Ultrasound-guided Microwave Ablation for the Management of Inguinal Neuralgia: A Preliminary Study with 1-Year Follow Up

Clinical question 
Is MWA effective in treating post-surgical inguinal neuralgia.

Take away point
MWA was able to treat chronic inguinal neuralgia in short and medium term without adverse outcomes.

Study design 
Retrospective review of 12 procedures (10 patients)

Funding Source 
No reported funding.

Setting
Academic hospital, University of Wisconsin School of Medicine and Public health.

Click here for abstract

Summary
Inguinal neuralgia affects 12% of inguinal herniorrhaphy patients. Patients present with burning or throbbing pain in the groin and proximal and medial thigh. Chronic inguinal neuralgia (> 6 weeks) has limited improvement with oral medication, surgery, nerve blocks etc. This study evaluated the safety and efficacy of microwave ablation (MWA) in the treatment of chronic inguinal neuralgia.

Ten patients (12 procedures) were evaluated retrospectively. Patients included in this study had a positive response to an ultrasound-guided nerve block (steroid and anesthetic) of the ilioinguinal, iliohypogastric or genitofemoral nerve. Patients were considered to have had a positive response if they had a pain reduction score of more than 2 points on the VAS scale for at least 2 hours, and were treated when their pain returned to baseline.

Successful placement of the MW antenna next to the culprit nerve was confirmed by using a short MW pulse that reproduced the patient’s pain. MWA was performed under sedation using 3 cycles of 30 watts for 30 seconds. Phone call follow up was performed at 1, 6 and 12 months using the VAS scores. Clinical success was considered as 2-point decrease in VAS score.

Mean baseline VAS score was 6.1 (SD 2.5), immediately post procedure 2.2 (SD 2.4), at 1, 6 and 12 months, 0.8 (SD 1.5), 1.5 (SD 2.0), and 2.0 (SD 2.7) respectively. Significant pain improvement was seen at all time points, and at 12 month follow up there was significant pain relief in 10/12 procedures, with an average pain relief reduction of 10.5 months. Mean procedure time was 43.3 minutes (range, 20-60 minutes), and no adverse events were observed.

The authors highlight the advantages of MWA over RF, which include faster tissue heating, reproducible treatment zones, less susceptibility to heat-sink, etc. The authors also mention that cryoablation has also been used in the treatment of inguinal neuralgia with 78% clinical success in 10 patients, which make it similar to the results presented in this study. Ultrasound targeting of the nerves allows direct visualization of the nerve when compared to CT that uses landmarks for nerve targeting. Reasons for clinical failure in 2 patients, the authors hypothesize, included the initial targeting of the ilioinguinal nerve, as well as normal anatomical variants that can cause overlap in symptoms between the 3 main nerves involved in inguinal neuralgia.

The main limitations of the study include, retrospective design of the study, lack of control group, and lack of standardized follow up. Regardless of the limitations, this study provides encouraging data that supports the use of MWA for the treatment of inguinal neuralgia. Larger studies, with a control group and longer follow up are needed to validate these findings.

Figure 1- Intra-procedural MWA showing the inferior epigastric artery (red arrow), genitofemoral nerve (arrow head), MWA antenna (arrows), and hernia mesh (curved arrows). 

Commentary 

Currently, patients with post-surgical chronic inguinal neuralgia have limited options with the authors providing data supporting the use of MWA for pain control. Patients included in this study had successful nerve block, which confirmed the culprit nerve. It remains unclear why 1 patient had a positive response to the nerve block and no response to MWA. Ultrasound targeting of the nerve provides a more accurate modality to ensure successful needle placement adjacent to the nerve. Overall, 10/12 procedures showed clinical improvement at 12 months, which is very promising. As the authors mentioned a larger study (with longer follow up) including a control group, and possibly comparison to cryoablation, is necessary to validate MWA as the modality of choice in the treatment of inguinal neuralgia.

Post Author
Carlos J. Guevara, MD, FSIR
Assistant Professor
Department of Radiology, Interventional Radiology Division
University of Texas Health Sciences, Houston
@CarlosGuevaraIR