Feasibility of pudendal nerve anesthetic block using fusion imaging technique in chronic pelvic pain

Chronic perineal pain syndrome caused by pudendal nerve, is caused by the nerve entrapment between the sacrospinous and sacrotuberous ligaments (interligamentous plane) at the ischial spine and in the Alcock's canal. Pain therapists approach the problem with peripheral nerve blocks. Needle placement is done by a fluoroscopic, computed tomography (CT) or ultrasound (US) guide. The first is unable to visualize the interligamentous plane and it exposes the patient to potentially harmful ionizing radiations. CT scan allows the visualization of the interligamentous space and of Alcock's canal, but it is lacking real-time visual control. US alone ensures real-time needle advancement and confirmation of injective spread within the interligamentous plane but it's usually combined with intraoperative fluoroscopy because at the depth of the ischial spine (usually more than 7 cm) the resolution should be suboptimal. We tried to improve pudendal anesthetic block using fusion real time imaging between US and CT. The system combines, in real time, US imaging with previous magnetic resonance (MR) or CT data. Imaging fusion is possible through the identification of anatomical landmarks of the same patient obtained by the different imaging modalities. Fusion imaging could help to avoid multiple exposures to ionizing radiations, improving costs and quality. We decided to verify the potential of this technique, normally employed to guide interventional imaging, to peripheral anesthetic block, testing its feasibility.