Interplay between vascular hemodynamics and the glymphatic system in the pathogenesis of idiopathic normal pressure hydrocephalus, exploring novel neuroimaging diagnostics.

As the aging population continues to grow, so will the incidence of age-related conditions, including idiopathic normal pressure hydrocephalus (iNPH). The pathogenesis of iNPH remains elusive, and this is due in part to the poor characterization of cerebral spinal fluid (CSF) dynamics within the brain. Advancements in technology and imaging techniques have enabled new breakthroughs in understanding CSF physiology, and therefore iNPH pathogenesis. This includes understanding the hemodynamic and microvascular components involved in CSF influx and flow. Namely, the glymphatic system appears to be the great mediator, facilitating perivascular CSF flow via astrocytic aquaporin channels located along the endothelium of the pial vasculature. The interplay between glymphatics and both arterial pulsatilty and venous compliance has also been recently demonstrated. It appears then that CSF flow, and therefore glymphatic function, are highly dependent on cardiocirculatory and vascular factors. Impairment in any one component, whether it be related to arterial pulsatility, microvascular changes, reduced venous drainage, or astrogliosis, contributes greatly to iNPH, although it is likely a combination thereof. The strong interplay between vascular hemodynamics and CSF flow suggests perfusion imaging and cerebral blood flow quantification may be a useful diagnostic tool in characterizing iNPH. In addition, studies detecting glymphatic flow with magnetic resonance imaging have also emerged. These imaging tools may serve to both diagnose iNPH and help delineate it from other similarly presenting disease processes. With a better understanding of the vascular and glymphatic factors related to iNPH pathogenesis, physicians are better able to select the best candidates for treatment.

The SMART Registry: Long-Term Results on the Utility of the Penumbra SMART COIL System for Treatment of Intracranial Aneurysms and Other Malformations.

Introduction: Penumbra SMART COIL® (SMART) System is a novel generation embolic coil with varying stiffness. The study purpose was to report real-world usage of the SMART System in patients with intracranial aneurysms (ICA) and non-aneurysm vascular lesions. Materials and Methods: The SMART Registry is a post-market, prospective, multicenter registry requiring ≥75% Penumbra Coils, including SMART, PC400, and/or POD coils. The primary efficacy endpoint was retreatment rate at 1-year and the primary safety endpoint was the procedural device-related serious adverse event rate. Results: Between June 2016 and August 2018, 995 patients (mean age 59.6 years, 72.1% female) were enrolled at 68 sites in the U.S. and Canada. Target lesions were intracranial aneurysms in 91.0% of patients; 63.5% were wide-neck and 31.8% were ruptured. Adjunctive devices were used in 55.2% of patients. Mean packing density was 32.3%. Procedural device-related serious adverse events occurred in 2.6% of patients. The rate of immediate post-procedure adequate occlusion was 97.1% in aneurysms and the rate of complete occlusion was 85.2% in non-aneurysms. At 1-year, the retreatment rate was 6.8%, Raymond Roy Occlusion Classification (RROC) I or II was 90.0% for aneurysms, and Modified Rankin Scale (mRS) 0-2 was achieved in 83.1% of all patients. Predictors of 1-year for RROC III or retreatment (incomplete occlusion) were rupture status (P < 0.0001), balloon-assisted coiling (P = 0.0354), aneurysm size (P = 0.0071), and RROC III immediate post-procedure (P = 0.0086) in a model that also included bifurcation aneurysm (P = 0.7788). Predictors of aneurysm retreatment at 1-year was rupture status (P < 0.0001). Conclusions: Lesions treated with SMART System coils achieved low long-term retreatment rates. Clinical Trial Registration: https://www.clinicaltrials.gov/, identifier NCT02729740.

Dural venous sinus stenting for treatment of pediatric idiopathic intracranial hypertension.

BACKGROUND: Dural venous sinus stenting (VSS) is an effective treatment for idiopathic intracranial hypertension (IIH) in adult patients. There are no published series to date evaluating safety and efficacy of VSS in pediatric patients. OBJECTIVE: To report on procedural device selection and technique as well as safety and efficacy of VSS for pediatric patients with medically refractory IIH due to underlying venous sinus stenosis. METHODS: A multi-institutional retrospective case series identified patients with medically refractory IIH aged less than 18 years who underwent VSS. RESULTS: 14 patients were identified at four participating centers. Patient ages ranged from 10 to 17 years, and 10 patients (71.4%) were female. Mean body mass index was 25.7 kg/m2 (range 15.8-34.6 kg/m2). Stenting was performed under general endotracheal anesthesia in all except two patients. The average trans-stenotic gradient during diagnostic venography was 10.6 mm Hg. Patients had stents placed in the superior sagittal sinus, transverse sinus, sigmoid sinus, occipital sinus, and a combination. Average follow-up was 1.7 years after stenting. Six patients out of 10 (60%) had reduced medication dosing, 12 of 14 patients (85.7%) had improvements in headaches, two patients (100%) with pre-stent tinnitus had resolution of symptoms, and four (80%) of five patients with papilledema had improvement on follow-up ophthalmological examinations. Two patients (14.3%) developed postprocedural groin hematomas, one patient (7.1%) developed a groin pseudoaneurysm, and one patient (7.1%) had postprocedural groin bleeding. No other procedural complications occurred. Four patients (28.6%) required further surgical treatment (cerebrospinal shunting and/or stenting) after their first stenting procedure. CONCLUSIONS: This series suggests that VSS is feasible in a pediatric population with IIH and has a low complication rate and good clinical outcomes.

Microvascular decompression of the posterior cerebral artery for treatment of oculomotor nerve palsy.

Oculomotor nerve palsy resulting from non-aneurysmal vascular compression is extremely rare. Microvascular decompression (MVD) has been previously shown to improve oculomotor nerve palsy (ONP) secondary to arterial compression. A 71-year-old female, with a history of Cushing's disease previously treated with two transsphenoidal resections and Gamma Knife radiosurgery, presented with one year of progressive left eye diplopia and was diagnosed with a partial left oculomotor nerve palsy. We performed an orbitozygomatic craniotomy for MVD of the left posterior cerebral artery, which was found to be compressing the oculomotor nerve against the tentorium. Unfortunately, the patient's partial ONP remained unchanged at one year follow-up. The present case suggests inconsistent outcomes of MVD for ONP. Patients with prior sellar or parasellar irradiation may be less likely to benefit from this treatment approach.

Idiopathic Intracranial Hypertension Masking as Obstructive Hydrocephalus: A Case Report.

Idiopathic intracranial hypertension (IIH) is a poorly understood phenomenon and its presentation can both mimic and co-exist with other intra-cranial processes. Accurate diagnosis is imperative as ongoing advancements in treatment can yield dramatic positive results. Here we present the case of an individual with signs and symptoms of obstructive hydrocephalus who was ultimately found to have IIH secondary to venous sinus stenosis. After correction of the venous sinus stenosis, resolution in the patient's symptoms was noted. The case highlights some of the unique considerations in approaching patients with IIH and provides a framework for review of current literature related to IIH and venous sinus stenosis.

Concurrent Venous Stenting of the Transverse and Occipito-Marginal Sinuses: An Analogy with Parallel Hemodynamic Circuits.

Nonthrombotic intracranial venous occlusive disease (NIVOD) has been implicated in the pathophysiology of idiopathic intracranial hypertension (IIH) and various non-IIH headache syndromes. Endovascular stenting of stenotic, dominant transverse sinuses (TSs) may reduce trans-stenosis pressure gradients, decrease intracranial pressure, and alleviate symptoms in a subset of NIVOD patients. We present a case in which concurrent stenting of the occipito-marginal sinus obliterated the residual trans-stenosis pressure gradient across an initially stented dominant TS. We hypothesize that this observation may be explained using an electric-hydraulic analogy, and that this patient's dominant TS and occipito-marginal sinus may be modeled as a parallel hemodynamic circuit. Neurointerventionalists should be aware of parallel hemodynamic drainage patterns and consider manometry and possibly additional stenting of stenotic, parallel venous outflow pathways if TS stenting alone fails to obliterate the trans-stenosis pressure gradient.

Intracranial Venous Sinus Stenting: A Review of Idiopathic Intracranial Hypertension and Expanding Indications.

Idiopathic intracranial hypertension (IIH) is a functionally limiting disorder secondary to increased intracranial pressures (ICPs) with a prevalence of one per 100,000 persons. It is estimated to cost >$400 million per year in productively. Symptoms classically consist of chronic headaches, papilledema, and visual loss. The pathophysiology is unknown but postulated to involve increased resistance to cerebrospinal fluid (CSF) absorption. Traditional treatments involve weight loss, acetazolamide, CSF diversion, or optic nerve fenestration. More recent technology has allowed exploration of venous sinus stenosis. Through venous sinus stenting (VSS), the ICPs and venous sinus pressures decrease. After treatment, >75% exhibit an improvement in headaches, ~50% improvement in tinnitus, and ~50 % improvement in ophthalmologic testing. Complications are rare but involve stent stenosis, femoral pseudoaneurysm, and hemorrhages. Future studies will look into controlled studies for VSS as well as expansion to other venous structures of the intracranial circulation.

High-Grade Aneurysmal Subarachnoid Hemorrhage: Predictors of Functional Outcome.

BACKGROUND: Because the prognosis of high-grade aneurysmal subarachnoid hemorrhage (aSAH), classified as World Federation of Neurosurgical Societies (WFNS) grade IV-V, is generally poor, the functional outcomes of survivors have not been thoroughly explored. The aim of this retrospective cohort study is to determine predictors of functional independence in patients who survive a high-grade aSAH. METHODS: We retrospectively evaluated consecutive patients with aSAH admitted to a single institution from January 2000 to April 2015. Adult (age ≥18 years) patients with WFNS grade IV-V aSAH were included for analysis. Patients without sufficient baseline data, those who died before discharge, and those without follow-up data were excluded. Univariable and multivariable logistic regression analyses were used to identify factors associated with functional independence, defined as a modified Rankin Scale score of 0-2, at last follow-up. RESULTS: Of the 260 patients with a WFNS grade IV-V aSAH during the study period, 139 met the inclusion criteria. After a mean follow-up of 6.3 months, functional independence was achieved in 73% of high-grade aSAH survivors (101/139 patients) and in 39% of all high-grade aSAH cases (101/260 patients). Only a lack of cerebrospinal fluid shunt placement was found to be an independent predictor of functional independence in the multivariable analysis (odds ratio 0.28 [0.109-0.722]; P = 0.008). CONCLUSIONS: Because functional independence can be achieved in the majority of high-grade aSAH survivors, aggressive initial management of high-grade aSAH is warranted. Strategies that reduce the need for permanent cerebrospinal fluid diversion may improve functional outcomes in survivors of high-grade aSAH.

Microsurgery Versus Stereotactic Radiosurgery for Brain Arteriovenous Malformations: A Matched Cohort Study.

BACKGROUND: Microsurgery (MS) and stereotactic radiosurgery (SRS) remain the preferred interventions for the curative treatment of brain arteriovenous malformations (AVM), but their relative efficacy remains incompletely defined. OBJECTIVE: To compare the outcomes of MS to SRS for AVMs through a retrospective, matched cohort study. METHODS: We evaluated institutional databases of AVM patients who underwent MS and SRS. MS-treated patients were matched, in a 1:1 ratio based on patient and AVM characteristics, to SRS-treated patients. Statistical analyses were performed to compare outcomes data between the 2 cohorts. The primary outcome was defined as AVM obliteration without a new permanent neurological deficit. RESULTS: The matched MS and SRS cohorts were each comprised of 59 patients. Both radiological (85 vs 11 mo; P < .001) and clinical (92 vs 12 mo; P < .001) follow-up were significantly longer for the SRS cohort. The primary outcome was achieved in 69% of each cohort. The MS cohort had a significantly higher obliteration rate (98% vs 72%; P = .001), but also had a significantly higher rate of new permanent deficit (31% vs 10%; P = .011). The posttreatment hemorrhage rate was significantly higher for the SRS cohort (10% for SRS vs 0% for MS; P = .027). In subgroup analyses of ruptured and unruptured AVMs, no significant differences between the primary outcomes were observed. CONCLUSION: For patients with comparable AVMs, MS and SRS afford similar rates of deficit-free obliteration. Nidal obliteration is more frequently achieved with MS, but this intervention also incurs a greater risk of new permanent neurological deficit.

SMART coils for intracranial aneurysm embolization: Follow-up outcomes.

The SMART coil (Penumbra Inc., Alameda, CA, USA) is a new microcoil designed to enhance deliverability. Although prior studies have described its perioperative safety and efficacy, the follow-up outcomes after embolization of intracranial aneurysms using SMART coils have not been reported. Therefore, the aim of this retrospective cohort study is to assess the angiographic outcomes at interim follow-up after aneurysm embolization with SMART coils. We reviewed data from consecutive patients with intracranial aneurysms who underwent endovascular treatment using SMART coils between June 2016 and August 2017. Baseline data and follow-up angiographic outcomes using the modified Raymond-Roy classification (MRRC) were recorded. The study cohort comprised 33 patients with 34 aneurysms who underwent SMART coil embolization and had sufficient follow-up data. The mean age was 57 years, and 82% were female. The mean aneurysm maximum diameter and neck width were 6.1 ±â€¯2.2 mm and 3.2 ±â€¯1.2 mm, respectively, and 14.7% of aneurysms were ruptured. The overall complication rate was 12%. Initial mean coil packing density was 26%, and the initial MRRC was I, II, IIIa, and IIIb in 24%, 26%, 35%, and 15%, respectively. At last follow-up (mean duration 7.7 ±â€¯3.2 months), the MRRC was I, II, IIIa, and IIIb in 62%, 26%, 3%, and 9%, respectively. The retreatment rate was 14.7%. The SMART coil is efficacious for the treatment of appropriately selected aneurysms, with an acceptable risk profile. The majority of residual aneurysms after the initial embolization procedure will progress to complete or near-complete occlusion at interim follow-up.

Effect of Dual Antiplatelet Therapy on Shunt Outcomes in Patients with Aneurysmal Subarachnoid Hemorrhage: A Matched Cohort Pilot Study.

OBJECTIVE: The aim of this retrospective, matched cohort study is to determine the effect of dual antiplatelet therapy (DAPT) on shunt-related complications and long-term functional outcomes in endovascularly treated aneurysmal subarachnoid hemorrhage (aSAH) patients. MATERIALS AND METHOD: We retrospectively analyzed an institutional database of aSAH patients from 2000-2015. Patients who underwent endovascular treatment with stent-assisted coiling (DAPT cohort) were matched in a 1:4 ratio to those who underwent coiling alone (no-DAPT cohort) based on the presenting patient and aneurysm factors. A favorable outcome was defined as a modified Rankin scale of <2. Statistical analyses were performed to compare the shunt-related and functional outcomes between the DAPT and no-DAPT cohorts. RESULTS: After applying the selection criteria and performing the matching process, the overall study cohort comprised 25 aSAH patients who underwent endovascular treatment, including five in the DAPT and 20 in the no-DAPT cohorts. The mean age, World Federation of Neurological Surgeons grade, aneurysm size, and follow-up duration of the overall study cohort were 52.3 years, 2.9, 7.4 mm, and 32.7 months, respectively. The mean time from aSAH to shunt placement was significantly higher for patients in the DAPT cohort (5.6 vs. 0.7 months; p=0.026). The shunt complication rates (p=0.562) and functional outcomes at last follow-up (p=0.924) were not significantly different between the two cohorts. CONCLUSION: Patients receiving DAPT after the stent-assisted coiling of acutely ruptured aneurysms do not have an increased risk of shunt-related complications or unfavorable long-term functional outcomes compared to endovascularly treated aSAH patients not taking DAPT. These results suggest that further study is warranted.

Endoport-assisted surgical evacuation of a deep-seated cerebral abscess.

Conventional surgical treatment for cerebral abscesses includes craniotomy or stereotactic aspiration. Deep-seated, large abscesses pose a challenge to neurosurgeons, due to the risk of injury to the cortex and white matter tracts secondary to the brain retraction necessary to access the lesion. The endoport is a tubular conduit that can be employed for minimally invasive approaches to deep-seated intracranial lesions, and it may reduce the length of dural opening, size of corticotomy, and retraction-related injury. In this technical note, we present the first report of an adult with a deep cerebral abscess which was successfully treated with endoport-assisted surgical evacuation. The endoport has been shown to be useful for the treatment of other intracranial pathologies, and we believe that this technology may be employed for the evacuation of appropriately selected cerebral abscesses.

Sylvian Arteriovenous Malformation Resection and Associated Middle Cerebral Artery Aneurysm Clipping: Technical Nuances of Concurrent Surgical Treatment.

Approximately 10-30% of brain arteriovenous malformations (AVM) have associated arterial aneurysms (AAA), and the management of these lesions can be challenging. In this video technical note, we demonstrate the microsurgical treatment of an unruptured, Spetzler-Martin grade I AVM in the distal Sylvian fissure with two AAAs arising proximally from the inferior M2 trunk immediately distal to the middle cerebral artery (MCA) bifurcation. First, we resected the superficially located AVM to normalize the blood flow through the Sylvian vein. Next, we performed a Sylvian fissure dissection to access and clip the two MCA AAAs. We also discuss the technical nuances of tandem surgical intervention for AVMs with AAAs as it pertains to this case, particularly with respect to the order of lesion treatment, Sylvian fissure dissection, nidal resection, and aneurysm clipping.

Outcomes After Off-Label Use of the Pipeline Embolization Device for Intracranial Aneurysms: A Multicenter Cohort Study.

OBJECTIVE: To examine outcomes of Pipeline embolization device (PED) use for treatment of intracranial aneurysms outside of U.S. Food and Drug Administration-approved indications. METHODS: Data from patients with aneurysms treated with off-label use of PED were pooled from 4 centers in a retrospective multicenter cohort study. Primary endpoints were decline in modified Rankin Scale score by at least 1 point and angiographic aneurysm occlusion at follow-up. RESULTS: The study cohort comprised 109 patients. Mean aneurysm size was 8.4 ± 7.4 mm, 20.2% of aneurysms were located in the posterior circulation, and 11.9% of aneurysms were ruptured. The most common reasons for off-label use were aneurysm size (50.5%), aneurysm location (25.7%), and both size and location (10.1%). Mean follow-up was 9 months. Complete occlusion was achieved in 82.5% of cases at last angiographic follow-up. Modified Rankin Scale score decline was found in 18.8% of cases. On univariate analysis, age, aneurysm size, aneurysm morphology, aneurysm location, reason for off-label use, and rupture status were not associated with clinical decline or aneurysm occlusion on angiography. On multivariate analysis, treatment of a ruptured aneurysm with PED was found to be an independent predictor of postoperative decline in modified Rankin Scale score, and size as the only reason for off-label PED use was found to be an independent predictor of complete occlusion on final angiography. CONCLUSIONS: Off-label use of PED has a reasonable risk-to-benefit profile for appropriately selected aneurysms. Posterior circulation location and fusiform morphology do not appear to be associated with worse clinical or angiographic outcomes.

Development of an Intracranial Dural Arteriovenous Fistula after Venous Sinus Stenting for Idiopathic Intracranial Hypertension.

We report a case in which an intracranial dural arteriovenous fistula (DAVF) developed after endovascular treatment of a patient with idiopathic intracranial hypertension with venous sinus stenting (VSS). The pathogenesis may involve hemodynamic alterations secondary to increased poststenting venous sinus pressure, which may cause new arterial ingrowth into the fistulous sinus wall without capillary interposition. Despite administration of dual antiplatelet therapy, there may also be subclinical cortical vein thrombosis that contributed to DAVF formation. In addition to the aforementioned mechanisms, increased inflammation induced by VSS may upregulate vascular endothelial growth factor and platelet-derived growth factor expression and also promote DAVF pathogenesis. Since VSS has been used to obliterate DAVFs, DAVF formation after VSS may seem counterintuitive. Previous stents have generally been closed cell, stainless steel designs used to maximize radial compression of the fistulous sinus wall. In contrast, our patient's stent was an open cell, self-expandable nitinol design (Protégé Everflex). Neurointerventionalists should be aware of this potential, although rare complication of DAVF formation after VSS.

Posterior circulation perforator aneurysms: a proposed management algorithm.

INTRODUCTION: Subarachnoid hemorrhage (SAH) from posterior circulation perforator aneurysms (PCPAs) is rare and its natural history is unknown. Diagnosis may be difficult, acute management is poorly defined, and long-term recurrent SAH rates and clinical outcome data are lacking. METHODS: We searched our institution's records for cases of PCPA rupture and analyzed patient demographics, Hunt and Hess (HH) grades, diagnostic imaging, management, and clinical outcomes. We conducted telephone interviews to calculate modified Rankin Scale (mRS) scores. RESULTS: We identified 9 patients (6 male, 3 female) with a ruptured PCPA who presented to the University of Virginia Health System (Charlottesville, VA, USA) between 2010 and 2016. Median and mean ages were 62 and 63 years, respectively. Median HH grade was 3. Seven of nine (78%) PCPAs were angiographically occult on initial imaging and median time to diagnosis was 5 days. Three conservatively managed patients had a mean mRS score of 0.67 (range 0-1) at mean follow-up of 35.3 months. Antifibrinolytic therapy was administered to all conservatively managed patients without thrombotic complication. Six patients receiving endovascular treatment had a mean mRS score of 2.67 (range 0-6) at mean follow-up of 49.2 months. No cases of recurrent SAH were seen in the study. CONCLUSIONS: The rarity of PCPA has precluded long-term clinical follow-up until now. Our experience suggests low recurrent SAH rates. Until further studies are performed, conservative management, possibly combined with antifibrinolytic therapy, may be a viable treatment with acceptable long-term outcome.

Transient resolution of venous sinus stenosis after high-volume lumbar puncture in a patient with idiopathic intracranial hypertension.

Stenosis of the transverse sinus (TS) and sigmoid sinus (SS), with a trans-stenosis pressure gradient, has been implicated in the pathophysiology of idiopathic intracranial hypertension (IIH). MRI has shown improvement in TS and SS stenosis after high-volume lumbar puncture (HVLP) in a subset of patients with IIH. The authors present the first report of an IIH patient with immediate post-HVLP TS and SS trans-stenosis pressure gradient reduction and an attendant increase in TS and SS cross-sectional area confirmed using intravascular ultrasonography (IVUS). Recurrence of the patient's TS-SS stenosis coincided with elevated HVLP opening pressure, and venous sinus stent placement resulted in clinical improvement. This report suggests that TS and SS stenosis may be a downstream effect of elevated intracranial pressure in IIH, rather than its principal etiological mechanism. However, the authors hypothesize that endovascular stenting may obliterate a positive feedback loop involving trans-stenosis pressure gradients, and still benefit appropriately selected patients.

SMART coils for intracranial aneurysm embolization: Initial outcomes.

OBJECTIVES: Endovascular technology for the treatment of intracranial aneurysms continues to rapidly evolve. The SMART coil (Penumbra Inc., Alameda, CA, USA) is a novel microcoil designed to enhance deliverability. The aim of this single-center, retrospective cohort study is to assess the initial outcomes after aneurysm embolization using SMART coils. PATIENTS AND METHODS: We reviewed consecutive patients with intracranial aneurysms who underwent endovascular embolization using SMART coils from June 2016 to January 2017. Baseline and initial outcomes data were analyzed. RESULTS: The study cohort was comprised of 32 patients with 33 aneurysms. The mean age was 55.8 years. The majority (85%) of aneurysms were located in the anterior circulation. The mean aneurysm maximum diameter and neck width were 6.0mm and 3.1mm, respectively. Dome irregularity and fusiform aneurysm morphology were noted in 33% and 9% of aneurysms, respectively, and 15% presented with subarachnoid hemorrhage. No serious procedural complications occurred, including microcatheter prolapse, intraprocedural aneurysm rupture, or thromboembolism. Device malfunction occurred in one case (3%). The mean packing density was 25%, and the degree of immediate post-embolization aneurysm occlusion was a modified Raymond-Roy grade I, II, IIIa, and IIIb in 48%, 27%, 18%, and 6%, respectively. CONCLUSION: Our preliminary findings suggest that the SMART coil has a favorable initial risk to benefit profile for the embolization of appropriately selected aneurysms. Additional studies of larger cohorts are necessary to determine the mid-term and long-term clinical and angiographic outcomes of aneurysm patients treated with the SMART coil.

Delayed cyst formation after stereotactic radiosurgery for brain arteriovenous malformations.

OBJECTIVE: Stereotactic radiosurgery (SRS) is a commonly employed treatment modality for brain arteriovenous malformations (AVMs). However, due to the low frequency of delayed cyst formation after AVM SRS, as well as the prolonged time interval between treatment and its occurrence, the characteristics of post-SRS cyst formation are not well defined. Therefore, the aims of this retrospective cohort study are to determine the rate of cyst formation after SRS for AVMs, identify predictive factors, and evaluate the clinical sequelae of post-SRS cysts. METHODS: The authors analyzed an SRS database for AVM patients who underwent SRS at the University of Virginia and identified those who developed post-SRS cysts. Statistical analyses were performed to determine predictors of post-SRS cyst formation and the effect of cyst formation on new or worsening seizures after SRS. RESULTS: The study cohort comprised 1159 AVM patients treated with SRS; cyst formation occurred in 17 patients (post-SRS cyst rate of 1.5%). Compared with patients who did not develop post-SRS cysts, those with cyst formation were treated with a greater number of radiosurgical isocenters (mean 3.8 vs 2.8, p = 0.047), had a longer follow-up (mean 132 vs 71 months, p < 0.001), were more likely to develop radiological radiation-induced changes (RIC) (64.7% vs 36.1%, p = 0.021), and had a longer duration of RIC (57 vs 21 months, p < 0.001). A higher number of isocenters (p = 0.014), radiological RIC (p = 0.002), and longer follow-up (p = 0.034) were found to be independent predictors of post-SRS cyst formation in the multivariate analysis. There was a trend toward a significant association between cyst formation and new or worsening seizures in univariate analysis (p = 0.054). CONCLUSIONS: Patients with greater nidal complexity appear to be more prone to post-SRS cyst formation. The findings of this study emphasize the importance of long-term follow-up for patients who have undergone AVM SRS, even after nidal obliteration is achieved. Post-SRS cysts may be epileptogenic, although seizure outcomes after AVM SRS are multifactorial.