Intraoperative ultrasonography of extramedullary spinal tumours.

Intraoperative spinal sonography (IOSS) was performed in 28 patients with extramedullary spinal tumours. Images were obtained of 31 tumours, because 2 patients had multiple tumours. There were 17 neurilemmomas, 9 meningiomas and 2 dermoid cysts. All tumours appeared well-defined and highly echogenic. There was no difficulty differentiating extramedullary spinal tumours from intramedullary masses excepting case, a big neurilemmoma at the conus medullaris. All images were assessed with reference to the surface of the lesions, the existence of cysts, and movement. Neurilemmomas had smooth surfaces, some cysts, and exhibited a "floating" movement. Meningiomas had irregular surfaces, were more highly echogenic than neurilemmomas, and adhered tightly to the dura mater. However, some neurilemmomas and meningiomas did not have these, and it was not always possible to differentiate them. Although IOSS has limitations of resolution, it gave useful information about the size of the tumours, the degree of displacement of the spinal cord, and even about the type of tumour in some cases. It was extremely helpful to the surgeon.