Accuracy of Ultrasound-Guided Pudendal Nerve Block in the Ischial Spine and Alcock’s Canal Levels: A Cadaveric Study

Background Blockade of the pudendal nerve (PN) using ultrasound (US) guidance has been described at the levels of the ischial spine and Alcock’s canal. However, no study has been conducted to compare anatomical accuracy between different approaches in targeting the PN. Objective To investigate the accuracy of US-guided injection of the PN at the ischial spine and Alcock’s canal levels. This study also compared the accuracy of the infiltrations by three sonographers with different levels of experience. Subjects Eight Thiel-embalmed cadavers (16 hemipelvises). Methods Three physiatrists trained in musculoskeletal US imaging with 12 years, five years, and one year of experience performed the injections. Each injected a 0.1-mL bolus of colored dye in both hemipelvises of each cadaver at the ischial spine and Alcock’s canal levels under US guidance. Each cadaver received three injections per hemipelvis. The accuracy of the injection was determined following hemipelvis dissection by an anatomist. Results The injections were accurate 33 times out of the total 42 attempts, resulting in 78% accuracy. Sixteen out of 21 injections at the ischial spine level were on target (76% accuracy), while the approach at Alcock’s canal level yielded 17 successful injections (81% accuracy). The difference between the approaches was not statistically significant. There was also no significant difference in accuracy between the operators. Conclusions US-guided injection of the PN can be performed accurately at both the ischial spine and Alcock’s canal levels. The difference between the approaches was not statistically significant.

Urological eponyms

Alcock’s canal: canal for the internal pudendal vessels and nerve in the ischiorectal fossa. Benjamin Alcock (b 1801). Professor of Anatomy, Physiology, and Pathology (1837) at the Apothecaries Hall in Dublin. Anderson–Hynes pyeloplasty: dismembered pyeloplasty for PUJO. James Anderson and Wilfred Hynes. Surgeons, Sheffield United Hospitals....

CT-Guided Percutaneous Infiltration for the Treatment of Alcock’s Neuralgia

The pudendal nerve may be strained either between the sacrospinous and sacrotuberous ligaments at the ischial spine level or within Alcock’s canal. Alcock’s neuralgia is a rare, painful condition caused by compression of the pudendal nerve within Alcock’s canal (pudendal canal) which is an aponeurotic tunnel that cannot be stretched. Patients usually present with intense, unilateral pain involving anatomic areas along the pudendal nerve’s root, genital, anal, and pelvic regions causing mobility impairment. A computed tomography (CT) - guided percutaneous infiltration of the pudendal nerve with a mixture of a local anesthetic and a long-acting corticosteroid is a safe and efficient method that reduces the pain caused by the neuralgia. Corticosteroids and local anesthetics interfere with the neurons, the encoding, and the processing of noxious stimuli; interrupt the pain-spasm cycle; and reduce inflammation. The injected glucocorticosteroid may take 3-5 days to reach its anti-inflammatory effect; therefore, the initial pain relief from the local anesthetic is followed by a baseline pain return and then secondary pain relief at 3-5 days. The procedure is performed under minimal or no anesthesia. In general, at discharge, a responsible person must accompany the patient and ensure a safe return home. Clinical evaluation is performed after 7-10 days. There are 2 types of potential complications that are associated with percutaneous steroid infiltrations: intra-operative (associated with needle placement) and post-operative (infection, bleeding and those associated with the injectate administration). In all cases that steroids were administered within therapeutic doses, no complications were noted. In conclusion, CT-guided percutaneous infiltration with a mixture of long-acting corticosteroid and local anesthetic seems to be a safe and efficient method for the treatment of Alcock’s neuralgia. Key words: Alcock’s canal, neuralgia, corticosteroid, pudendal; nerve, local anesthetic, computed tomography, infiltration, percutaneous, image guided.