Utility of intraoperative ultrasound for tumors of the cauda equina

Study Design. A retrospective chart review of patients with tumors of the cauda equina was performed. Objectives. To assess the role of intraoperative ultrasound for detecting tumor migration and modifying the approach to cauda equina tumors. Summary of Background Data. Rostral migration of cauda equina tumors relative to preoperative imaging is well described. The utility of intraoperative ultrasound to identify tumor migration and to modify the surgical approach was analyzed. Methods. The medical records of nine consecutive patients undergoing biopsy or resection of a cauda equina tumor diagnosed by magnetic resonance imaging at the authors' institution from January 1994 through December 2000 were reviewed. Four patients with tumors of the cauda equina underwent transdural sonography of the intraspinal compartment after initial laminectomy and before durotomy. Results. In three patients, the findings on intraoperative ultrasound showed rostral migration of the lesion with respect to the preoperative magnetic resonance imaging, necessitating additional laminectomy and modifying the site of durotomy. One tumor had migrated rostrally one full bony vertebral segment, whereas two tumors each had migrated one half of a bony vertebral segment. Pathology examination in the three patients whose lesions had migrated rostrally demonstrated a schwannoma in every case. In one patient, intraoperative ultrasound showed no lesion migration with respect to the preoperative magnetic resonance imaging, and no modifications to the surgical approach were needed. Pathology examination of this patient demonstrated an ependymoma. Conclusions. Intraoperative ultrasound was useful in documenting rostral migration of cauda equina tumors, and facilitated appropriate laminectomy and durotomy. The technique may be particularly valuable for schwannomas of the cauda equina, which seem to have a greater potential for rostral migration.