Innovative Use of the O-Arm for Skull Base Resection in a Sphenoorbital Meningioma

Introduction: Bone-invasive sphenoid wing meningiomas are typically associated with hyperostosis of adjacent bone. Gross total resection is the standard operative goal, and reoperation is often considered if postoperative imaging demonstrates incomplete resection or persistent neural compression. We report our experience with intraoperative computed tomography (iCT) using the Medtronic O-arm to evaluate the extent of resection of hyperostotic bone secondary to an en plaque sphenoorbital meningioma.

Case Report: A 43-year-old woman presented with a right-sided sphenoid wing meningioma causing proptosis secondary to hyperostosis of the sphenoid bone. We performed an orbitozygomatic craniotomy for resection of the hyperostotic bone at the skull base with the patient placed in standard metallic head holder and cranial fixation pins. The superior orbital fissure, foramen rotundum, and foramen ovale were decompressed. An iCT of the skull base was then obtained after initial decompression using the O-arm, and the images were used to guide further decompression of the lateral orbital wall prior to closure.

Discussion: Using iCT for intracranial pathology has been reported since 1987. However, its availability has grown substantially since then with the widespread implementation of portable, much more practical iCT devices. Portable iCT use has mostly been reported in spine surgery, although more recently it has been reported in use for functional neurosurgery. The majority of reported intracranial applications have involved electrode placement verification for deep brain stimulation. Various iCT devices have been developed; however, limitations in the gantry size necessitate specialized radiolucent head holders. The larger open-ring gantry configuration of the widely available O-arm allows more flexibility in obtaining the scan intraoperatively.

Conclusion: We used iCT to intraoperatively evaluate the adequacy of bony decompression of hyperostosis secondary to an en plaque sphenoorbital meningioma. This case illustrates an innovative intracranial application of a device most frequently used in spine surgery. The O-arm is ideal for tailoring skull base resections intraoperatively, and a standard metallic head holder can be used. Furthermore, this device may be more widely available in hospitals than other devices capable of three-dimensional intraoperative imaging. In the future, soft tissue optimization for the O-arm may expand its intracranial imaging applications.