Stereotactic radiosurgery (SRS) for vestibular schwannomas has evolved and improved over time. Although early short-term follow-up reports suggest that fractionation yields hearing preservation rates equivalent to modern single-dose SRS techniques, significant questions remain regarding long-term tumor control after the use of fractionation in a late responding tumor with a low proliferative index and α/β ratio. With single-dose SRS, critical hearing preservation variables include: 1) strict attention to prescription dose 3D conformality so that the ventral cochlear nucleus (VCN) receives ≤ 9 Gy; 2) careful delineation of the 3D tumor margin to exclude the cochlear nerve when visualizable with contrast-enhanced T2-weighted MR volumetric imaging techniques and exclusion the dura mater of the anterior border of the internal auditory canal; 3) a tumor margin dose prescription ≤ 12 Gy; 4) optimization of the tumor treatment gradient index without sacrificing coverage and conformality; and 5) strict attention to prescription dose 3D conformality so that the modiolus and the basal turn of the cochlea receive the lowest possible dose (ideally < 4–5.33 Gy). Testable correlates for the relative importance of the VCN versus cochlear dose given the tonotopic organization of each structure suggests that VCN toxicity should lead to preferential loss of low hearing frequencies, while cochlear toxicity should lead to preferential loss of high hearing frequencies. The potential after SRS for hearing toxicity from altered endolymph and/or perilymph fluid dynamics either via impaired fluid production and/or absorption has yet to be explored. Serous otitis media, ossicular or temporal bone osteonecrosis, and chondromalacia are not likely to be relevant factors or considerations for hearing preservation after SRS.
Mark E. Linskey
✓ By definition, the term “radiosurgery” refers to the delivery of a therapeutic radiation dose in a single fraction, not simply the use of stereotaxy. Multiple-fraction delivery is better termed “stereotactic radiotherapy.” There are compelling radiobiological principles supporting the biological superiority of single-fraction radiation for achieving an optimal therapeutic response for the slowly proliferating, late-responding, tissue of a schwannoma. It is axiomatic that complication avoidance requires precise three-dimensional conformality between treatment and tumor volumes. This degree of conformality can only be achieved through complex multiisocenter planning. Alternative radiosurgery devices are generally limited to delivering one to four isocenters in a single treatment session. Although they can reproduce dose plans similar in conformality to early gamma knife dose plans by using a similar number of isocenters, they cannot reproduce the conformality of modern gamma knife plans based on magnetic resonance image—targeted localization and five to 30 isocenters.
A disturbing trend is developing in which institutions without nongamma knife radiosurgery (GKS) centers are championing and/or shifting to hypofractionated stereotactic radiotherapy for vestibular schwannomas. This trend appears to be driven by a desire to reduce complication rates to compete with modern GKS results by using complex multiisocenter planning. Aggressive advertising and marketing from some of these centers even paradoxically suggests biological superiority of hypofractionation approaches over single-dose radiosurgery for vestibular schwannomas. At the same time these centers continue to use the term radiosurgery to describe their hypofractionated radiotherapy approach in an apparent effort to benefit from a GKS “halo effect.” It must be reemphasized that as neurosurgeons our primary duty is to achieve permanent tumor control for our patients and not to eliminate complications at the expense of potential late recurrence. The answer to minimizing complications while maintaining maximum tumor control is improved conformality of radiosurgery dose planning and not resorting to homeopathic radiosurgery doses or hypofractionation radiotherapy schemes.
Mark E. Linskey, Hae Dong Jho and Peter J. Jannetta
✓ Thirty-one (2%) of 1404 consecutive patients with typical trigeminal neuralgia who underwent microvascular decompression between 1972 and 1993 were found to have vascular compression by the vertebral artery (VA) or the basilar artery (BA). Compared to the remaining 1373 patients, this subgroup was older (mean age 62 vs. 55 years, p < 0.001), was predominantly male (68% vs. 39%, p < 0.002), demonstrated left-sided predominance (65% vs. 39%, p < 0.002), was more likely to be hypertensive (65% vs. 18%, p < 0.001), and was more likely to have ipsilateral hemifacial spasm (16% vs. 0.6%, p < 0.001). The trigeminal nerve was compressed by the VA in 18 cases (the VA alone in three and the VA plus other vessels in 15), the BA in 12 cases (the BA alone in four and the BA plus other vessels in eight), and the vertebrobasilar junction in one case. Twenty-nine of the 31 patients underwent vascular decompression of the trigeminal nerve, one had a complete trigeminal root section, and one underwent partial root section with vascular decompression of the remaining nerve.
All 31 patients were pain-free, off medication immediately after surgery, and this pain-free, medication-free status was maintained at 1 year after surgery in 96% of cases, at 3 years in 92%, and at 10 years in 86%, based on life-table analysis. Minor trigeminal hypesthesia/hypalgesia was present preoperatively in 52%. New or worsened minor hypesthesia/hypalgesia developed in 41% of patients, while transient diplopia as well as hearing loss developed in 23% and 13% in the overall series, respectively. No patient developed major trigeminal sensory loss or masseter weakness after vascular decompression alone. There was no operative mortality. Vascular decompression is an effective treatment for patients with trigeminal neuralgia who have vertebrobasilar compression of the trigeminal nerve. Patients should be warned that decompression of a tortuous vertebrobasilar system carries a higher risk of mild trigeminal dysfunction, diplopia, and hearing loss than standard microvascular decompression.
Mark E. Linskey, Laligam N. Sekhar and Stephen T. Hecht
✓ Balloon test occlusion of the internal carotid artery (ICA) is useful in preoperatively assessing the risk of temporary occlusion or permanent sacrifice of the carotid artery. The incidence of symptomatic complications from this procedure is 1.7%. The case is reported of a 57-year-old woman in whom a balloon test occlusion of the left ICA was attempted. She developed a left ICA dissection/occlusion with subsequent embolization to the left middle cerebral artery, leading to right-sided hemiplegia and expressive aphasia. She was successfully treated by an emergency embolectomy followed by surgical repair of the left ICA, with an excellent outcome. This case represents the most serious complication encountered by the authors in more than 300 balloon test occlusions. Means of avoiding this complication during balloon test occlusion as well as the important factors in managing this problem are emphasized.
Mark E. Linskey, Peter J. Jannetta and A. Julio Martinez
✓ A patient with an enhancing, completely intracanalicular mass on magnetic resonance imaging was operated on for a presumed acoustic neurilemoma, but was found at surgery to have an intracanalicular vascular malformation. This rare lesion should be distinguished from angiomatous change within an acoustic neurilemoma and in the past has been termed “vascular tumor,” “hemangioma,” or “fibro-angioma.” The clinical distinctions between intracanalicular acoustic neurilemomas and intracanalicular vascular malformations and the ability of magnetic resonance imaging to distinguish between the two are discussed.
Mark E. Linskey, Stephen A. Davis and Vaneerat Ratanatharathorn
Object. The authors sought to assess the respective roles of microsurgery and gamma knife surgery (GKS) in the treatment of patients with meningiomas.
Methods. The authors culled from a 4-year prospective database data on 74 cases of meningiomas. Thirty-eight were treated with GKS and 35 with microsurgery. Simpson Grade 1 or 2 resection was achieved in 86.1% of patients who underwent microsurgery. Patients who underwent GKS received a mean margin dose of 16.4 Gy (range 14–20 Gy). The mean tumor coverage was 94.7%, and the mean conformity index was 1.76. Significant differences between the two treatment groups (GKS compared with microsurgery) included age (mean 60 compared with 50.7 years), volume (mean 7.85 cm3 compared with 44.4 cm3), treatment history (55.3% compared with 14.3%), and tumor location (cavernous sinus/petroclival, 14 compared with three). The median follow up was 21.5 months (range 1.5–50 months). In patients with benign meningiomas GKS tumor control was 96.8% with one recurrence at the margin. The recurrence rate was zero of 27 for Simpson Grade 1 or 2 resection and three of four for higher grades in those patients who underwent microsurgery. There was no procedure-related mortality or permanent major neurological morbidity. The mean Karnofsky Performance Scale score was maintained for both forms of treatment. Symptoms improved in 48.4% of patients undergoing microsurgery and 16.7% of those who underwent GKS. Transient and permanent cranial nerve morbidity was 7.9 compared with 2.9%, and 5.3 compared with 8.5% for GKS and microsurgery, respectively. In a patient satisfaction survey 93.1% of microsurgery patients and 91.2% of GKS patients were highly satisfied.
Conclusions. Both GKS and microsurgery serve important roles in the overall management of patients with meningiomas. Both are safe and effective and provide high degrees of satisfaction when used for differentially selected patients.
Marlon S. Mathews, Mark E. Linskey and Devin K. Binder
✓ As a trainee of Dr. Harvey Cushing, cofounder and first president of the American Association of Neurological Surgeons, and founder of a prestigious international academic fellowship, Dr. William P. van Wagenen is an important figure in the history of neurological surgery. Perhaps less well known or appreciated is his seminal role as the first neurosurgeon to attempt, study, and publish results of the corpus callosotomy procedure for patients with epilepsy, and his collaboration with Andrew J. Akelaitis, which led to the description of some features of “split-brain” patients 2 decades before similar work in the 1960s eventually resulted in a Nobel Prize for Roger W. Sperry in 1981. These contributions firmly establish William P. van Wagenen as one of the founding pioneers in the surgical treatment of patients with epilepsy.
Mark E. Linskey, Vaneerat Ratanatharathorn and Jose Peñagaricano
The aim of this study was to analyze 1 surgeon's 4-year experience with microvascular decompression ([MVD], 36 patients) and Gamma Knife surgery ([GKS], 44 patients) in 80 consecutive patients with trigeminal neuralgia (TN).
The authors conducted a prospective cohort study from March 1999 to December 2003 with an independent clinical assessment of the results and serial patient satisfaction surveys. All patients completed a 2004 patient satisfaction survey (0.5–5 years postoperative), and 70% of surviving patients completed the same survey in 2007 (3.9–8.5 years postoperative). Follow-up was undertaken in 100% of the patients (mean 3.4 ± 2.14 years, range 0.17–8.5 years).
Respective initial and latest follow-up raw pain-free rates were 100 and 80.6% for MVD and 77.3 and 45.5% for GKS. The median time to the maximal benefit after GKS was 4 weeks (range 1 week–6 months). Respective initial, 2-, and 5-year actuarial pain-free rates were 100, 88, and 80% for MVD and 78, 50, and 33% for GKS (p = 0.0002). The relative risk of losing a pain-free status by 5 years posttreatment was 3.35 for patients in the GKS group compared with the MVD group. Initial and 5-year actuarial rates for ≥ 50% pain relief after GKS were 100 and 80%, respectively. The respective rates of permanent mild and severe sensory loss were 5.6 and 0% for patients in the MVD group, as opposed to 6.8 and 2.3% for patients in the GKS group. Anesthesia dolorosa did not occur during the study. Both procedures enjoyed a high degree of early patient satisfaction (95–100%). Microvascular decompression maintained the same rate of patient satisfaction, but satisfaction with GKS decreased to 75% as pain control waned. Twenty-three patients (29%) died of causes unrelated to the TN or the surgical intervention during the follow-up, and their pain status was known at the time of death. Statistically significant intergroup differences for the MVD versus GKS cohorts were age (median 54 years, range 36–70 years vs median 74 years, range 48–92 years, respectively), preoperative symptom duration (median 2.58 years, range 0.33–15 years vs median 7.5, range 0.6–40 years, respectively), and the presence of major comorbidities (2.8 vs 58.3%, respectively).
In this nonrandomized prospective cohort trial of selected patients with potentially relevant intergroup differences, MVD was significantly superior to GKS in achieving and maintaining a pain-free status in those with TN and provided similar early and superior longer-term patient satisfaction rates compared with those for GKS. The complications of wound cerebrospinal fluid leakage, hearing loss, and persistent diplopia (1 case each in the MVD group) were not seen after GKS.
Mark E. Linskey, Peter A. S. Johnstone, Michael O'Leary and Steven Goetsch
Object. The dosimetry of radiation exposure of healthy inner, middle, and external ear structures that leads to hearing loss, tinnitus, facial weakness, dizziness, vertigo, and imbalance after gamma knife surgery (GKS) for vestibular schwannomas (VSs) is unknown. The authors quantified the dose of radiation received by these structures after GKS for VS to assess the likelihood that these doses contributed to postradiosurgery complications.
Methods. A retrospective study was performed using a prospectively acquired database of a consecutive series of 54 patients with VS who were treated with GKS during a 3.5-year period at an “open unit” gamma knife center. Point doses were measured for 18 healthy temporal bone structures in each patient, with the anatomical position of each sampling point confirmed by a fellowship-trained neurootologist. These values were compared against single-dose equivalents for the 5-year tolerance dose for a 5% risk of complications and the 5-year tolerance dose for a 50% risk of complications, which were calculated using known 2-Gy/fraction thresholds for chronic otitis, chondromalacia, and osseous necrosis, as well as the tumor margin dose and typical tumor margin prescription doses for patients in whom hearing preservation was attempted.
External and middle ear doses were uniformly low. The intratemporal facial nerve is susceptible to unintentionally high radiation exposure at the fundus of the internal auditory canal, with higher than tumor margin doses detected in 26% of cases. In the cochlea, the basal turn near the modiolus and its inferior portion are most susceptible, with doses greater than 12 Gy detected in 10.8 and 14.8% of cases. In the vestibular labyrinth, the ampulated ends of the lateral and posterior semicircular canals are most susceptible, with doses greater than 12 Gy detected in 7.4 and 5.1% of cases.
Conclusions. Doses delivered to middle and external ear structures are unlikely to contribute to post-GKS complications, but unexpectedly high doses may be delivered to sensitive areas of the intratemporal facial nerve and inner ear. Unintentional delivery of high doses to the stria vascularis, the sensory neuroepithelium of the inner ear organs and/or their ganglia, may play a role in the development of post-GKS tinnitus, hearing loss, dizziness, vertigo, and imbalance. Minimizing treatment complications post-GKS for VS requires precise dose planning conformality with the three-dimensional surface of the tumor.