Ultrasound-guided ganglion impar (Walther) block is utilized in a variety of clinical scenarios as a diagnostic, prognostic, and therapeutic maneuver. As a diagnostic tool, ultrasound-guided ganglion impar (Walther) block allows accurate placement of the needle tip within proximity of the ganglion impar when performing differential neural blockade on an anatomic basis in the evaluation of pelvic, bladder, perineal, genital, rectal, and anal pain. As a prognostic tool, ultrasound-guided ganglion impar block can be utilized as a prognostic indicator of the degree of motor and sensory impairment that the patient may experience if the ganglion impar is going to be destroyed in an effort to palliate intractable pain. In the acute pain setting, ultrasound-guided ganglion impar (Walther) block with local anesthetics and/or steroids may be used to palliate acute pain emergencies while waiting for pharmacologic, surgical, and/or antiblastic methods to become effective. This technique has great clinical utility in both children and adults when managing acute postoperative and posttrauma pain. Sympathetically mediated pain syndromes including the pain of acute herpes zoster of the lower sacral and coccygeal dermatomes can also be effectively managed with epidurally administered local anesthetics, steroids, and/or opioids. Additionally, this technique is of value in patients suffering from pain secondary to endometriosis, reflex sympathetic dystrophy, causalgia, proctitis fugax, and radiation enteritis.

Pain of malignant origin involving the pelvis, perineum, rectum, anus, genitals, and lower extremities is also amenable to treatment with local anesthetics and steroids administered by this technique.

The five sacral vertebrae are fused together to form the triangular-shaped sacrum (Fig. 130.1). The dorsally convex sacrum inserts in a wedge-like manner between the two iliac bones with superior articulations with the fifth lumbar vertebra and caudad articulations with the coccyx. On the anterior concave surface, there are four pairs of unsealed anterior sacral foramina that allow passage of the anterior rami of the upper four sacral nerves. The posterior sacral foramina are smaller than their anterior counterparts. Leakage of drugs injected into the sacral canal is effectively prevented by the sacrospinal and multifidus muscles. The vestigial bony remnants that are the result of the incomplete fusion of the inferior articular processes of the lower half of the S4 and all of the S5 vertebrae project downward on each side of the sacral hiatus (see Fig. 130.1). These bony projections are called the sacral cornua and represent important clinical landmarks when performing ultrasound-guided ganglion impar (Walther) nerve block. The U-shaped sacral hiatus is covered posteriorly by the sacrococcygeal ligament, which is also an important clinical landmark when performing ultrasound ganglion impar (Walther) nerve block (Fig. 130.2). Penetration of the sacrococcygeal joint provides direct access to precoccygeal space. The ganglion of impar (Walther) lies in front of the sacrococcygeal joint and is amenable to blockade at this level (Fig. 130.3). The ganglion receives fibers from the lumbar and sacral portions of the sympathetic and parasympathetic nervous system and provides sympathetic innervation to portions of the pelvic viscera and genitalia (Fig. 130.4). Although there are gender- and race-determined differences in the shape of the sacrum, they are of little importance relative to the ultimate ability to successfully perform ganglion impar (Walther) nerve block on a given patient. The triangular coccyx is made up of three to five rudimental vertebrae. Its superior surface articulates with the inferior articular surface of the sacrum.

Ultrasound-guided ganglion impar (Walther) block can be carried out by placing the patient in the prone position with the patient’s abdomen resting on a thin pillow (Fig. 130.5). To relax the gluteal muscles, the patient is asked to turn his or her heels outward (Fig. 130.6). A total of 6 mL of local anesthetic suitable for epidural administration is drawn up in a 20-mL sterile syringe. If the painful condition being treated is thought to have an inflammatory component, 40 to 80 mg of depot steroid is added to the local anesthetic. The skin overlying the sacrum, sacral hiatus, and coccyx is then prepped with antiseptic solution, and the sacral hiatus and cornua are palpated using a rocking motion (Fig. 130.7). A high-frequency linear ultrasound transducer is then placed over the lower sacrum

in the transverse plane and slowly moved caudally until the sacral cornua are visualized (Figs. 130.8 and 130.9). The classic ultrasound appearance of the sacral cornua and their acoustic shadow are reminiscent of two nuns walking down the street (Fig. 130.10). Lying between the two nuns is the sacral hiatus, which provides access to the epidural space (see Fig. 130.11). Between the necks of the two is the sacrococcygeal ligament, which appears as a hyperechoic band-like

structure (Fig. 130.11). Lying just beneath the sacrococcygeal ligament is the hypoechoic caudal canal (see Fig. 130.11). The floor of the caudal canal will appear as a bright hyperechoic line (see Fig. 130.11).