and angles from each other. The authors present a novel technique using a template that rapidly and consistently achieves symmetric zigzag bicoronal incisions. The device is a hairstyling device that is inherently geometric in its design. Retrospective results of pediatric craniofacial patients from 2010 to 2018 are presented. Patients undergoing endoscopic reconstructions and patients who had prior operations at other institutions were excluded from the study. Fifty-two patients met inclusion criteria, with age at surgery ranging from 3 to 207 months (mean, 17 months). Follow-up ranged from 1 to 66 months (mean, 26 months). Data collected included demographics, type of surgery, and operative outcomes, including incision-related complications. Using this dynamic hairstyling device in a novel application as a template results in a fast, effective, and easily reproducible symmetric bicoronal zigzag incision in all cases. This technique eliminates the need for adjusting the length and angles of bicoronal incisions, and it can be adapted across a variety of head sizes and shapes in both pediatric and adult populations.

Optic Nerve Gliomas.

Objectives To describe the diagnostic and management features of optic nerve gliomas. Design Literature review. Results Optic nerve gliomas are generally benign in the pediatric age group although they are usually malignant and aggressive in adults. As such, the mechanisms by which these lesions are diagnosed, the systemic implications, the goals of intervention, and the nature of therapeutic management all differ between these tumors. Conclusions This article addresses these lesions and discusses the diagnostic and therapeutic paradigms by which they may be approached.

Does One Week of Postoperative Antibiotic Prophylaxis Reduce the Rate of Infection After Vagus Nerve Stimulator Surgery?

OBJECTIVE: Vagus nerve stimulation (VNS) therapy is an increasingly popular treatment for medically intractable epilepsy. During a review of our cases, we noted that one of the senior authors give patients 1 week of antibiotic prophylaxis after VNS surgery while the other does not. We reviewed our experience with postoperative antibiotic prophylaxis after VNS surgery. METHODS: We retrospectively reviewed the records of patients from January 2009 to September 2018 who had undergone surgery for VNS therapy, including generator replacement. The office and operative notes were reviewed to obtain the indications and operative details for VNS placement. RESULTS: A total of 570 operations were reviewed, 232 of which were primary implantations and 338 were revisions. The indication was intractable epilepsy in all cases. A total of 5 infections occurred, 4 in the group with postoperative antibiotic prophylaxis and 1 in the group without. The difference was not statistically significant. CONCLUSION: Just as with any hardware implantation, infection of the hardware can lead to significant morbidity. However, the use of postoperative oral antibiotic prophylaxis did not show benefit in reducing the infection rate.

Deficiency of Microglial Autophagy Increases the Density of Oligodendrocytes and Susceptibility to Severe Forms of Seizures.

Excessive activation of mTOR in microglia impairs CNS homeostasis and causes severe epilepsy. Autophagy constitutes an important part of mTOR signaling. The contribution of microglial autophagy to CNS homeostasis and epilepsy remains to be determined. Here, we report that ATG7KO mice deficient for autophagy in microglia display a marked increase of myelination markers, a higher density of mature oligodendrocytes (ODCs), and altered lengths of the nodes of Ranvier. Moreover, we found that deficiency of microglial autophagy (ATG7KO) leads to increased seizure susceptibility in three seizure models (pilocarpine, kainic acid, and amygdala kindling). We demonstrated that ATG7KO mice develop severe generalized seizures and display nearly 100% mortality to convulsions induced by pilocarpine and kainic acid. In the amygdala kindling model, we observed significant facilitation of contralateral propagation of seizures, a process underlying the development of generalized seizures. Taken together, our results reveal impaired microglial autophagy as a novel mechanism underlying altered homeostasis of ODCs and increased susceptibility to severe and fatal generalized seizures.

High lead impedances requiring revision during vagal nerve stimulator generator replacement.

OBJECTIVE: Vagal nerve stimulation (VNS) therapy is among the growing options in the treatment of intractable epilepsy. The phenomenon of surprise lead impedance issues found at the time of surgery resulting in unplanned lead revision is a challenge with this type of device. We reviewed our experience with VNS revisions. MATERIAL AND METHODS: We retrospectively reviewed the records of all adult and pediatric patients between January 2009 and September 2018 who underwent surgery for VNS therapy, including revision surgery. Office and operative notes were reviewed to obtain the indications and operative details for VNS placement. RESULTS: A total of 570 operations were reviewed. The indication was intractable epilepsy in all cases. Primary implantation was performed in 232 patients, while the remaining 338 cases were revision cases of various natures. Surprise high lead impedance was found in 10 (3%) of these cases, resulting in a significantly increased complexity of surgery in those instances. CONCLUSION: Lead impedance issues can be caused by disconnection, electrode fracture, hardware failure, or tissue scarring but ultimately require a more extended surgery than may be initially planned. Anticipating the potential for a more extensive operation than a simple generator replacement may prevent perioperative frustrations on both sides.

Pediatric cervical spine injury in the United States: Defining the burden of injury, need for operative intervention, and disparities in imaging across trauma centers.

BACKGROUND: Pediatric cervical spine injury (PCSI) in children is rare. Incidence of PCSI requiring intervention is not known, and imaging practices for screening in United States trauma centers are not well described. METHODS: The 2016 NTDB was queried for patients younger than 15 years with PCSI. Incidence of PCSI, operative interventions, and imaging rates were analyzed by age and ACS accreditation status. RESULTS: Of 84,554 children, 873 (1.03%) had PCSI. Patients <4 years were less likely to have PCSI (0.68% vs. 1.1%, RR 0.59, p < 0.001). 165 children (0.20%) required an intervention for PCSI. 12.8% of all children were screened for PCSI with imaging, 9.3% with CT, and 3.2% with plain X-rays. In spite of similar injury and intervention rates, stand-alone pediatric trauma centers were less likely than others to image patients without PCSI (11% vs. 13% p < 0.001), less likely to utilize CT scan (5.8% vs. 10.6% p < 0.001) and more likely to utilize plain films (5.2% vs. 2.4% p < 0.001). CONCLUSION: Despite exceedingly low rates of PSCI requiring intervention (0.2%), imaging rates for screening are significant. Stand-alone pediatric trauma centers outperform others in limiting unnecessary imaging. LEVEL OF EVIDENCE: IV.

Analysis of shunted hydrocephalus follow-up: What do routine clinic visits yield? What factors affect revision surgery presentation and outcomes?

Frequency and duration of outpatient clinic follow-up for patients with shunted hydrocephalus varies among clinicians and assessment of follow-up regimens is lacking. The aim of this study is to investigate whether routine clinic visits alter care and whether they identify patients requiring shunt revision surgery, as well as, to better understand how patients utilize the outpatient clinic and present for shunt revision evaluation. This is a single-centered retrospective study of 154 patients requiring shunt revision surgery from 2009 to 2018 who had at least one prior clinic evaluation. The median age for shunt placement and revision were 3 months and 11 years old, respectively. Routine clinic visits led to a change in care for 16 patients (10.4%); including additional imaging, follow-up, or a combination of the two. With regards to revision surgery, days from prior shunt surgery, Chiari II/myelomeningocele pathology, and shunt type (p < 0.01) did affect time to presentation. Four patients (2.6%) requiring revision surgery were identified at routine clinic follow-up, while 92 (59.7%) and 47 (30.5%) presented to the emergency department and clinic sick visit, respectively. Presentation to clinic resulted in a statistically significant decrease in shunt revision surgery length-of-stay compared to presentation to the emergency department or inpatient admission for another condition. Even with increased emergency room utilization, increased clinic connectivity, and improved patient education, routine clinic visits remain an important component in the follow-up of patients with shunted hydrocephalus by helping to guide clinical care and identify patients requiring shunt revision surgery.