Faculty Bibliography

OBJECTIVE: The obliteration response of an arteriovenous malformation (AVM) to radiosurgery is strongly dependent on dose and volume. For larger volumes, the dose must be reduced for safety, but this compromises obliteration. In 1992, we prospectively began to stage anatomic components in order to deliver higher single doses to symptomatic AVMs > 15 ml in volume. METHODS: During a 17-year interval at the University of Pittsburgh, 1040 patients underwent radiosurgery for a brain AVM. Out of 135 patients who had multiple procedures, 37 patients underwent prospectively staged volume radiosurgery for symptomatic otherwise unmanageable larger malformations. Twenty-eight patients who were managed before 2002 were included in this study to achieve sufficient follow-up in assessing the outcomes. The median age was 37 years (range, 13-57 yr). Thirteen patients had previous hemorrhages and 13 patients had attempted embolization. Separate anatomic volumes were irradiated at 3 to 8 months (median, 5 mo) intervals. The median initial AVM volume was 24.9 ml (range, 10.2-57.7 ml). Twenty-six patients had two stages and two had three-stage radiosurgery. Seven patients had repeat radiosurgery after a median interval of 63 months. The median target volume was 12.3 ml. (range, 4.2-20.8 ml.) at Stage I and 11.5 ml. (range, 2.8-22 ml.) at Stage II. The median margin dose was 16 Gy at both stages. Median follow-up after the last stage of radiosurgery was 50 months (range, 3-159 mo). RESULTS: Four patients (14%) sustained a hemorrhage after radiosurgery; two died and two patients recovered with mild permanent neurological deficits. Worsened neurological deficits developed in one patient. Seizure control was improved in three patients, was stable in eight patients and worsened in two. Magnetic resonance imaging showed T2 prolongation in four patients (14%). Out of 28 patients, 21 had follow-up more than 36 months. Out of 21 patients, seven underwent repeat radiosurgery and none of them had enough follow- up. Of 14 patients followed for more than 36 months, seven (50%) had total, four (29%) near total, and three (21%) had moderate AVM obliteration. CONCLUSIONS: Prospective staged volume radiosurgery provided imaging defined volumetric reduction or closure in a series of large AVMs unsuitable for any other therapy. After 5 years, this early experience suggests that AVM related symptoms can be stabilized and anticipated bleed rates can be reduced.

OBJECT: The aim of this paper was to determine prognostic factors for adult medulloblastoma treated with boost Gamma Knife surgery (GKS) following resection and craniospinal irradiation. METHODS: The authors performed a retrospective analysis of 12 adult patients with histologically proven medulloblastoma or supratentorial primitive neuroectodermal tumor who between February 1991 and December 2004 underwent >or=1 sessions of GKS for posttreatment residual or recurrent tumors (6 tumors in each group). Before GKS, all patients had undergone a maximal feasible resection followed by craniospinal irradiation. Nine patients also received systemic chemotherapy. Stereotactic radiosurgery was applied to residual and recurrent posterior fossa tumor as well as to foci of intracranial medulloblastoma metastases. The median time interval from initial diagnosis and resection to the first GKS treatment was 24 months (range 2-37 months). The mean GKS-treated tumor volume was 9.4 cm3 (range 0.5-39 cm3). RESULTS: Following adjunctive radiosurgery, 5 patients had no evidence of tumor on magnetic resonance (MR) imaging, 3 patients had stable tumor burden on MR imaging, and 4 patients had evidence of tumor progression locally with or without intracranial metastases. All patients with tumor progression died. Eight patients survive with a mean cumulative follow-up of 72.4 months (range 21-152 months). No acute radiation toxicity or delayed radiation necrosis was observed among any of the 12 patients. The majority of patients who achieved tumor eradication (80%) and tumor stabilization (67%) after GKS had residual tumor as the reason for their referral for GKS. The best outcomes were attained in patients with residual disease who were younger, had smaller tumor volumes, had no evidence of metastatic disease, and had received higher cumulative GKS doses. CONCLUSIONS: Single or multiple GKS sessions were a well-tolerated, feasible, and effective adjunctive treatment for posterior fossa residual or recurrent medulloblastoma as well as intracranial metastatic medulloblastoma in adult patients.

OBJECTIVE: Stereotactic radiosurgery has become an important primary or adjuvant minimally invasive management strategy for patients with intracranial meningiomas with the goals of long-term tumor growth prevention and maintenance of patient neurological function. We evaluated clinical and imaging outcomes of meningiomas stratified by histological tumor grade. METHODS: The patient cohort consisted of 972 patients with 1045 intracranial meningiomas managed during an 18-year period. The series included 70% women, 49% of whom had undergone a previous resection and 5% of whom had received previous fractionated radiation therapy. Tumor locations included middle fossa (n = 351), posterior fossa (n = 307), convexity (n = 126), anterior fossa (n = 88), parasagittal region (n = 113), or other (n = 115). RESULTS: The overall control rate for patients with benign meningiomas (World Health Organization Grade I) was 93%. In those without previous histological confirmation (n = 482), tumor control was 97%. However, for patients with World Health Organization Grade II and III tumors, tumor control was 50 and 17%, respectively. Delayed resection after radiosurgery was necessary in 51 patients (5%) at a mean of 35 months. After 10 years, Grade 1 tumors were controlled in 91% (n = 53); in those without histology, 95% (n = 22) were controlled. None of the patients developed a radiation-induced tumor. The overall morbidity rate was 7.7%. Symptomatic peritumoral imaging changes developed in 4% of the patients at a mean of 8 months. CONCLUSION: Stereotactic radiosurgery provided high rates of tumor growth control or regression in patients with benign meningiomas with low risk. This study confirms the role of radiosurgery as an effective management choice for patients with small to medium-sized symptomatic, newly diagnosed or recurrent meningiomas of the brain.

OBJECTIVES: The purpose of this study was to evaluate the results following Gamma Knife thalamotomy (GKT) for medically refractory essential tremor in a series of patients in whom open surgical techniques were not desirable. METHODS: Thirty-one patients underwent GKT for disabling essential tremor after medical therapy had failed. Their mean age was 77 years. Most patients were elderly or had concomitant medical illnesses. A single 4-mm isocenter was used to target a maximum dose of 130 or 140 Gy to the nucleus ventralis intermedius. Items from the Fahn-Tolosa-Marin clinical tremor rating scale were used to grade tremor and handwriting before and after radiosurgery. RESULTS: The median follow-up was 36 months. In the group of 26 evaluable patients, the mean tremor score (+/- standard deviation) was 3.7 +/- 0.1 preoperatively and 1.7 +/- 0.3 after radiosurgery (p < 0.000015). The mean handwriting score was 2.8 +/- 0.2 before GKT and 1.7 +/- 0.2 afterward (p < 0.0002). After radiosurgery, 18 patients (69%) showed improvement in both action tremor and writing scores, 6 (23%) only in action tremor scores, and 3 (12%) in neither tremor nor writing. Permanent mild right hemiparesis and speech impairment developed in 1 patient 6 months after radiosurgery. Another patient had transient mild right hemiparesis and dysphagia. CONCLUSIONS: Gamma Knife thalamotomy is a safe and effective therapy for medically refractory essential tremor. Its use is especially valuable for patients ineligible for radiofrequency thalamotomy or deep brain stimulation. Patients must be counseled on potential complications, including the low probability of a delayed neurological deficit.

Advances in central nervous system imaging have resulted in early detection of a greater number of intracanalicular vestibular schwannomas. Early detection of intracanalicular vestibular schwannomas raises the issue of whether or not treatment is required and, if so, whether radiosurgery is the most appropriate option. Available evidence indicates that a majority of intracanalicular lesions are observed to grow and most will be associated with progressive hearing loss or, less frequently, sudden persistent hearing loss. If the objective of treatment is to preserve serviceable binaural hearing, early intervention is advisable. Early intervention is advantageous only if serviceable hearing can be maintained in the majority of patients along with low perioperative morbidity. Radiosurgery seems to achieve these goals ideally. Radiosurgery is a minimally invasive management option for patients with intracanalicular tumors. Radiosurgery provides high rate of long-term hearing preservation with minimal morbidity.