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University Hospital Innsbruck Innsbruck 6020, Austria
We read the article by Hough et al. [1] with interest and found many parallels to articles by Gruber et al. [2] and Kovacs et al. [3] that were published in 2001. Hough et al. investigated topographic anatomy to confirm previous findings concerning the typical course of the pudendal nerve in the deep gluteal region and in the pelvic floor. Our articles in 2001 also gave exact information on topographic relations, landmarks, and variants. Hough et al. even used needle guidance in a cadaveric specimen to verify the region punctured, as we did. Our studies were performed using sonography as a real-time control for needle insertion in the pudendal nerve region of the cadaveric specimen and in volunteers. We used CT only when we verified needle position in the cadaver.
We also showed that the pudendal nerve could be accessed while avoiding the ionizing radiation used in CT. Also, our investigations on volunteers showed that sonography depicts nerve infiltration vessels in the superficial and deep gluteal regions by means of the duplex mode. This is not possible using CT scans, which do not present vascular structures as well.
Disagreement continues about which agents to inject in infiltration therapy of the pudendal nerve and elsewhere. The combination of anesthetics and antiinflammatory agents listed by Hough et al. [1] sounds up to date but should be verified by the long-term results, which are not yet available. The need for so much local anesthetic (3 mL) in such a small region for relief of pudendal neuralgia is not surprising.
The question remains why a procedure performed easily using real-time sonographic guidance should be performed using CT. Our department treats patients using sonographic guidance and has quite acceptable outcomes.
References
Mayo Clinic Rochester, MN 55905
We thank Drs. Gruber and Bodner for their letter and the excellent points they raise about our work [1]. Their articles on the sonographic anatomy and sonographically guided technique for injection of the pudendal nerve [2, 3] are of great interest. They discuss the potential advantages of using sonography to identify the internal pudendal artery and pudendal nerve; the main advantage of sonography is its real-time depiction of the nerve and vessels during the injection of local anesthetic.
Most published studies on imaging guidance for pudendal nerve injections have used CT guidance [4–8]. Fluoroscopy can also be used for guidance [6], but CT allows more accurate needle placement. Gruber and Bodner [3] obtained good results with sonographic guidance, but to our knowledge no published studies have compared CT and sonographic guidance techniques for pudendal nerve injections. CT has one potential advantage: a small test injection of diluted contrast agent can be given to determine whether the needle position is satisfactory [1]. We have seen cases in which the needle appeared to be correctly positioned adjacent to the neurovascular bundle, but the contrast material was not injected in the correct tissue plane (e.g., within or deep in relation to the sacrospinous ligament). Pudendal neuralgia can also be caused by entrapment or irritation of the pudendal nerve more distally at the level of the pudendal (Alcock's) canal. CT is helpful when performing injections into the pudendal canal because a test injection of contrast material is needed to confirm appropriate needle position. To our knowledge, the pudendal canal has not been successfully localized with sonographic or fluoroscopic guidance.
In our practice, patients undergo a sensory examination for determination of pudendal anesthesia after the CT-guided nerve block. This, along with a small test injection of diluted contrast material, has allowed us to improve our skill with needle placement and achieve the highest possible clinical success. A difference in needle position of as little as 1–2 mm can mean the difference between a successful nerve block and a failure.
Gruber and Bodner have shown that sonographically guided pudendal nerve block can be successful in the right hands. We believe that the procedure for CT-guided nerve blocks, in which the location of the needle is verified by a small test injection of diluted contrast material is more easily learned and performed by a larger number of practicing radiologists than would be the case for a sonographically guided procedure, and it provides a high degree of clinical success.
References
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