Intraoperative Spinal Sonography

B-mode real-time ultrasonography using linear and sector scanning probes of 5 or 7.5 MHz was applied during 17 operations for the following spinal cord lesions: five syringomyelias, one arachnoid cyst, eight intramedullary tumors (three benign astrocytomas, three hemangioblastomas, one ependymoma, and one subependymoma), one intradural extramedullary tumor (neurinoma), and two lipomas with spina bifida. Preoperative computed tomography (CT) scan was performed with a Somatom II scanner. Following laminectomy the wound was filled with a sterile solution and scanning was performed through this “water path” before the dura was opened. Five of eight intramedullary tumors (one benign astrocytoma, one subependymoma, two hemangioblastomas, and one ependymoma) were enhanced on CT, whereas three (two benign astrocytomas and one hemangioblastoma) were not enhanced. Three lesions (two hemangioblastomas and one ependymoma) were hyperechoic on intraoperative spinal sonography (IOSS), while five (three benign astrocytomas, one subependymoma, and one hemangioblastoma) were isoechoic. One intradural extramedullary tumor (neurinoma) was enhanced on CT and hyperechoic on IOSS. Two lipomas showed low density on CT but were hyperechoic on IOSS. Ten of 13 syrinxes or cysts (five syringomyelias, one arachnoid cyst, one benign astrocytoma, one subependymoma, one hemangioblastoma, and one ependymoma) were identified with CT, but three (one benign astrocytoma and two hemangioblastomas) were not defined. Twelve of these 13 lesions were anechoic on IOSS, and multiple cysts were detected. One cyst that was identified with IOSS had not been identified preoperatively. Masses and cysts were visualized more clearly with the 7.5 MHz transducer than with the 5 MHz transducer. However, one very small lesion was not detected, and the probe is large. Therefore, a transducer of higher frequency should be developed for the spinal cord. IOSS is noninvasive and demonstrates the precise size and location of the lesion in real time, so the lesion can be approached with minimum damage to the spinal cord. This technique is extremely useful and should be applied in all surgery for spinal cord lesions.