Use of a Simple Internal Fiducial as an Adjunct to Enhance Intraoperative Ultrasound-Assisted Guidance: Technical Note

Abstract

Image-based navigational techniques have been used increasingly in neurosurgery to improve intraoperative precision. These techniques, however, have the disadvantage of inherent inaccuracies, which are significant especially when targeting small, subcortical lesions in eloquent areas. Intraoperative ultrasound serves as a useful, real-time adjunct to these techniques, but at times, precise correlation of the true anatomical location to the ultrasound image can be challenging. : To improve the accuracy and precision of intraoperative ultrasound by using a simple internal fiducial marker made from materials already present on the sterile field. We present 3 cases (2 cranial, 1 spinal) of small lesions with deep and eloquent locations. Magnetic resonance imaging (MRI)-based frameless stereotaxy or spinal fluoroscopy was used to modify the incision and to approximate the surgical trajectory, which was marked intradurally with a small piece of Gelfoam soaked in autologous blood. Ultrasound was used to visualize the echogenic lesion, and the precise trajectory was then refined using the echogenic blood-soaked Gelfoam on the cortical or spinal cord surface. In all 2 patients, the combined use of MRI-based frameless stereotaxy (cranial cases only) and ultrasound guidance minimized dissection through normal tissue. All cases resulted in a gross total resection and no added long-term surgical morbidity. We describe a neuronavigational tool to aid in the precise localization of a subcortical or spinal lesion, particularly one that is small and in close proximity to eloquent areas.