Impact of Motor-Evoked Potential Monitoring on Facial Nerve Outcomes after Vestibular Schwannoma Resection

Objectives:

Assess the utility of intraoperative transcranial facial motor-evoked potential (FMEP) monitoring in predicting and improving facial function after vestibular schwannoma (VS) resection.

Study Design:

Retrospective chart review.

Methods:

Data were obtained from 82 consecutive VS resections meeting inclusion criteria. Sixty-two cases were performed without FMEP and 20 with FMEP. Degradation of FMEP response was defined as a final-to-baseline amplitude ratio of 0.5 or less. House-Brackmann (HB) grade was assessed preoperatively, postoperatively, at follow-up assessments, and it was compared between pre- and post-FMEP cohorts. Positive predictive value (PPV) and negative predictive value (NPV), sensitivity, and specificity of FMEP degradation in predicting facial weakness were calculated.

Results:

In the pre-FMEP group, at length of follow-up (LOF) ⩾9 months, 83.9% (52/62) of patients exhibited HB 1-2 outcome. In the post-FMEP cohort, 75.0% (15/20) exhibited HB 1-2 function at LOF ⩾9 months. There was no difference in rates of HB 1-2 outcomes between groups in the immediate postoperative period ( P = .35) or at long-term follow-up ( P = 1.0). With respect to predicting immediate postoperative facial function, FMEP demonstrated high specificity (88.9%) and moderate sensitivity (54.5%). The PPV and NPV for immediate postoperative facial function were 85.7% and 61.5%, respectively. With respect to long-term (⩾9 months LOF) facial function, intraoperative FMEP was moderately sensitive (71.4%) and highly specific (84.6%); PPV was moderate (71.4%), and NPV was high (84.6%).

Conclusions:

Intraoperative FMEP is highly specific and moderately sensitive in predicting postoperative facial function for patients undergoing VS resection, but its use may not be associated with improved facial nerve outcomes.

Level of Evidence:

4

UV light absorption parameters of the pathobiologically implicated bilirubin oxidation products, MVM, BOX A, and BOX B

The formation of the bilirubin oxidation products (BOXes), BOX A ([4-methyl-5-oxo-3-vinyl-(1,5-dihydropyrrol-2-ylidene)acetamide]) and BOX B (3-methyl-5-oxo-4-vinyl-(1,5-dihydropyrrol-2-ylidene)acetamide), as well as MVM (4-methyl-3-vinylmaleimide) were synthesized by oxidation of bilirubin with H₂O₂ without and with FeCl₃, respectively. Compound identity was confirmed with NMR and mass spectrometry (MS; less than 1 ppm, tandem MS up to MS⁴). UV absorption profiles, including λ_max, and extinction coefficient (ε; estimated using NMR) for BOX A, BOX B, and MVM in H₂O, 15% CH₃CN plus 10 mM CF₃CO₂H, CH₃CN, CHCl₃, CH₂Cl₂, and 0.9% NaCl were determined. At longer wavelengths, λ_max's for 1) BOX A were little affected by the solvent, ranging from 295-297 nm; 2) BOX B, less polar solvent yielded λ_max's of lower wavelength, with values ranging from 308-313 nm, and 3) MVM, less polar solvent yielded λ_max's of higher wavelength, with values ranging from 318-327 nm. Estimated ε's for BOX A and BOX B were approximately 5- to 10-fold greater than for MVM.

Middle Fossa Approach for Resection of Vestibular Schwannomas: A Decade of Experience

BACKGROUND

The middle cranial fossa (MCF) approach is a challenging surgical technique for the resection of small and intermediate sized, primarily intracanalicular, vestibular schwannomas (VS), with the goal of hearing preservation (HP).

OBJECTIVE

To describe a decade-long, single institutional experience with the MCF approach for resection of VS.

METHODS

This is a retrospective cohort study of 63 patients who underwent the MCF approach for resection of VS from 2006 to 2016. Audiometric data included pure-tone average (PTA), low-tone pure-tone average (LtPTA), word recognition score, and American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) hearing classification at presentation and follow-up. Patients with postoperative serviceable (AAO-HNS class A-B) and/or useful (AAO-HNS class A-C) hearing were compared to those without HP. Facial nerve function was assessed using the House–Brackmann scale.

RESULTS

The mean age and duration of follow-up were 50 ± 13 yr and 21 ± 21 mo, respectively. The mean tumor size was 10 ± 4 mm. The serviceable and usable HP rates were 54% and 50%, respectively. Some residual hearing was preserved in 71% of patients. Large tumor size (P = .05), volume (P = .03), and extrameatal tumor extension (P = .03) were associated with poor audiometric outcomes. The presence of a fundal fluid cap (P = .01) was a favorable finding. At definitive testing, LtPTA was significantly better preserved than traditional PTA (P = .01). Facial nerve outcomes, tumor control rates, and durability of audiometric outcomes were excellent. 47% of patients pursued aural rehabilitation.

CONCLUSION

In our series, the MCF approach for VS provided excellent rates of tumor and facial nerve function, with durable serviceable HP.

Surgical Performance in Minimally Invasive Surgery Plus Recombinant Tissue Plasminogen Activator for Intracerebral Hemorrhage Evacuation Phase III Clinical Trial

BACKGROUND

Minimally invasive thrombolytic evacuation of intracerebral hematoma is being investigated in the ongoing phase III clinical trial of Minimally Invasive Surgery plus recombinant Tissue plasminogen activator for Intracerebral hemorrhage Evacuation (MISTIE III).

OBJECTIVE

To assess the accuracy of catheter placement and efficacy of hematoma evacuation in relation to surgical approach and surgeon experience.

METHODS

We performed a trial midpoint interim assessment of 123 cases that underwent the surgical procedure. Accuracy of catheter placement was prospectively assessed by the trial Surgical Center based on prearticulated criteria. Hematoma evacuation efficacy was evaluated based on absolute volume reduction, percentage hematoma evacuation, and reaching the target end-of-treatment volume of <15 mL. One of 3 surgical trajectories was used: anterior (A), posterior (B), and lobar (C). Surgeons were classified based on experience with the MISTIE procedure as prequalified, qualified with probation, and fully qualified.

RESULTS

The average hematoma volume was 49.7 mL (range 20.0-124), and the mean evacuation rate was 71% (range 18.4%-99.8%). First placed catheters were 58% in good position, 28% suboptimal (but suitable to dose), and 14% poor (requiring repositioning). Posterior trajectory (B) was associated with significantly higher rates of poor placement (35%, P = .01). There was no significant difference in catheter placement accuracy among surgeons of varying experience. Hematoma evacuation efficacy was not significantly different among the 3 surgical approaches or different surgeons' experience.

CONCLUSION

Ongoing surgical education and quality monitoring in MISTIE III have resulted in consistent rates of hematoma evacuation despite technical challenges with the surgical approaches and among surgeons of varying experience.

Supraorbital vs Endo-Orbital Routes to the Lateral Skull Base: A Quantitative and Qualitative Anatomic Study

BACKGROUND

Various extensions of the supraorbital approach reach the lateral and parasellar middle cranial fossa regions by removing the orbital rim and greater/lesser sphenoid wings. Recent proposals of a purely endoscopic ventral transorbital pathway to these regions heighten the need to compare these surgical windows.

OBJECTIVE

To detail the lateral and parasellar middle cranial fossa regions and quantify exposures by 2 surgical windows (transcranial and transorbital) through anatomic study.

METHODS

In 5 cadaveric specimens (10 sides), dissections consisted of 3 stages: stage 1 began with the supraorbital approach via the eyebrow; stage 2, endo-orbital approach via the superior eyelid, continued with removal of lesser and greater sphenoid wings; and stage 3, extended supraorbital, re-evaluated the gains of stage 2 from the perspective of stage 1. Operative working areas were quantified in Sylvian, anterolateral temporal, and parasellar regions; bone removal volumes were measured at each stage (nonpaired Student t-test).

RESULTS

Visualization into the anterolateral temporal and Sylvian areas, though varied in perspective, were comparable with either eyelid or transcranial routes. Compared with transcranial views through a supraorbital window, the eyelid approach significantly increased exposure in the parasellar region with wider angle of attack (P &lt; .01) and achieved comparable bone removal volumes.

CONCLUSION

Stage 2’s unique anatomic view of the lateral and parasellar middle cranial fossa regions paves the way for possible surgical application to select pathologies typically treated via transcranial approaches. Disadvantages may be the surgeon's unfamiliarity with the anatomy of this purely endoscopic, ventral route and difficulties of dural and orbital repair.

Predicting symptomatic cerebral vasospasm after aneurysmal subarachnoid hemorrhage with an artificial neural network in a pediatric population

PURPOSE

Artificial neural networks (ANN) are increasingly applied to complex medical problem solving algorithms because their outcome prediction performance is superior to existing multiple regression models. ANN can successfully identify symptomatic cerebral vasospasm (SCV) in adults presenting after aneurysmal subarachnoid hemorrhage (aSAH). Although SCV is unusual in children with aSAH, the clinical consequences are severe. Consequently, reliable tools to predict patients at greatest risk for SCV may have significant value. We applied ANN modeling to a consecutive cohort of pediatric aSAH cases to assess its ability to predict SCV.

METHODS

A retrospective chart review was conducted to identify patients < 21 years of age who presented with spontaneously ruptured, non-traumatic, non-mycotic, non-flow-related intracranial arterial aneurysms to our institution between January 2002 and January 2015. Demographics, clinical, radiographic, and outcome data were analyzed using an adapted ANN model using learned value nodes from the adult aneurysmal SAH dataset previously reported. The strength of the ANN prediction was measured between - 1 and 1 with - 1 representing no likelihood of SCV and 1 representing high likelihood of SCV.

RESULTS

Sixteen patients met study inclusion criteria. The median age for aSAH patients was 15 years. Ten underwent surgical clipping and 6 underwent endovascular coiling for definitive treatment. One patient experienced SCV and 15 did not. The ANN applied here was able to accurately predict all 16 outcomes. The mean strength of prediction for those who did not exhibit SCV was - 0.86. The strength for the one patient who did exhibit SCV was 0.93.

CONCLUSIONS

Adult-derived aneurysmal SAH value nodes can be applied to a simple AAN model to accurately predict SCV in children presenting with aSAH. Further work is needed to determine if ANN models can prospectively predict SCV in the pediatric aSAH population in toto; adapted to include mycotic, traumatic, and flow-related origins as well.

Management of Arteriovenous Malformations Associated with Developmental Venous Anomalies: A Literature Review and Report of 2 Cases

BACKGROUND

Classification of cerebrovascular malformations has revealed intermediary lesions that warrant further review owing to their unusual presentation and management. We present 2 cases of arteriovenous malformation (AVM) associated with a developmental venous anomaly (DVA), and discuss the efficacy of previously published management strategies.

METHODS

Two cases of AVMs associated with DVA were identified, and a literature search for published cases between 1980 and 2016 was conducted. Patient demographic data and clinical features were documented.

RESULTS

In case 1, a 29-year-old female presenting with parenchymal hemorrhage and left homonymous hemianopia was found to have a right parieto-occipital AVM fed from the anterior cerebral, middle cerebral, and posterior cerebral arteries, with major venous drainage to the superior sagittal sinus. In case 2, imaging in a 34-year-old female evaluated for night tremors and incontinence revealed a left parietal AVM with venous drainage to the superior sagittal sinus. Including our 2 cases, 22 cases of coexisting AVMs and DVAs have been reported in the literature. At presentation, 68% had radiographic evidence of hemorrhage. Stereotactic radiosurgery was performed in 7 cases, embolization in 6 cases, surgical resection in 4 cases, and multimodal therapy in 5 cases. Radiography at follow-up demonstrated successful AVM obliteration in 67% of cases (12 of 18).

CONCLUSIONS

Patients with coexisting AVMs and DVAs tend to have a hemorrhagic presentation. Contrary to traditional AVM management, in these cases it is important to preserve the draining vein via the DVA to ensure a safe, sustained circulatory outflow of the associated brain parenchyma while achieving safe AVM obliteration.

The Interlenticulostriate Approach to Very High-Riding Distal Basilar Trunk Aneurysms

BACKGROUND

Most high-riding distal basilar trunk aneurysms can be surgically approached via the transsylvian route and its orbitozygomatic variant. However, on rare occasions, the basilar bifurcation may be unusually high and an approach above the carotid terminus may be required.

OBJECTIVE

In this cadaveric study, we sought to determine the feasibility and exposure limits of the interlenticulostriate approach (ILSA).

METHODS

A standard transsylvian approach was performed in 10 cerebral hemispheres of 5 formalin-fixed, silicone-injected cadaver heads. The interpeduncular cistern was exposed via the opticocarotid window, carotid-oculomotor window, and supracarotid ILSA window. The latter was measured and an aneurysm clip or ventriculostomy stylet was placed as high as possible through each corridor. Using noncontrast 3-D rotational angiography, clip/stylet positions were measured relative to the dorsum sellae.

RESULTS

ILSA provided a 9.4 × 4.6 mm mean surgical corridor, just enough room for a standard clip applier. This space was limited by the carotid bifurcation inferiorly, the lenticulostriate arteries medially and laterally, and the optic tract superiorly. There was no difference between opticocarotid and carotid-oculomotor windows, in terms of clip position (+8.9 vs +8.6 mm, respectively; P = .78). In contrast, ILSA provided significantly improved superior exposure, compared with either approaches (mean stylet position: +14.3 mm; P = .005). The exposure benefit afforded by ILSA was consistent across all 10 hemispheres, ranging from +2.5 to +8 mm.

CONCLUSION

For high-riding distal basilar trunk aneurysms that cannot be reached via the frontotemporal orbitozygomatic approach, ILSA can provide a viable route of access. Vascular neurosurgeons should be familiarized with this approach.

Thrombolytic removal of intraventricular haemorrhage in treatment of severe stroke: results of the randomised, multicentre, multiregion, placebo-controlled CLEAR III trial

BACKGROUND

Intraventricular haemorrhage is a subtype of intracerebral haemorrhage, with 50% mortality and serious disability for survivors. We aimed to test whether attempting to remove intraventricular haemorrhage with alteplase versus saline irrigation improved functional outcome.

METHODS

In this randomised, double-blinded, placebo-controlled, multiregional trial (CLEAR III), participants with a routinely placed extraventricular drain, in the intensive care unit with stable, non-traumatic intracerebral haemorrhage volume less than 30 mL, intraventricular haemorrhage obstructing the 3rd or 4th ventricles, and no underlying pathology were adaptively randomly assigned (1:1), via a web-based system to receive up to 12 doses, 8 h apart of 1 mg of alteplase or 0·9% saline via the extraventricular drain. The treating physician, clinical research staff, and participants were masked to treatment assignment. CT scans were obtained every 24 h throughout dosing. The primary efficacy outcome was good functional outcome, defined as a modified Rankin Scale score (mRS) of 3 or less at 180 days per central adjudication by blinded evaluators. This study is registered with ClinicalTrials.gov, NCT00784134.

FINDINGS

Between Sept 18, 2009, and Jan 13, 2015, 500 patients were randomised: 249 to the alteplase group and 251 to the saline group. 180-day follow-up data were available for analysis from 246 of 249 participants in the alteplase group and 245 of 251 participants in the placebo group. The primary efficacy outcome was similar in each group (good outcome in alteplase group 48% vs saline 45%; risk ratio [RR] 1·06 [95% CI 0·88-1·28; p=0·554]). A difference of 3·5% (RR 1·08 [95% CI 0·90-1·29], p=0·420) was found after adjustment for intraventricular haemorrhage size and thalamic intracerebral haemorrhage. At 180 days, the treatment group had lower case fatality (46 [18%] vs saline 73 [29%], hazard ratio 0·60 [95% CI 0·41-0·86], p=0·006), but a greater proportion with mRS 5 (42 [17%] vs 21 [9%]; RR 1·99 [95% CI 1·22-3·26], p=0·007). Ventriculitis (17 [7%] alteplase vs 31 [12%] saline; RR 0·55 [95% CI 0·31-0·97], p=0·048) and serious adverse events (114 [46%] alteplase vs 151 [60%] saline; RR 0·76 [95% CI 0·64-0·90], p=0·002) were less frequent with alteplase treatment. Symptomatic bleeding (six [2%] in the alteplase group vs five [2%] in the saline group; RR 1·21 [95% CI 0·37-3·91], p=0·771) was similar.

INTERPRETATION

In patients with intraventricular haemorrhage and a routine extraventricular drain, irrigation with alteplase did not substantially improve functional outcomes at the mRS 3 cutoff compared with irrigation with saline. Protocol-based use of alteplase with extraventricular drain seems safe. Future investigation is needed to determine whether a greater frequency of complete intraventricular haemorrhage removal via alteplase produces gains in functional status.

FUNDING

National Institute of Neurological Disorders and Stroke.

Abstract WP353: Bleeding Following Removal of Intracerebral Catheters in MISTIE III

Introduction: Minimally invasive surgery plus alteplase has been shown to effectively reduce the volume of intracerebral hemorrhage in patients with supratentorial bleeds. Removal of these catheters is a unique timepoint when bleeding may restart due to mechanical forces and/or the presence of alteplase/plasmin in the brain. We hypothesized that surgically-treated patients in the MISTIE III trial who had increased bleeding post catheter removal would have shorter periods of time between last dose and catheter removal and be less likely to have lobar ICH.

Methods: MISTIE III is a prospective, randomized trial testing the efficacy of minimally invasive surgery plus alteplase for hematoma removal compared to medical management. We analyzed 107 surgically-treated patients. Semi-automated threshold based segmentation of the ICH volumes for all time points were performed using OsiriX.

Results: Of the 107 surgical patients, 16 experienced an increase in ICH volume >10% between T1, the scan taken 24 hours prior to cath removal, and T2, the scan taken 24 hours post catheter removal. Mean percent difference between T1 and T2 was 37.5% for those that expanded versus those that did not, -17.4% (p<0.001) with an absolute difference in ICH volume of 3.0 cc and -2.2 cc (p<0.001). The mean residual volume at T2 for both groups was similar at 12.84 cc and 12.71 cc, respectively (p=0.96). Time from last dose to catheter removal in days was 1.27 for those that expanded and 1.44 for those that did not (p=0.09). Furthermore, 14/16 (87.5%) patients with expansion had ICH’s located in deep structures compared to 55/91 (60.4%) of patients that did not expand (p<0.01).

Conclusion: Overall, incidence of bleeding following ICH catheter removal in MISTIE III was low. When bleeding was seen, it was more often found in patients with deep ICH locations and whose catheters were removed sooner after the last dose of alteplase.

Stable incidence but declining case-fatality rates of subarachnoid hemorrhage in a population

OBJECTIVE

To characterize temporal trends in subarachnoid hemorrhage (SAH) incidence and outcomes over 5 time periods in a large population-based stroke study in the United States.

METHODS

All SAHs among residents of the Greater Cincinnati/Northern Kentucky region at least 20 years of age were identified and verified via study physician review in 5 distinct year-long study periods between 1988 and 2010. We abstracted demographics, care patterns, and outcomes, and we compared incidence and case-fatality rates across the study periods.

RESULTS

The incidence of SAH in the 5 study periods (age-, race-, and sex-adjusted to the 2000 US population) was 8.8 (95% confidence interval 6.8-10.7), 9.2 (7.2-11.2), 10.0 (8.0-12.0), 9.0 (7.1-10.9), and 7.7 (6.0-9.4) per 100,000, respectively; the trend in incidence rates from 1988 to 2010 was not statistically significant (p = 0.22). Advanced neurovascular imaging, endovascular coiling, and neurologic intensive care unit availability increased significantly over time. All-cause 5-day (32%-18%, p = 0.01; for trend), 30-day (46%-25%, p = 0.001), and 90-day (49%-29%, p = 0.001) case-fatality rates declined from 1988 to 2010. When we included only proven or highly likely aneurysmal SAH, the declines in case-fatality were no longer statistically significant.

CONCLUSIONS

Although the incidence of SAH remained stable in this population-based region, 5-day, 30-day, and 90-day case-fatality rates declined significantly. Advances in surgical and medical management, along with systems-based changes such as the emergence of neurocritical care units, are potential explanations for the reduced case-fatality.

Abstract TP365: Surgical Performance in Minimally Invasive Surgery Plus rt-PA for ICH Evacuation (MISTIE) Phase III Clinical Trial

Introduction: The MISTIE III trial aims to compare outcome following minimally invasive surgery plus thrombolysis versus best medical treatment for intracerebral hemorrhage (ICH). An image guided catheter is placed into the hematoma for ICH aspiration and rt-Pa administration. Surgeons at three levels of pre-specified experience with the procedure (pre-qualified PQ, qualified-probation QP, and fully qualified FQ) utilized one of three protocol-prescribed surgical approaches (anterior A, posterior B, and lobar C) based on the location and depth of the hematoma.

Objective: To assess accuracy of catheter placement and efficiency of ICH evacuation in relation to surgical approach and surgeon experience in the first 89 cases randomized to surgical treatment in the ongoing trial (roughly third of projected enrollments), with 86 cases undergoing the procedure.

Methods: The trial’s Surgical Center assessed prospectively the accuracy of initial catheter placement based on pre-articulated criteria, catheter replacement, and efficiency at ICH evacuation.

Results: Average ICH volume was 49.7ml at clot stability, with mean 72 % evacuated post catheter removal. Approaches A, B and C were used in 52, 25, and 23% of cases, with overall good, suboptimal and poor catheter placements in 58, 31 and 10 % of cases, respectively. Catheters were replaced/repositioned in 24 cases. Approach B was associated with significantly higher rates of poor placement (27%) and replacements (68%) than the other approaches (P< 0.01). Surgeon experience was PQ, QP and FQ in 56, 20, and 24% of cases, and was not associated with significantly different placement accuracy or replacement rates. Relative reduction in volume of the hematoma by the end of treatment was not significantly different among the three approaches, nor among surgeons at the three levels of experience.

Conclusion: Ongoing surgical education and quality monitoring in the MISTIE III trial have resulted in consistent rates of hematoma evacuation among surgeons of varying experience, and with different catheter trajectories, despite technical challenges with the posterior surgical approach. This documented optimization of the surgical task enhances the validity and subsequent generalizability of the ongoing trial.

Infundibular Hemangioblastoma in a Patient with Neurofibromatosis Type 1: Case Report and Review of the Literature

BACKGROUND

Supratentorial hemangioblastomas are rare tumors, most commonly occurring in the sellar/suprasellar region, cerebrum, and ventricle. They are generally found in patients with von Hippel Lindau disease but have infrequently been reported in patients without this syndrome.

CASE DESCRIPTION

A 35-year-old woman with a history of neurofibromatosis type 1 presented to our care with visual loss and headaches. Magnetic resonance imaging of the brain demonstrated an 8-mm cystic, contrast-enhancing lesion abutting the optic chiasm and optic tracts. The patient's endocrine profile was unremarkable. The tumor was resected using an endoscopic expanded transsphenoidal approach. Pathologic evaluation was consistent with hemangioblastoma. Postoperatively, the patient experienced an improvement in her visual symptoms.

CONCLUSIONS

Hemangioblastoma should be included in the differential of sellar/suprasellar mass lesions, particularly in patients with von Hippel Lindau disease. Small suprasellar lesions may be safely and effectively removed using an expanded transsphenoidal approach.

The role of microsurgical resection and radiosurgery for cerebral arteriovenous malformations

Cerebral arteriovenous malformations (AVMs) present unique challenges to cerebrovascular specialists. Management of these lesions begins with assessing their natural history. Intervention with the goal of complete obliteration requires some component of microsurgical techniques or radiosurgery. Clinicians must weigh observation and acceptance of the natural history of these lesions versus intervention on a case-by-case basis. Microsurgical resection and radiosurgery are both well-validated tools used in selectively treating cerebral AVMs. This manuscript offers a general review of the management of cerebral AVMs with multimodality treatment recommendations.

Beyond textbook neuroanatomy: The syndrome of malignant PCA infarction

Given its limited vascular territory, occlusion of the posterior cerebral artery (PCA) usually does not result in malignant infarction. Challenging this concept, we present 3 cases of unilateral PCA infarction with secondary malignant progression, resulting from extension into what would classically be considered the posterior middle cerebral artery (MCA) territory. Interestingly, these were true PCA infarctions, not "MCA plus" strokes, since the underlying occlusive lesion was in the PCA. We hypothesize that congenital and/or acquired variability in the distribution and extent of territory supplied by the PCA may underlie this rare clinical entity. Patients with a PCA infarction should thus be followed closely and offered early surgical decompression in the event of malignant progression.

Feasibility of the Ultrasonic Bone Aspirator in Retrosigmoid Vestibular Schwannoma Removal

Objective:

Postoperative headache is an undesirable consequence of retrosigmoid vestibular schwannoma (VS) removal. An ultrasonic bone aspirator (UBA) may reduce headache by minimizing subarachnoid bone dust dispersion. The feasibility of removing internal auditory canal (IAC) bone with a UBA is unknown. This study assessed volume and duration of IAC bone removal in clinical and laboratory settings.

Study Design:

(1) Retrospective review of radiologic data and intraoperative videos. (2) Cadaveric temporal bone model.

Setting:

(1) Tertiary care medical center. (2) Laboratory.

Subjects Methods:

We calculated the volume of IAC bone drilled during retrosigmoid VS removal using postoperative computed tomography scans. We then measured the time spent actively drilling IAC bone by analyzing operative videos. Finally, we measured bone ablation rates in a cadaveric temporal bone model using a drill and UBA.

Results:

The mean ± SD volume of IAC bone removed during surgery was 0.32 ± 0.17 mL (n = 9). The time spent actively removing IAC bone with a drill was only 10.4 ± 3.5 minutes, less than a third of the total IAC opening time of 34.2 ± 13.1 minutes (n = 5). On cadaveric specimens, the UBA removed bone at 0.21 ± 0.03 or 0.35 ± 0.07 µL/s at 15% or 50% power, respectively (n = 4). This extrapolates to 15.0 ± 3.0 to 25.0 ± 3.9 minutes to remove the same 0.32 mL from surgery.

Conclusions:

The volume and duration of IAC bone removal during retrosigmoid VS surgery are small. Using a UBA at low power instead of a drill would extend the length of surgery by 5 to 15 minutes, with the theoretical potential for reducing headache.

The extended transorbital craniotomy: an anatomic study

BACKGROUND

Supra-/transorbital approaches are mostly limited to suprasellar and anterior fossa pathologies, whereas lateral supraorbital approaches provide less retrosellar exposure and less overall operative volume, especially in the temporal region.

OBJECTIVE

Our cadaveric study proposes removal of the lesser and greater wings of the sphenoid bone to increase both the lateral angle typically achieved with pterional approaches and exposure to the temporal lobe and perisellar region.

METHODS

In 5 cadaveric specimens, our 3 steps to expand transorbital exposures included the following: step 1, standard transorbital craniotomy via a 3-cm supra-eyebrow incision; step 2, removal of the lesser sphenoid wing completed extradurally; and step 3, partial removal of the greater sphenoid wing. Operative extension in sylvian, parasellar, and anterolateral temporal exposures were quantified for each step (t test).

RESULTS

Step 2 provided the greatest increased exposure in the sylvian and parasellar regions compared with step 3, whereas step 3 provided a significant proportion of the exposure in the lateral temporal region. Finally, the lateral view progressively increased with each subsequent step.

CONCLUSION

Our 3-step removal of the lesser and greater wings of the sphenoid bone quantified increased sylvian, anterior temporal, and parasellar exposures for this minimally invasive approach with excellent cosmesis. Its increases the anterolateral view (similar to a subfrontal pterional approach) and offers potential applications to vascular and neoplastic (ie, sphenoid meningiomas) pathologies classically treated via a pterional or frontotemporal orbitozygomatic approach.