Endoneurosonography: technique and equipment, anatomy and imaging, and clinical application

To evaluate the usefulness of transendoscopic ultrasound in neurosurgery, we studied two new sonoprobes measuring 6 and 8 French in diameter in 20 fresh specimens. The application and indication are discussed in the first clinical series of 75 patients.

Sonocatheters (ALOKA, Meerbusch, Germany) 1.9 mm (6 French) and 2.4 mm (8 French) in diameter were introduced into the working channel of an endoscope. The preparations were done in nonfixed skulls in a surgical simulation-setting laboratory. Based on these experiences with imaging possibilities, intraoperative transendoscopic ultrasound was applied in 75 patients and a variety of lesions. It was used for imaging (41 patients), targeting (18 patients), and neuronavigation (16 patients) in neuroendoscopy.

The sonoprobe adds a transverse scan at the tip of the probe to the anterior endoscopic view. This axial scan to the longitudinal axis of the endoscope is geometrically comparable with radar scanning. Three probes working with 10, 15, and 20 MHz were used, resulting in a short penetration with a radius of 3 cm. The orthogonal scanning plane had limitations, which were documented. We observed precise imaging of well known anatomic structures and, moreover, achieved an additional dimension in endoscopy. The axial scan presents the anatomic landmarks like a map at the tip of the endoscope where the endoscope is represented as a spot. The real-time imaging and representation of the tip of the endoscope showed a capacity for navigation. This preclinical study rectified clinical application. The real-time imaging of this technique showed the ability of the navigation of endoscopes to detect more overall movements, such as blood flow or change of ventricle size during endoscopy. The primary benefit in this first clinical series was witnessed in difficult endoscopy cases and complex lesions, but benefit was also observed in cases in which vision through the endoscope alone was obscured. The main limitation was the result of little penetration depth and lack of anterior scanning.

Application of transendoscopic ultrasound is appropriate in neurosurgery. Training is necessary to understand the imaging and the geometry of scans because this technique does not scan along the axis of the endoscope. Further development to overcome the current limits of this technique and more clinical experience are needed.