2025 Volume 16 Issue 7 Pages 1030-1039
Introduction: Ultrasound technology allows real-time visualisation of needle placement near a nerve and the spread of a local anaesthetic solution around it. In this study, we explored the feasibility of long-axis ultrasound imaging for hydrodissection of the pudendal nerve (PDN).
Methods: This was a retrospective case series involving seven patients with a tentative diagnosis of PDN entrapment. Each patient underwent ultrasound-guided PDN hydrodissection. After obtaining transverse images of the ischial spine, a low-frequency convex probe was slightly rotated to capture the PDN in long-axis views, in which the PDN runs just infra-medial to the ischial spine, following a straight path approximately 10° ventral to the paramedian long axis of the body. On longitudinal scans, the PDN appeared as a tubular structure with hypoechoic nerve fascicles separated by hyperechoic perineurial connective tissue bands. A 22-gauge needle was carefully inserted on the caudal side, and its tip position was confirmed using small-volume local anaesthetic injections. Once correct placement was verified on the surface of the nerve, an additional dose of local anaesthetic solution (maximum 4 mL in total) was administered, and its spread was observed in real time using long-axis imaging.
Results: In patients with PDN entrapment, especially in severe cases, the boundary between the nerve and surrounding tissue appeared blurred because of the coarsely hyperechoic surrounding tissue. Despite this, PDN was successfully identified in all patients. The injected local anaesthetic solution appeared as a hypoechoic collection, highlighting the nerve surface and confirming successful hydrodissection. Based on a positive response to anaesthetic infiltration, a final diagnosis of PDN entrapment was made in four patients. In four patients, including three without PDN entrapment, the injection completely freed the PDN from the ischial spine and the sacrotuberous ligament. With a one-time injection using this technique, one patient with PDN entrapment experienced long-lasting (> 12 months) relief from perineal pain and pollakiuria (micturition > 20 per day). However, two PDN entrapment patients with a long history of symptoms required open surgical dissection, as repeated hydrodissection (3 and 10 times) failed to achieve complete nerve release from the surrounding tissue.
Conclusions: This case series suggests that long-axis ultrasound imaging can provide valuable insights into the effectiveness of PDN hydrodissection. It allows real-time assessment of the success of the procedure and helps determine whether or when surgical intervention is necessary. Early and timely hydrodissection may improve the treatment outcomes and reduce the need for open surgery.
