Surgical Navigation with the OMI System (Stereotactic and Functional Neurosurgery) Part 2

Surgical Experience with the Mayfield ACCISS System

Since its introduction in late 1994, the author has used the Mayfield ACCISS in approximately 300 image-guided assisted procedures (Table 1). A wide variety of applications has shown its versatility and dependability for the full gamut of image-guided neurosurgery with little if any time added to the procedure.

Table 1 Image-Guided Experience with the Mayfield ACCISS System

Resection of metastatic lesions can be accomplished efficiently and safely with image-guided surgery. A report of the first 41 patients operated on using the Mayfield ACCISS system showed an average time for the procedure of under 2 hours with minimal morbidity [10].

The Mayfield ACCISS for transphenoidal surgery eliminates the need for fluoroscopy. One can track the probe in the axial and coronal views as well as the sagittal view (Fig. 4). Even with the traditional use of fluoros-copy, one often struggles tracking the surgical instrument in a large tumor where the margins of the sella are poorly visualized. Both the CT (with its superb bone windows) and MRI can be simultaneously tracked in all three view planes. Removal of the fluoroscopy unit from the field is a welcome relief.

Stereotactic applications can be performed with accuracy and confidence. The rigidity of the AccuPoint sphere and the robust mechanical arm approximate the rigidity of stereotactic frames. More than 100 stereotactic procedures have been successfully performed with the Mayfield ACCISS and the AccuPoint sphere [11,12]. This includes stereotactic biopsy in 67 cases, aspiration of hematomas in 16 cases, and aspiration of intracerebral abscesses in eight cases. The diagnostic rates and complications for stereo-tactic biopsy with the Mayfield ACCISS are equivalent to the best results in the literature for stereotactic frames [11,13-16]. Coregistration of post-biopsy images confirms the efficacy of this methodology and provides documentation of stereotactic targeting in a way never demonstrated with ste-reotactic frame technology (Fig. 5).

The use of image-guided surgery in spinal applications has been more limited than cranial applications in the author’s experience of 31 cases. To use the system for placement of pedicle screws, especially when a decompression has been performed and the pedicle can be palpated, is probably not helpful but may be a good place for the beginner to gain experience. It is certainly more beneficial in cases where pedicle screws are placed and no laminectomy is performed. Patients with degenerative scoliosis, and those who require pedicle screws in the thoracic and cervical region, present a more compelling need for image-guided surgery.

The Mayfield ACCISS image-guided system has been integrated into the Mayfield® Mobile SCAN™ portable CT, which provides the surgeon the opportunity to obtain updated CT images during surgery. It also will allow the surgeon to obtain spinal images in the prone position at the time of surgery, eliminating concerns regarding spinal movement and the need for segmental registration. The mechanical arm system has also been adapted to and is compatible with intraoperative MRI systems. These adaptations provide the surgeon solutions to many concerns about the limitations of current image-guided surgery. These include the ability to obtain updated images to correct for shift and to assess the amount of residual tumor in a way that is superior to ultrasound.

CONCLUSION

Image-guided neurosurgery has many beneficial applications. The Mayfield ACCISS has many unique features that distinguish it from others in addition to its ease of use and economy for the neurosurgeon. First and foremost, it is the only system with active, wireless optical tracking and mechanical arm technology combined in one unit. This allows the surgeon to choose the digitizer most suitable to the needs of an individual case. Second, the rigidity of the AccuPoint sphere provides an unparalleled stereotactic capability for an image-guided system. Third, the coregistration capability allows one to use multimodality images during and after surgery. Fourth, the system is reliable and so simple to use that additional personnel are not required to operate the system for the surgeon. Lastly, the adaptation of the Mayfield ACCISS to intraoperative CT or MRI ensures its utility as neurosurgeons adopt these technologies.