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Michael J. Link, Douglas Kondziolka and Madjid Samii

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Theresa M. Cheng, Michael J. Link and Burton M. Onofrio

✓ Extreme lateral disc herniations are increasingly recognized as a cause of lumbar nerve root compression syndromes. This disorder often presents major diagnostic and therapeutic challenges, especially in the presence of multiple degenerative changes and chronic back pain in elderly patients. The authors describe two patients with presentations and findings that have not been previously described in the literature. Both patients had histories of upper lumbar back and leg pain. Degenerative spine disease, gaseous degeneration of the intervertebral discs, and epidural gas in the lateral recesses were noted on imaging studies. However, because both patients had undergone prior epidural diagnostic and therapeutic procedures, the epidural gas in the lateral recesses could be attributed either to gaseous disc degeneration or to the previous intraspinal procedures. One patient was found to have a large, far lateral extruded disc fragment that contained air. The nerve root in the second patient was impaled by an unusual combination of a small extruded disc fragment as well as an air-filled sac that was surrounded by the walled-off fragment's capsule and which freely communicated with the gaseous degenerated disc space. The suspected mechanism of root compression is illustrated and discussed. The possibility of disc herniation should be seriously considered in cases of nerve root compression in which epidural gas is present, especially those associated with gaseous degenerated discs.

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Ganglioglioma in the cerebellopontine angle in a child

Case report and review of the literature

Brian D. Milligan, Caterina Giannini and Michael J. Link

✓The authors report a case of a posterior fossa ganglioglioma centered in the cerebellopontine angle occurring in a child. As with cortically based gangliogliomas, the primary therapy is resection. When the tumor presents in the posterior fossa, often only partial resection can be accomplished without significant neurological deficit. The role of adjuvant chemotherapy and radiation therapy remains controversial, although these are usually reserved for high-grade lesions or progressive growth. The literature regarding the natural history, surgical outcomes, and indications for adjuvant therapy is reviewed. Although it occurs rarely, ganglioglioma should be included in the differential diagnosis of a posterior fossa mass in a child or young adult.

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Jean Régis, Christine Delsanti and Pierre-Hugues Roche

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Bruce E. Pollock, Michael J. Link and Robert L. Foote

Object

The decline in cranial nerve morbidity after radiosurgery for vestibular schwannoma (VS) correlates with dose reduction and other technical changes to this procedure. The effect these changes have had on tumor control has not been well documented.

Methods

The authors performed a retrospective review of 293 patients with VSs who underwent radiosurgery between 1990 and 2004 and had a minimum of 24 months of imaging follow-up (90% of the entire series). The median radiation dose to the tumor margin was 13 Gy. Treatment failure was defined as progressive tumor enlargement noted on 2 or more imaging studies. The mean postradiosurgical follow-up was 60.9 ± 32.5 months.

Results

Tumor growth was noted in 15 patients (5%) at a median of 32 months after radiosurgery. Radiographically demonstrated tumor control was 96% at 3 years and 94% at 7 years after radiosurgery. Univariate analysis revealed 2 factors that correlated with failed radiosurgery for VS: an increasing number of isocenters (p = 0.03) and tumor margin radiation doses ≤ 13 Gy (p = 0.02). Multivariate analysis showed that only an increasing number of isocenters correlated with failed VS radiosurgery (hazard ratio 1.1, 95% CI 1.02–1.32, p < 0.05). The tumor margin radiation dose (p = 0.22) was not associated with tumor growth after radiosurgery.

Conclusions

Distortion of stereotactic MR imaging coupled with increased radiosurgical conformality and progressive dose reduction likely caused some VSs to receive less than the prescribed radiation dose to the entire tumor volume.

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Todd A. Patrick, Caterina Giannini, Michael J. Ebersold and Michael J. Link

✓ Metastatic seeding or iatrogenic implantation of numerous types of primary central nervous system tumors, typically along cerebrospinal fluid pathways, is a frequently described albeit rare phenomenon and has never been reported in association with vestibular schwannoma (VS). The authors present a case of inadvertent surgical implantation of VS into the cerebellar hemisphere during resection of a recurrent VS in the cerebellopontine angle and internal auditory canal. A 42-year-old man presented with a 2.5-cm right VS that was removed without complication via a retrosigmoid approach. Routine imaging performed 5 years later revealed a 1.5-cm recurrence of the VS that was subsequently removed by reopening the retrosigmoid craniotomy. Five years later—10 years after initial presentation—follow-up imaging revealed a 1-cm recurrence of the VS and a separate 2.2-cm tumor in the inferior cerebellar parenchyma with surrounding edema. Both tumors were removed without complication by reopening the previous retrosigmoid craniotomy. Histological evaluation of these tumors revealed features typical of VS and similar to those of the tissue obtained from the two prior resections. Given the similarities among these tumors in pathological appearance and mitotic index, the presence of the intraparenchymal cerebellar schwannoma was probably due to intraoperative iatrogenic implantation.

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Michael J. Link, Robert J. Coffey, Douglas A. Nichols and Deborah A. Gorman

✓ Over the past 5 years 29 patients with dural arteriovenous fistulas (AVFs) were treated by the authors using the Leksell radiosurgical gamma knife unit. Within 2 days after radiosurgery, 17 patients with AVFs that exhibited retrograde pial or cortical venous drainage (12 patients) and/or produced intractable bruit (eight patients) underwent particulate embolization of external carotid feeding vessels. The rationale for this treatment strategy was that radiosurgery was expected to cause obliteration of most fistulas after 12 to 36 months. In patients with bruit, ocular symptoms, or in those at risk for hemorrhage, treatment with embolization after radiosurgery kept the fistulas angiographically visible for radiosurgical targeting yet offered palliation of symptoms and temporary, partial protection from hemorrhage during the latency period. In 12 patients, preobliteration embolization immediately reduced (10 patients) or eliminated (two patients) retrograde pial venous drainage. To date, no lesion has hemorrhaged after treatment. Angiography 1 to 3 years posttreatment in 18 patients showed total obliteration of 13 fistulas (72%) and partial obliteration of five (28%). Radiosurgery, followed by embolization when retrograde pial venous drainage, intractable bruit, and/or major external carotid artery supply is present, appears to be a promising treatment for selected patients with symptomatic dural AVFs.

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Kelly D. Flemming, Michael J. Link, Teresa J. H. Christianson and Robert D. Brown Jr.

Object

The goal of this study was to determine the risk of using antithrombotic agents in patients with established intracerebral cavernous malformations (ICMs).

Methods

From a previously described cohort of 292 patients with radiographically defined ICMs, 40 required an antithrombotic after the ICM was diagnosed. Patients underwent follow-up to determine the incidence of hemorrhage.

Results

The mean age of these 40 patients was 62.4 years; there were 21 male and 19 female patients. Five (12.5%) of the 40 patients initially presented with hemorrhage and 4 (10%) had multiple ICMs. Of these patients, 32 were placed on an antiplatelet agent alone, 6 on an anticoagulant alone, and 2 were placed on both. In patients necessitating any antithrombotic agent, 1 patient developed a prospective hemorrhage over the 258 person-years of follow-up (prospective hemorrhage rate 0.41% per person-year).

Conclusions

Antithrombotics likely do not precipitate hemorrhage in patients with known ICMs. However, caution should be exercised in the use of antithrombotics in patients with ICMs at high risk for hemorrhage. The risks and benefits of antithrombotics in each situation should be carefully weighed against the natural history of ICM.

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Jonathan M. Bledsoe, Michael J. Link, Scott L. Stafford, Paul J. Park and Bruce E. Pollock

Object

Stereotactic radiosurgery (SRS) has proven to be a safe and effective treatment for many patients with intracranial meningiomas. Nevertheless, the morbidity associated with radiosurgery of larger meningiomas is poorly understood.

Methods

The authors performed a retrospective review of 116 patients who underwent SRS for meningiomas (WHO Grade I) > 10 cm3 between 1990 and 2007, with a minimum follow-up of 12 months. Patients with atypical or malignant meningiomas and those who received prior radiotherapy were excluded. The average tumor volume was 17.5 cm3 (range 10.1–48.6 cm3); the average tumor margin dose was 15.1 Gy (range 12–18 Gy); and the mean follow-up duration was 70.1 months (range 12–199 months).

Results

Tumor control was 99% at 3 years and 92% at 7 years after radiosurgery. Thirty complications after radiosurgery were noted in 27 patients (23%), including 7 cases of seizures, 6 cases of hemiparesis, 5 cases of trigeminal injury, 4 cases of headaches, 3 cases of diplopia, 2 cases each of cerebral infarction and ataxia, and 1 case of hearing loss. Patients with supratentorial tumors experienced a higher complication rate compared with patients with skull base tumors (44% compared with 18%) (hazard ratio 2.9, 95% CI 1.3–6.7, p = 0.01).

Conclusions

The morbidity associated with SRS for patients with benign meningiomas > 10 cm3 is greater for supratentorial tumors compared with skull base tumors. Whereas radiosurgery is relatively safe for patients with large-volume skull base meningiomas, resection should remain the primary disease management for the majority of patients with large-volume supratentorial meningiomas.

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Cormac O. Maher, Robert E. Anderson, Robyn L. McClelland and Michael J. Link

Object. The authors evaluated a new non—cross-linked, propylene oxide—treated, acellular collagen matrix for use as a dural substitute in rabbits. They then compared this material to a commonly used dural substitute as well as to native dura mater used during primary closure.

Methods. Forty-six rabbits were randomly assigned to eight groups of five or six rabbits each. These groups differed according to the type of closure material that was used during surgery (native dura, control dural substitute, or experimental dural substitute) and the duration of convalescence. At the end of the experiment, the tightness of the duraplasty was assessed in each live rabbit by continuous infusion of fluid into the cisterna magna until leakage was detected. The animals were killed and each specimen was sectioned and studied histologically. The authors found that the experimental dural substitute was safe in animals for this application, that it held sutures well, and that a watertight closure was usually achieved. There were fewer adhesions between the experimental material and neural tissue was less likely to adhere to the cranium than the control graft. Histological examination showed that the experimental material had slightly more spindle cells and vascularity than the control graft.

Conclusions. The experimental graft material has several features that make it an attractive candidate for use as a dural substitute.