Faculty Bibliography

Because pentobarbital has been shown to reduce cerebral toxicity to single-fraction whole brain irradiation in a rat model, we sought to evaluate its cerebral radioprotective effects for stereotactic radiosurgery. We hypothesized that concurrent high-dose pentobarbital anaesthesia (50 mg kg-1) during irradiation could delay or prevent the onset of radiation necrosis within the radiosurgical volume. Six rats were placed in pentobarbital or control groups, irradiated, and then evaluated at different intervals (60, 100, 150, 365 days; total = 48 animals studied). All rats had 100 Gy radiosurgery to the right frontal brain region (a threshold dose for focal necrosis at 90 days). The radioprotective effects of pentobarbital were compared to ketamine anaesthesia (control) and evaluated for observed focal necrosis, size of necrotic lesion, blood vessel alterations, and to changes in cell nuclei. There was no difference between groups in the numbers of rats with necrosis at 100 days (p = 0.72), at 150 days (p = 0.77), or at 365 days (p = 0.77); no necrosis was observed in either group at 60 days. There was no difference in the size of the necrotic lesion at 100 days (p = 1.0), at 150 days (p = 0.39), or at 365 days (p = 0.07). There was no difference between groups in observed blood vessel changes or nuclear changes at any time interval (p > 0.6). There was no animal morbidity related to radiosurgery.(ABSTRACT TRUNCATED AT 250 WORDS)

Because conventional stereotactic angiography provides only two-dimensional information for dose planning, we studied the accuracy and usefulness of stereotactic magnetic resonance angiography (sMRA) for arteriovenous malformation (AVM) radiosurgery in 28 consecutive patients. We hypothesized that the multidimensional data set provided by sMRA and the opportunity to image both blood vessels and brain parenchyma would improve the accuracy of AVM irradiation and improve the safety of radiosurgery. Twenty-eight patients with AVMs in different brain locations and with a variety of AVM sizes (range, 15-31 mm mean diameter) had sMRA followed by stereotactic angiography. The sMRA images only were used to construct an initial radiosurgical plan. This plan was then used to outline the AVM volume defined by conventional angiography. In 24 patients, sMRA information equaled that of conventional angiography. In 3 patients, sMRA was better, because conventional angiography overestimated the size of the AVM nidus. In one patient, the conventional angiogram showed a second separate nidus (10-mm diameter) that was not as well defined on MRA. There were no complications with any procedure. In 16 patients (57%), sMRA provided critical information on AVM shape that was not provided by conventional angiography alone. Stereotactic MRA is a fast, noninvasive, inexpensive, multidimensional imaging method for AVM radiosurgery that provides information on vascular and parenchymal brain anatomy important for optimal dose planning. We believe that it can be used with confidence as the sole imaging method for medium-size, compact-nidus AVMs.

To define the outcomes after stereotactic radiosurgery performed for smaller volume arteriovenous malformations (AVMs) that are potentially suitable for surgical removal, we retrospectively reviewed our 4-year experience in 65 patients who declined microsurgery. All 65 patients had Spetzler-Martin Grade I or II AVMs and a minimum follow-up of 24 months (median, 29 mo). Symptomatic improvement after radiosurgery occurred in 52% of patients with seizures and in 63% of patients with headaches. The annual risk of AVM hemorrhage during the latency interval after radiosurgery was 3.7%. Five patients (7.7%) had a subsequent hemorrhage (all within 8 mo of radiosurgery); two died, and three recovered (one after hematoma evacuation and two with conservative management). Forty-seven patients (72%) returned to their previous employment status or activity level within 1 week of radiosurgery (92% within 1 yr). No patient suffered radiation-related complications. Twenty-seven (84%) of 32 patients evaluated by postradiosurgical angiography had complete AVM obliteration. Radiosurgery is an effective and less invasive management strategy for Grade I or II AVM patients who are either medically unsuitable for or unwilling to undergo surgical removal. The risk of AVM hemorrhage during the latency interval until obliteration occurs appears to be no different than the natural history of untreated AVMs. These results (including hemorrhage prevention and symptom amelioration) indicate that the conservative management of small AVMs can rarely be justified.

To evaluate the reported benefit of ipsilateral single-application ophthalmic anesthetic eyedrops in patients with typical trigeminal neuralgia, a randomized double-blind placebo-controlled trial was performed. Forty-seven patients were randomly assigned to receive two drops of either proparacaine (25 cases) or saline placebo (22 cases). The experimental and placebo groups were equivalent in regard to patient age, distribution of trigeminal neuralgia pain, duration of pain, current medication regimens, and number of prior procedures performed. Pain response was assessed at 3, 10, and 30 days after instillation using two pain rating scales and a measure of pain frequency. Treatment failure was defined in advance as any of the following: a lack of clinical response, the need for an increase in medication, or the need for surgery. No significant difference in outcomes was found between the two groups either when using a verbal pain rating scale (p = 0.24) or when comparing overall pain status (unchanged, improved throughout the study period, or temporarily improved) (p = 0.98). No difference in the frequency of trigeminal neuralgia attacks between the two treatment groups (scaled within five levels of pain frequency) was detected (p = 0.09). During follow-up monitoring, 11 patients in the test drug group and 14 in the placebo group required surgery because of persistent pain (p = 0.24). The results of this study indicate that single-application topical ophthalmic anesthesia reduces neither the severity nor the frequency of pain in comparison to placebo administration. Although a simple and safe treatment, the single application of topical ophthalmic eyedrops provides no short- or long-term benefit to patients with trigeminal neuralgia.

Twenty patients with acoustic nerve tumors (mean diameter < or = 30 mm) and useful preoperative hearing were examined 2 years after stereotactic radiosurgery to determine the effectiveness of the surgery in the control of tumor growth and the preservation of cranial nerve function. Results showed tumor volume stabilization (12 cases) or reduction (seven cases) was achieved in a total of 19 patients (95%). Useful hearing (defined as Gardner and Robertson Class I or II) preservation was obtained in 100% of cases immediately postoperatively, 50% at 6 months, and 45% at both 1 and 2 years. Two years after stereotactic radiosurgery, facial nerve function was preserved in 90% of patients and 75% continued to have normal trigeminal nerve function. All patients returned to and maintained their preoperative functional status within 3 to 5 days after radiosurgery. These findings indicate that stereotactic radiosurgery with multiple isocenters and narrow radiation beams is a safe and effective management strategy for progressive acoustic nerve tumors. Auditory, facial, and trigeminal nerve function can be preserved in most patients. Prevention of further growth and preservation of cranial nerve function appear to be satisfactory goals in the current management of patients with acoustic neuromas.

A bullet, lodged in the pineal-posterior region of the third ventricle and causing obstructive hydrocephalus, was removed without damage to critical adjacent vascular structures using stereotactic localization followed by laser-guided stereotactic craniotomy. Stereotactic techniques provided precise target localization and allowed dissection to be restricted to the previously injured missile track, thus avoiding any additional morbidity from the surgical procedure.