Intraoperative Ultrasound Imaging Features Guiding Surgical Strategy in Spinal Cord Ependymoma Resection

Preoperative imaging provides surgeons with an initial estimate of tumor infiltration and the likelihood of achieving an en-bloc resection in spinal cord ependymomas, yet the definitive decision is made intraoperatively. This study characterizes the intraoperative ultrasound (iUS) features that guide real-time surgical strategy and are associated with successful en-bloc removal.

A retrospective review of iUS images obtained during resection of spinal cord ependymomas was performed. The presence of a peritumoral halo representing the transition zone between the tumor and the spinal cord, the dorsal sagittal area of the spinal cord overlying the tumoral poles, the presence and location of tumor cysts, and the diameter of the compressed spinal cord located ventral and dorsal to the tumor were assessed. Demographic and surgical data including extent and technique of resection, occurrence of intraoperative neurophysiological changes, and preoperative and postoperative neurological status were collected.

The mean dorsal sagittal area of the spinal cord overlying the cranial pole was 0.1 cm² (range 0-0.23 cm²), whereas the area overlying the caudal pole was 0.05 cm² (range 0-0.16 cm²). All tumors exhibited a peritumoral halo, ranging from 0° to 360° in the axial view. The echogenicity of the halo was predominantly hypoechoic. Gross total resection was achieved in all cases, with en-bloc technique performed in 57% of patients. Intraoperative changes in somatosensory and motor evoked potentials were observed in all cases. Nevertheless, clinically, all patients remained neurologically stable in the postoperative period compared with preoperative.

iUS identifies useful imaging features that allow surgeons to develop a structured resection plan before spinal cord manipulation. Future longitudinal studies are needed to validate whether the presence of a peritumoral halo or the extent of sagittal spinal cord area overlying the tumor poles are predictors of neurological and oncological outcomes.