Faculty Bibliography

The authors made a review of a series of patients with hemangioblastomas of the posterior fossa treated between 1973 and 1993. A total of 32 patients were analyzed with 24 patients receiving resection, 8 patients receiving radiosurgery and 2 patients receiving conventional radiotherapy. The mortality in the patients with a resection was considered acceptable with 2 deaths (8%) and with a morbidity of 3 patients (12.5%). A review of the literature suggests that conventional radiotherapy with high doses (45-60 Gy) may have a role in the post-operative control of hemangioblastomas and in some cases could be employed even before the resection in order to facilitate the surgery. The radiosurgical treatment is regarded like adjuvant. Poor results were obtained with radiosurgery in large tumors where low doses (less than 20 Gy) were used. Because of the rarity and complexity of these tumors, mainly when associated with von Hippel-Lindau disease, a multicenter study could be useful with the assessment of the optimal utilization and combination of these treatment modalities.

PURPOSE/OBJECTIVE: To assess the relationships of radiosurgery treatment parameters to the development of complications from radiosurgery for arteriovenous malformations (AVM). METHODS AND MATERIALS: We evaluated follow-up imaging and clinical data in 307 AVM patients who received gamma knife radiosurgery at the University of Pittsburgh between 1987 and 1993. All patients had regular clinical or imaging follow up for a minimum of 2 years (range: 24-96 months, median = 44 months). RESULTS: Post-radiosurgical imaging (PRI) changes developed in 30.5% of patients with regular follow-up magnetic resonance imaging, and were symptomatic in 10.7% of all patients at 7 years. PRI changes resolved within 3 years developed significantly less often (p = 0.0274) in patients with symptoms (52.8%) compared to asymptomatic patients (94.8%). The 7-year actuarial rate for developing persistent symptomatic PRI changes was 5.05%. Multivariate logistic regression modeling found that the 12 Gy volume was the only independent variable that correlated significantly with PRI changes (p < 0.0001) while symptomatic PRI changes were correlated with both 12 Gy volume (p = 0.0013) and AVM location (p = 0.0066). CONCLUSION: Complications from AVM radiosurgery can be predicted with a statistical model relating the risks of developing symptomatic post-radiosurgical imaging changes to 12 Gy treatment volume and location.

Intracavitary irradiation is reported as an additional treatment for intracranial arachnoid cysts that do not communicate with the subarachnoid space. A 46-year-old woman with a large suprasellar arachnoid cyst that had enlarged over a 4-year interval presented with new onset headaches. Stereotactic intracavitary irradiation was performed using colloidal phosphorus-32 as an alternative to craniotomy or insertion of a shunt. Total regression of the cyst occurred within one month with resolution of her headaches. After three years of follow-up, imaging studies showed only an empty sella appearance, and no cyst recurrence. No early or delayed morbidity occurred. Intracavitary irradiation may be a useful therapy for arachnoid cysts, in an attempt to alter the biology of the cyst lining.

Posteroventral pallidotomy (PVP) has received renewed interest as an ablative procedure for the symptomatic treatment of Parkinson's disease. In previous reports, the proximity of the optic tract to the lesion target in the globus pallidus internus has resulted in the occurrence of visual field deficits in as much as 14% of patients. The authors have used intraoperative visual evoked potentials (VEPs) during PVP to reduce this risk. All procedures were performed in awake patients. Flash stimuli were delivered to each eye via fiberoptic sources. Baseline flash VEPs were recorded at O1/Cz (left visual cortex to vertex), Oz/Cz (midline visual cortex to vertex), and O2/Cz (right visual cortex to vertex) for OS, OU, and OD stimulation. Epochs were acquired before and after localization, after macroelectrode stimulation, after temporary thermal lesioning, and after permanent thermal lesioning. Forty-seven patients underwent a total of 59 procedures. Visual evoked potentials were recorded reproducibly in all patients. In 11 procedures, VEP changes were reported, including six amplitude changes (10-80%), six latency shifts (3-10 msec), and one report of "variability." In four procedures, VEP changes prompted a change in target coordinates. One false-positive and one false-negative VEP change were encountered. The only confirmed visual deficit was a superior quadrantanopsia, present on formal fields, but clinically asymptomatic. The authors conclude that VEPs may be useful for procedures performed in the awake patient because of the lack of anesthetic-induced variability. The 1.7% visual morbidity reported here (one in 59 patients) compares favorably with other series using microelectrodes. Visual evoked potentials may be a useful monitoring technique to reduce the incidence of clinically significant visual morbidity during pallidotomy, especially during formal lesioning of the ventral pallidum adjacent to the optic tract.

Radiosurgery is one of the surgical treatments of trigeminal neuralgia. Through precise irradiation of the proximal trigeminal nerve identified on high-resolution imaging, pain relief can be achieved after a short latency interval. This image-guided approach has been useful for both patients with persistent pain after other surgeries, and as a primary surgical option. A minimum dose of 70 Gy delivered with the gamma knife has been associated with low risk for facial numbness, and no other morbidity. Management of trigeminal neuralgia without an incision, transfacial needle placement or nerve section may prove useful to increasing numbers of patients.

With improvements in imaging technology, the detection of both cavernous malformations and venous malformations has increased markedly in recent years. Although much has been learned about the association of cavernous and venous malformations, important questions regarding the true nature of such a relationship remain unanswered. It has been proposed that certain venous malformations produce local venous hypertension with resultant microhemorrhage, growth factor release, and creation of cavernous malformations. The authors report on two patients with cerebellopontine venous malformations associated with cavernous malformations. Both patients demonstrated persistent regional parenchymal enhancement associated with the vascular malformations. In addition, both patients had significant clinical symptoms referable to the region of affected brain. This previously undescribed finding may represent an imaging correlate to the complex interaction among venous malformations, venous hypertension, and cavernous malformations.