A Minimally Invasive Endovascular Approach to the Cerebellopontine Angle Cistern Enables Broad CNS Biodistribution of scAAV9-CB-GFP.

Neurological disorders pose a challenge for targeted therapy due to restricted access of therapeutic agents to the central nervous system (CNS). Current methods are limited by procedure-related risks, invasiveness, and insufficient CNS biodistribution. A novel percutaneous transvenous technology, currently in clinical trials for communicating hydrocephalus offers a minimally invasive approach by providing endovascular access to the cerebrospinal fluid-filled cerebellopontine angle (CPA) cistern. We hypothesized that drug delivery to the CPA cistern could yield widespread CNS distribution. Using an ovine model, we compared the biodistribution of scAAV9-CB-GFP following CPA cistern infusion with previously reported cisterna magna (CM) administration. Targeting both the CPA cistern and CM in sheep, we employed a lumbar spine-inserted microcatheter under fluoroscopy. CPA delivery of AAV9 demonstrated biodistribution and transduction in cerebral cortices, striatum, thalamus, midbrain, cerebellum, and spinal cord, with minor liver distribution comparable to CM. The favorable safety profile in humans with hydrocephalus suggests that percutaneous endovascular injection into the CPA could offer a clinically safer and minimally invasive delivery system for CNS gene and cell-based therapies.

Postoperative Hyponatremia After Endoscopic Endonasal Resection of Pituitary Adenomas: Historical Complication Rates and Risk Factors.

BACKGROUND: Hyponatremia is a common complication following endoscopic endonasal resection (EER) of pituitary adenomas. We report a single-center, multisurgeon study detailing baseline clinical data, outcomes, and factors associated with postoperative hyponatremia. METHODS: This was a retrospective cohort study of patients undergoing EER for pituitary adenoma at Tufts Medical Center. Most procedures were performed by the senior author (C.B.H.). Cases were included if at least 1 postoperative sodium value was available and pathology confirmed pituitary adenoma. Hyponatremia was defined as a postoperative sodium level <135 mEq/L. RESULTS: A total of 272 patients underwent 310 EER procedures that met the study inclusion criteria. The mean patient age was 53.3 years, and mean tumor size was 18.8 mm. Postoperative hyponatremia occurred in 12.6% of cases, with 3.6% developing hyponatremia prior to discharge. Lower preoperative sodium level was associated with an increased risk of developing any postoperative hyponatremia. Older age, prolactinoma pathology, and use of selective serotonin reuptake inhibitors were associated with moderate to severe hyponatremia (≤129 mEq/L), and lower preoperative sodium was associated with mild hyponatremia (130-134 mEq/L). Hyponatremia-related readmissions within 30 days occurred in 3.9% of patients. Both African-American race and postoperative hyponatremia were associated with an increased risk of 30-day readmission. The mean nadir sodium for hyponatremic patients was 129.9 mEq/L. Growth hormone-secreting pathology was associated with lower postoperative nadir sodium, whereas higher preoperative sodium was associated with higher postoperative nadir sodium. CONCLUSIONS: Hyponatremia is a common postoperative complication of EER for pituitary lesions that can cause significant morbidity, increased readmissions, and increased healthcare costs.

Endovascular Shunting for Communicating Hydrocephalus Using a Biologically Inspired Transdural Cerebrospinal Fluid Valved eShunt® Implant.

Cerebrospinal fluid (CSF) bathing the central nervous system is produced by brain and choroid plexus within the ventricles for re-absorption into the venous circulation through arachnoid granulations (AG). Communicating hydrocephalus results from disruption of the absorptive process, necessitating surgical catheter-based shunt placement to relieve excess pressure from CSF buildup. Adjustable valve designs and antibiotic impregnation have minimally impacted persistent failure rates and postoperative complications. To confront this challenge, we have developed an innovative endovascular shunt implant biologically inspired from AG function to restore the natural dynamics of CSF drainage while concurrently addressing the predominant factors contributing to conventional shunt malfunction.

The History of Superior Semicircular Canal Dehiscence: A Bibliometric Analysis.

OBJECTIVE: The treatment and understanding of superior semicircular canal dehiscence (SSCD) has seen significant developments over the past 25 years. Bibliographic analysis can provide insight into the evolution of research as well as highlight emerging areas. Reviewing a large volume of publications provides valuable insights into the citation patterns and collaborations of research groups. This study seeks to offer a comprehensive historical overview of SSCD and leading authors. DATABASE REVIEWED: Web of Science Core Collection. METHODS: A bibliometric analysis of the current literature on SSCD was conducted. A performance analysis and science mapping of the top 100 most cited articles was completed using a citation analysis. Two independent reviewers evaluated articles for relevance and adjugated by a third reviewer. Author and institution networks were examined. RESULTS: Seven hundred ninety-one articles on the topic of SSCD were identified. The top 100 articles spanned over 23 years from 1998 to 2019 and were published in 30 different journals. The top 100 articles were cited 8253 times in literature. The document contents revealed 233 keywords and 238 author keywords. The articles were authored by a total of 291 authors, with only 4 single-authored documents. CONCLUSIONS: SSCD has been highly researched in aspects of symptomatology, diagnosis, and treatment, as indicated by many highly cited articles that relate. However, the production of highly cited articles on SSCD displays a significant decrease after 2013, with only 17 of the top cited articles published since then.

Open Surgical Obliteration of Three Indirect Carotid-Cavernous Fistulas.

BACKGROUND AND IMPORTANCE: Carotid-cavernous fistulas (CCFs) are abnormal connections between the carotid artery and the cavernous sinus (CS). CCFs are primarily treated by an endovascular route, but there are situations in which a lesion is not amenable to endovascular or transorbital treatment, necessitating a transcranial approach. In this select group of patients, the use of crushed temporalis muscle to pack the CS fistula site was found to be an effective method for treatment of CCFs. CLINICAL PRESENTATION: In this case series, we present 3 patients with CCFs in which endovascular treatment was not possible because of occlusion of the petrosal sinuses or stenosis of the superior ophthalmic vein at the superior orbital fissure, rendering the lesion inaccessible by a transvenous or transorbital route. Each patient was treated with a variation of temporalis muscle packing through a skull base triangle; one was treated through the anteromedial triangle, one through the supratrochlear triangle, and the third through the Parkinson triangle. The fistulas were cured in each case. CONCLUSION: Cavernous-carotid fistulas that are not amenable to endovascular or transorbital treatment can be successfully treated by packing the CS fistula site with crushed temporalis muscle. To cure these patients' symptoms and enhance their quality of life, it is crucial to weigh the advantages and disadvantages of each therapy option.

Strangulation of the abducens nerve by an arachnoid band within an epidermoid cyst: illustrative case.

BACKGROUND: Intracranial epidermoid cysts (ECs) are rare benign lesions of ectodermal origin that can be found in the cerebellopontine angle (CPA). If large enough, they compress surrounding structures, causing cranial neuropathies, cerebellar dysfunction, and hydrocephalus. OBSERVATIONS: In this case report, the authors present a patient with headaches and diplopia secondary to a CPA EC. The cyst had wrapped itself around and was strangulating the abducens nerve. This choking of the nerve was believed to have been the cause of the patient's double vision. The arachnoid band was released with a myringotomy knife. LESSONS: Intracranial ECs typically cause symptoms from mass effect on surrounding structures; it is unusual for one to have choked off the nerve in the fashion presented in this case. Knowledge of the potential ways that ECs can affect nervous structures is critical for resecting them without injuring normal tissue.

International Tuberculum Sellae Meningioma Study: Preoperative Grading Scale to Predict Outcomes and Propensity-Matched Outcomes by Endonasal Versus Transcranial Approach.

BACKGROUND AND OBJECTIVES: Tuberculum sellae meningiomas are resected via an expanded endonasal (EEA) or transcranial approach (TCA). Which approach provides superior outcomes is debated. The Magill-McDermott (M-M) grading scale evaluating tumor size, optic canal invasion, and arterial involvement remains to be validated for outcome prediction. The objective of this study was to validate the M-M scale for predicting visual outcome, extent of resection (EOR), and recurrence, and to use propensity matching by M-M scale to determine whether visual outcome, EOR, or recurrence differ between EEA and TCA. METHODS: Forty-site retrospective study of 947 patients undergoing tuberculum sellae meningiomas resection. Standard statistical methods and propensity matching were used. RESULTS: The M-M scale predicted visual worsening (odds ratio [OR]/point: 1.22, 95% CI: 1.02-1.46, P = .0271) and gross total resection (GTR) (OR/point: 0.71, 95% CI: 0.62-0.81, P < .0001), but not recurrence ( P = .4695). The scale was simplified and validated in an independent cohort for predicting visual worsening (OR/point: 2.34, 95% CI: 1.33-4.14, P = .0032) and GTR (OR/point: 0.73, 95% CI: 0.57-0.93, P = .0127), but not recurrence ( P = .2572). In propensity-matched samples, there was no difference in visual worsening ( P = .8757) or recurrence ( P = .5678) between TCA and EEA, but GTR was more likely with TCA (OR: 1.49, 95% CI: 1.02-2.18, P = .0409). Matched patients with preoperative visual deficits who had an EEA were more likely to have visual improvement than those undergoing TCA (72.9% vs 58.4%, P = .0010) with equal rates of visual worsening (EEA 8.0% vs TCA 8.6%, P = .8018). CONCLUSION: The refined M-M scale predicts visual worsening and EOR preoperatively. Preoperative visual deficits are more likely to improve after EEA; however, individual tumor features must be considered during nuanced approach selection by experienced neurosurgeons.

International Tuberculum Sellae Meningioma Study: Surgical Outcomes and Management Trends.

BACKGROUND AND OBJECTIVES: Tuberculum sellae meningiomas (TSMs) can be resected through transcranial (TCA) or expanded endonasal approach (EEA). The objective of this study was to report TSM management trends and outcomes in a large multicenter cohort. METHODS: This is a 40-site retrospective study using standard statistical methods. RESULTS: In 947 cases, TCA was used 66.4% and EEA 33.6%. The median maximum diameter was 2.5 cm for TCA and 2.1 cm for EEA ( P < .0001). The median follow-up was 26 months. Gross total resection (GTR) was achieved in 70.2% and did not differ between EEA and TCA ( P = .5395). Vision was the same or better in 87.5%. Vision improved in 73.0% of EEA patients with preoperative visual deficits compared with 57.1% of TCA patients ( P < .0001). On multivariate analysis, a TCA (odds ratio [OR] 1.78, P = .0258) was associated with vision worsening, while GTR was protective (OR 0.37, P < .0001). GTR decreased with increased diameter (OR: 0.80 per cm, P = .0036) and preoperative visual deficits (OR 0.56, P = .0075). Mortality was 0.5%. Complications occurred in 23.9%. New unilateral or bilateral blindness occurred in 3.3% and 0.4%, respectively. The cerebrospinal fluid leak rate was 17.3% for EEA and 2.2% for TCA (OR 9.1, P < .0001). The recurrence rate was 10.9% (n = 103). Longer follow-up (OR 1.01 per month, P < .0001), World Health Organization II/III (OR 2.20, P = .0262), and GTR (OR: 0.33, P < .0001) were associated with recurrence. The recurrence rate after GTR was lower after EEA compared with TCA (OR 0.33, P = .0027). CONCLUSION: EEA for appropriately selected TSM may lead to better visual outcomes and decreased recurrence rates after GTR, but cerebrospinal fluid leak rates are high, and longer follow-up is needed. Tumors were smaller in the EEA group, and follow-up was shorter, reflecting selection, and observation bias. Nevertheless, EEA may be superior to TCA for appropriately selected TSM.

The New England Neurosurgical Society: growth and evolution over 70 years.

The New England Neurosurgical Society (NENS) was founded in 1951 under the leadership of its first President (Dr. William Beecher Scoville) and Secretary-Treasurer (Dr. Henry Thomas Ballantine). The purpose of creating the NENS was to unite local neurosurgeons in the New England area; it was one of the first regional neurosurgical societies in America. Although regional neurosurgical societies are important supplements to national organizations, they have often been overshadowed in the available literature. Now in its 70th year, the NENS continues to serve as a platform to represent the needs of New England neurosurgeons, foster connections and networks with colleagues, and provide research and educational opportunities for trainees. Additionally, regional societies enable discussion of issues uniquely relevant to the region, improve referral patterns, and allow for easier attendance with geographic proximity. In this paper, the authors describe the history of the NENS and provide a roadmap for its future. The first section portrays the founders who led the first meetings and establishment of the NENS. The second section describes the early years of the NENS and profiles key leaders. The third section discusses subsequent neurosurgeons who steered the NENS and partnerships with other societies. In the fourth section, the modern era of the NENS and its current activities are highlighted.

Cavernous segment internal carotid artery stenosis specific to meningiomas compared to pituitary adenomas.

BACKGROUND AND PURPOSE: Pituitary macroadenomas and meningiomas are common neoplasms arising within the cavernous sinus. Imaging characteristics on MRI can often distinguish these tumors from one another; however, some cases may be more difficult to differentiate. This study compares patterns of cavernous segment internal carotid artery (CS-ICA) stenosis between the two tumor types to establish a novel radiographic method of differentiation. METHODS: A retrospective analysis of patients with pathology-confirmed meningioma and pituitary adenomas at Tufts Medical Center was performed. The diameter of the CS-ICA at the narrowest point within the cavernous sinus was measured and compared to the ipsilateral petrous segment ICA and contralateral CS-ICA. The mean and range of percent stenosis and frequency of cases of CS-ICA stenosis >15% were determined. Statistical analysis to compare the groups was conducted using the Chi-squared test, Fisher's exact test, and t-test. RESULTS: There were a total of 78 out of 231 patients who were included in the study. The mean % ICA stenosis for all meningiomas was 9.3%, with increasing stenosis with increasing World Health Organization grade. Of all meningioma cases, 13 (33%) had greater than 15% ICA stenosis. Mean ICA stenosis for pituitary adenomas was -1.48%. There were no cases of pituitary adenomas causing ICA stenosis >15%. CONCLUSIONS: Differentiating pituitary adenomas and intracavernous meningioma tumors can have important implications on surgical approach and outcome. Our study found that stenosis of the CS-ICA greater than 15% is highly specific to meningiomas and can serve as a radiologic sign to distinguish between these two tumors.

Primary Spinal Cord Astrocytomas: Two-Center Clinical Experience of Low- and High-Grade Lesions.

OBJECTIVE: Primary spinal cord astrocytomas are rare, fatal, and poorly studied. METHODS: This study included a 2-center, retrospective analysis of primary spinal cord astrocytoma patients from 1997 to 2020. Patients with drop metastases or without at least one follow-up were excluded. RESULTS: Seven World Health Organization grade I, 6 grade II, 7 grade III, and 4 grade IV astrocytoma patients were included. Older patients had higher grades (median 20 years in grade I vs. 36.5 in grade IV). The median follow-up was 15 months. Thirteen patients were discharged to rehabilitation. Eight patients demonstrated radiographic progression. Adjuvant therapy was utilized more in higher grades (5 of 13 grades III vs. all 11 grades IIIIV). Six patients died (1 death in grades III vs. 5 in grades IIIIV). Ten patients had worsened symptoms at the last follow-up. The median progression-free survival in grade I, II, III, and IV tumors was 116, 36, 8, and 8.5 months, respectively. The median overall survival in grade I, II, III, and IV tumors was 142, 69, 19, and 12 months, respectively. Thrombotic complications occurred in 2 patients, one with isocitrate dehydrogenasewild type glioblastoma. CONCLUSIONS: Outcomes worsen with higher grades and lead to difficult postoperative periods. Clinicians should be vigilant for thromboembolic complications. Further research is needed to understand these rare tumors.

Retrosigmoid Craniectomy with a Layered Soft Tissue Dissection and Hydroxyapatite Reconstruction: Technical Note, Surgical Video, Regional Anatomy, and Outcomes.

Introduction There are many reported modifications to the retrosigmoid approach including variations in skin incisions, soft tissue dissection, bone removal/replacement, and closure. Objective The aim of this study was to report the technical nuances developed by two senior skull base surgeons for retrosigmoid craniectomy with reconstruction and provide anatomic dissections, surgical video, and outcomes. Methods The regional soft tissue and bony anatomy as well as the steps for our retrosigmoid craniectomy were recorded with photographs, anatomic dissections, and video. Records from 2017 to 2019 were reviewed to determine the incidence of complications after the authors began using the described approach. Results Dissections of the relevant soft tissue, vascular, and bony structures were performed. Key surgical steps are (1) a retroauricular C-shaped skin incision, (2) developing a skin and subgaleal tissue flap of equal thickness above the fascia over the temporalis and sub-occipital muscles, (3) creation of subperiosteal soft tissue planes over the top of the mastoid and along the superior nuchal line to expose the suboccipital region, (4) closure of the craniectomy defect with in-lay titanium mesh and overlay hydroxyapatite cranioplasty, and (5) reapproximation of the soft tissue edges during closure. Complications in 40 cases were pseudomeningocele requiring shunt ( n = 3, 7.5%), wound infection ( n = 1, 2.5%), and aseptic meningitis ( n = 1, 2.5%). There were no incisional cerebrospinal fluid leaks. Conclusion The relevant regional anatomy and a revised technique for retrosigmoid craniectomy with reconstruction have been presented with acceptable results. Readers can consider this technique when using the retrosigmoid approach for pathology in the cerebellopontine angle.

First-in-human endovascular treatment of hydrocephalus with a miniature biomimetic transdural shunt.

Surgical ventriculoperitoneal shunting remains standard treatment for communicating hydrocephalus, despite persistently elevated infection and revision rates. A novel minimally invasive endovascular cerebrospinal fluid (CSF) shunt was developed to mimic the function of the arachnoid granulation which passively filters CSF from the central nervous system back into the intracranial venous sinus network. The endovascular shunt is deployed via a femoral transvenous approach across the dura mater into the cerebellopontine angle cistern. An octogenarian with intractable hydrocephalus following subarachnoid hemorrhage underwent successful endovascular shunting, resulting in swift intracranial pressure reduction from 38 to <20 cmH2O (<90 min) and resolution of ventriculomegaly. This first successful development of a percutaneous transluminal venous access to the central nervous system offers a new pathway for non-invasive treatment of hydrocephalus and the potential for intervention against neurological disorders.

Endoscopic Endonasal Versus Transoral Odontoidectomy for Non-Neoplastic Craniovertebral Junction Disease: A Case Series.

BACKGROUND: Odontoidectomy is a challenging yet effective operation for decompression of non-neoplastic craniovertebral junction disease. Though both the endoscopic endonasal approach (EEA) and the transoral approach (TOA) have been discussed in the literature, there remain few direct comparisons between the techniques. OBJECTIVE: To evaluate the perioperative outcomes of EEA vs TOA odontoidectomy. METHODS: A retrospective review of all cases undergoing odontoidectomy by either the EEA or TOA was performed. Attention was paid to the need for prolonged nutritional support, prolonged respiratory support, and hospitalization times. RESULTS: During the study period between 2000 and 2018, 25 patients underwent odontoid process resection (18 TOA and 7 EEA). The most common indication for surgery was basilar invagination. Hospital length of stay, intensive care unit length of stay, and intubation days were all significantly shorter in the EEA group compared to the TOA group (P < .01, P = .01, P < .01, respectively). Prolonged nutritional support in the form of a gastrostomy tube was required in 5 patients and tracheostomy was required in 4 patients; all of these underwent odontoidectomy by the TOA. There was no statistical difference in neurological outcomes between the EEA and TOA groups (P = .17). CONCLUSION: Odontoidectomy can be performed safely through both the EEA and TOA. The results of this study suggest the EEA has shorter hospitalizations and a lower probability of requiring prolonged nutritional support. These advantages are likely the results of decreased oropharyngeal mucosa disruption as compared to the TOA.

Clinical and histopathological principles for the diagnosis of a recurrent paraganglioma of the jugular foramen initially diagnosed as a middle ear adenoma: illustrative case.

BACKGROUND: Paragangliomas (PGLs) are rare neoplasms that may be associated with hereditary PGL syndromes and variable risk of metastasis. Middle ear adenomas are extremely rare tumors with no known hereditary predisposition and extremely low risk of metastasis. Although often easily differentiated, they may share clinical and pathological features that misdirect and confuse the diagnosis. OBSERVATIONS: The authors discussed a 35-year-old woman with left-sided hearing loss and bleeding from the external ear canal who presented to an outside hospital. She underwent resection of a middle ear and mastoid mass, initially diagnosed as a middle ear adenoma with neuroendocrine features, with later mastoidectomy and ligation of the sigmoid sinus with microsurgical excision of persistent tumor in the jugular foramen and temporal bone. Histopathologically, her tumor was vascular, composed of benign-appearing epithelioid cells with "salt and pepper" neuroendocrine chromatin arranged in vague nests. Lesional cells were GATA3-immunopositive, glucagon-negative, and succinate dehydrogenase-immunonegative, consistent with PGL rather than middle ear adenoma, and required further workup for hereditary PGL syndromes. LESSONS: This case demonstrates potential challenges in differentiating a PGL from a middle ear adenoma. The authors offer clinical, histopathological, and imaging principles to aid in diagnosis and workup.

Primary meningeal melanoma masquerading as neurofibromatosis type 2: illustrative case.

BACKGROUND: Primary meningeal melanocytic neoplasms are exceedingly rare tumors, representing only 0.06% to 0.1% of all primary brain tumors and ranging in spectrum from benign localized tumors to highly aggressive malignant lesions. The diagnosis of these tumors is often challenging from clinical, radiological, and pathologic standpoints. Equally challenging is the distinction between primary meningeal melanocytic neoplasm and metastatic melanoma. OBSERVATIONS: The authors reported the case of a 41-year-old man with imaging findings diagnostic of neurofibromatosis type 2: bilateral internal auditory canal lesions (most consistent with bilateral vestibular schwannomas), two dura-based lesions presumed to be meningiomas, multiple spinal lesions consistent with peripheral nerve sheath tumors, and one intramedullary spinal lesion consistent with an ependymoma. Biopsy of these lesions revealed melanocytic neoplasms with mild to moderate atypia and a mildly elevated proliferation index, which made the distinction between benign and malignant challenging. In addition, the disseminated nature of these tumors made it difficult to determinate whether they arose from the meninges or represented metastases from an occult primary melanoma. LESSONS: This case illustrated the challenges presented by the diagnosis of meningeal melanocytic neoplasms and highlighted the importance of integrating the clinical and radiographic findings with histologic appearance and molecular studies.

Continuous improvement in patient safety and quality in neurological surgery: the American Board of Neurological Surgery in the past, present, and future.

The American Board of Neurological Surgery (ABNS) was incorporated in 1940 in recognition of the need for detailed training in and special qualifications for the practice of neurological surgery and for self-regulation of quality and safety in the field. The ABNS believes it is the duty of neurosurgeons to place a patient's welfare and rights above all other considerations and to provide care with compassion, respect for human dignity, honesty, and integrity. At its inception, the ABNS was the 13th member board of the American Board of Medical Specialties (ABMS), which itself was founded in 1933. Today, the ABNS is one of the 24 member boards of the ABMS.To better serve public health and safety in a rapidly changing healthcare environment, the ABNS continues to evolve in order to elevate standards for the practice of neurological surgery. In connection with its activities, including initial certification, recognition of focused practice, and continuous certification, the ABNS actively seeks and incorporates input from the public and the physicians it serves. The ABNS board certification processes are designed to evaluate both real-life subspecialty neurosurgical practice and overall neurosurgical knowledge, since most neurosurgeons provide call coverage for hospitals and thus must be competent to care for the full spectrum of neurosurgery.The purpose of this report is to describe the history, current state, and anticipated future direction of ABNS certification in the US.

Facial nerve outcomes following gamma knife radiosurgery for subtotally resected vestibular schwannomas: Early versus delayed timing of therapy.

OBJECTIVES: Initially treating vestibular schwannomas (VSs) with subtotal resection (STR) followed by Gamma Knife radiosurgery (GKRS) for progression of tumor residual is a strategy that balances maximal tumor resection with preservation of neurological function. The effect of timing of GKRS for residual and recurrent VSs remains poorly defined. We developed a simple and practical treatment algorithm for the timing of GKRS after STR of VSs and reviewed our follow-up results to determine outcomes between patients treated with early vs. late GKRS. PATIENTS AND METHODS: Patients that underwent STR between 1999 and 2017 for a VS at Tufts Medical Center were identified and included in the study cohort. Patients who received GKRS ≤ 12 months after STR were included in the early intervention group. Patients who received GKRS > 12 months after STR or did not have tumor progression on follow-up thus not requiring GKRS were included in the observation/delayed intervention group. RESULTS: STR of VSs was performed on 23 patients. Mean patient age at the time of STR was 53.0 years (range: 20-86.2). The mean follow-up was 4.2 years (range: 1 month-15.5 years). Patients most frequently presented with hearing loss. There were 5 patients (21.7 %) in the early intervention group and 18 (78.3 %) patients in the observation/delayed intervention group. Ten of 23 patients (43.5 %) required GKRS. Thirteen (56.5 %) did not receive GKRS. None of the patients in the early intervention group or the observation/delayed intervention group had changes in House-Brackmann (HB) Grade either after GKRS or at the end of the study period. CONCLUSIONS: GKRS of residual or recurrent tumor is safe following STR of VS and appears to carry a low risk of worsening facial nerve function when performed for progressive tumor growth.