Comparison of Ultrasound-guided Transgluteal and Finger-guided Transvaginal Pudendal Nerve Block Techniques: Which One is More Effective?

Pudendal neuralgia (PN) is a painful neuropathic condition for which current prevalence is unknown due to often going under-recognized by gynecologists. Pudendal neuralgia typically presents as unilateral severe sharp and burning pain, numbness, or paranesthesia on the anatomic pathways of the pudendal nerve. The most common causes for PN include pudendal nerve injury during vaginal procedures, stretching and compression of the pudendal nerve during vaginal delivery, and prolonged sitting position.

As in many neuropathic syndromes, there is currently no gold standard diagnostic test for assessing PN. In 2006, the Nantes criteria were described by a multidisciplinary working party to describe the clinical diagnostic criteria, and a standard approach was created for PN diagnosis. According to the Nantes criteria, patients should fulfil all five essential criteria without meeting any of the exclusion criteria. The five essential diagnostic criteria were defined as, 1: pain in the anatomic territory of the pudendal nerve, 2: that is worsened by sitting, 3: the patient is not woken at night by the pain, 4: no objective sensory loss on clinical examination, and 5: positive anesthetic pudendal nerve block.

Pudendal nerve infiltration (PNI), which was defined as an essential step, is performed for diagnostic purposes and as an important treatment modality in patients with PN. This approach aims for long-term relief of pain, as in all forms of nerve entrapment syndromes, by treating a possible inflammatory component, it also provides neuroprotection to the central nervous system and reduces spontaneous ectopic activity of the affected nerve.

Image-guided or finger-guided PNIs can be performed according to the experience of the physician, adequate equipment presence, and patient choice. The pudendal nerve is situated in the deepest area in the pelvis and it makes the PNI technically difficult if transperineal or transgluteal approaches are preferred. For this reason, it usually requires imaging guidance to target the injection site such as ultrasound, computed tomography, fluoroscopy, and magnetic resonance.

Ultrasound-guided transgluteal (TG) PNI has been described to reach the pudendal nerve in the plane between the sacrotuberous and sacrospinous ligaments. This technique has many advantages such as visualization of the substantial structures (pudendal artery and the sciatic nerve) without radiation exposure it enables real-time images. However, finger-guided transvaginal (TV) PNI should be kept in mind as a PNI option with the advantages of familiarity for gynecologists and obstetricians as an essential part of obstetric anesthesia. Finger-guided blocks in women are easily performed via a vaginal approach by palpation the ischial spines and the injection is targeted slightly medially and posteriorly to the ischial spines.