Optimal outcomes for hearing preservation in the management of small vestibular schwannomas.

OBJECTIVE: To undertake a systematic review of the role of microsurgery, in relation to observation and stereotactic radiation, in the management of small vestibular schwannomas with serviceable hearing. METHODS: The Medline database was searched for publications that included the terms 'vestibular schwannoma' and/or 'acoustic neuroma', occurring in conjunction with 'hearing'. Articles were manually screened to identify those concerning vestibular schwannomas under 1.5 cm in greatest dimension. Thereafter, only publications discussing both pre-operative and post-operative hearing were considered. RESULTS: Twenty-six papers were identified. Observation is an acceptable strategy for small tumours with slow growth where hearing preservation is not a consideration. In contrast, microsurgery, including the middle fossa approach, may provide excellent hearing outcomes, particularly when a small tumour has begun to cause hearing loss. Immediate post-operative hearing usually predicts long-term hearing. Recent data on stereotactic radiation suggest long-term deterioration of hearing following definitive therapy. CONCLUSION: In patients under the age of 65 years with small vestibular schwannomas, microsurgery via the middle fossa approach offers durable preservation of hearing.

Comparative tracking error analysis of five different optical tracking systems.

OBJECTIVE: Effective utilization of an optical tracking system for image-based surgical guidance requires optimal placement of the dynamic reference frame (DRF) with respect to the tracking camera. Unlike other studies that measure the overall accuracy of a particular navigation system, this study investigates the precision of one component of the navigation system: the optical tracking system (OTS). The precision of OTS measurements is quantified as jitter. By measuring jitter, one can better understand how system inaccuracies depend on the position of the DRF with respect to the camera. MATERIALS AND METHODS: Both FlashPointtrade mark (Image Guided Technologies, Inc., Boulder, Colorado) and Polaristrade mark (Northern Digital Inc., Ontario, Canada) optical tracking systems were tested in five different camera and DRF configurations. A linear testing apparatus with a software interface was designed to facilitate data collection. Jitter measurements were collected over a single quadrant within the camera viewing volume, as symmetry was assumed about the horizontal and vertical axes. RESULTS: Excluding the highest 5% of jitter, the FlashPoint cameras had an RMS jitter range of 0.028 +/- 0.012 mm for the 300 mm model, 0.051 +/- 0.038 mm for the 580 mm model, and 0.059 +/- 0.047 mm for the 1 m model. The Polaris camera had an RMS jitter range of 0.058 +/- 0.037 mm with an active DRF and 0.115 +/- 0.075 mm with a passive DRF. CONCLUSION: Both FlashPoint and Polaris have jitter less than 0.11 mm, although the error distributions differ significantly. Total jitter for all systems is dominated by the component measured in the axis directed away from the camera.

Remote-rendered 3D CT angiography (3DCTA) as an intraoperative aid in cerebrovascular neurosurgery.

OBJECTIVE: To assess the viability and utility of network-based rendering in the treatment of patients with cerebral aneurysms, we implemented an intraoperative rendering system and protocol using both three-dimensional CT angiography (3DCTA) and perspective volume rendering (PVR). MATERIALS AND METHODS: A Silicon Graphics InfiniteReality engine was connected via a Fast Ethernet network to a workstation in the neurosurgical operating room. A protocol was developed to isolate bone and vessels using an appropriate transfer function. Three-dimensional CT angiogram images were volume rendered and transmitted to the workstation using a bandwidth-conserving remote rendering system, and were rotated, cut using clipping planes, and viewed using normal and perspective views. Twelve patients with intracranial aneurysms were examined at surgery using this system. RESULTS: Rendering performance at optimal operating bandwidths (50-60 Mb/s) was excellent, with regeneration of a high-resolution image in less than 1 s. Network performance varied in two cases, slowing image regeneration. Surgeons found the images to be useful as an adjunct to conventional imaging in understanding the morphology of complex aneurysms and their relationship to the skull base. CONCLUSIONS: Intraoperative volume rendering using 3DCTA is achievable over a network, can reduce hardware costs by amortizing hardware among multiple users, and provides useful imaging information during the surgical treatment of cerebral aneurysms. Future operating suites may incorporate network-transmitted three-dimensional images as additional sources of imaging information.