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Brown: Atlas of Regional Anesthesia, 3rd ed., Copyright © 2006 Saunders, An Imprint of Elsevier
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PLACEMENT

Anatomy.

The superior hypogastric plexus is continuous with the intermesenteric plexus and is located retroperitoneally, caudad to the origin of the inferior mesenteric artery. It lies anterior to the lower part of the abdominal aorta, its bifurcation, and the middle sacral vessels; more specifically, it is anterior to the fourth and fifth lumbar vertebrae and the first sacral vertebra. The plexus is composed of a flattened band of intercommunicating nerve bundles that descend over the aortic bifurcation ( Figs. 43-1 and 43–2 ). Broadening below, it divides into right and left hypogastric nerves. In addition to its continuity with the intermesenteric plexus, the superior hypogastric plexus receives input from the lower two lumbar splanchnic nerves ( Fig. 43-3 ). Fig. 43-3 identifies, with a red triangle, a key concept in the superior hypogastric plexus nerve block. The red triangle highlights the anatomic window that exists between the iliac crest, the L5 transverse process, and the L5–S1 vertebral bodies, which allows successful needle insertion.

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Figure 43-1  Anteroposterior anatomy of the superior hypogastric plexus.


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Figure 43-2  A–C, Cross-sectional anatomy of the superior hypogastric plexus.


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Figure 43-3  Oblique anatomy of the superior hypogastric plexus. A, Anatomy. B, Concept of the “red triangle” for access to the superior hypogastric plexus.


In addition to sympathetic fibers, the superior hypogastric plexus usually also contains parasympathetic fibers that originate in the ventral roots of S2–4 and travel as slender nervi erigentes (pelvic splanchnic nerves) through the inferior hypogastric plexus.

The left and right hypogastric nerves descend lateral to the sigmoid colon and rectosigmoid junction to reach the two inferior hypogastric plexuses. The inferior hypogastric plexus is a bilateral structure situated on either side of the rectum, the lower portion of the bladder, and the prostate and seminal vesicles (in males) or the uterine cervix and vaginal fornices (in females). Because of its location and configuration, the inferior hypogastric plexus does not lend itself to neurolysis.

Position.

Patients undergoing superior hypogastric plexus block are placed prone on a radiographic imaging table with a pillow underneath the lower abdomen to reduce lumbar lordosis. Ideally, biplane fluoroscopy is available to assess needle placement, for which oblique posteroanterior and lateral images are needed.

Needle Puncture.

The L4–5 interspace is identified fluoroscopically, and skin marks are placed 5 to 7 cm lateral to the midline at the level of the L4–5 interspace ( Fig. 43-4 ). This preparation is needed for the insertion of needles through the area of bony access (shown by the red triangle in Figs. 43-3 , 43–4 , 43–5 ) to the superior hypogastric plexus. After aseptic skin preparation, skin infiltration with local anesthetic is performed with a 30-gauge, 2-cm needle at the previously marked bilateral sites. Then local anesthetic infiltration is continued subcutaneously with a 22-gauge, 5- to 9-cm needle along the eventual caudomedially directed, oblique needle path. The fluoroscopic beam is directed along the projected needle path to simplify needle insertion. The needle is then directed under fluoroscopic guidance to reach a point immediately anterior to the L5–S1 vertebral junction; the fluoroscopic beam is directed to minimize the needle hub’s radiographic size. If the fluoroscopic beam is directed properly, this approach should guide the needle tip to the correct position. The iliac crest and the L5 transverse process may obstruct passage of the needle; if this is the case, the needle is withdrawn and redirected in a cephalad or caudad angle to bypass the obstruction ( Fig. 43-5 ). As with the approach taken with either the celiac or lumbar sympathetic block, if the needle tip contacts the body of the vertebra (in this case L5), the needle is simply redirected to “walk off” the body to its desired position immediately anterior to the L5–S1 junction (the sacral prominence).

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Figure 43-4  Surface anatomy and skin markings important for superior hypogastric plexus block: posteroanterior view.


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Figure 43-5  Technique for superior hypogastric plexus block using the “red triangle” to identify the route of needle insertion and access to the superior hypogastric plexus. A, Anteroposterior view. B, Cross section. C, Posterior oblique view.


Once the needle tip is positioned adequately, and the position has been confirmed with biplanar fluoroscopy, the contralateral needle is inserted in a similar manner. Once both needles are positioned, radiocontrast medium (2–4 mL of Hypaque M-60) is injected to verify adequate placement. The radiocontrast agent should spread in a band immediately anterior to the sacral promontory; its smooth posterior margin should identify needle tip placement anterior to the psoas fascia. The contrast should spread toward the midline from the bilaterally placed paramedian sites.

Potential Problems.

Owing to the proximity of the iliac vessels (arteries and veins) to the needle paths, care is taken to minimize the potential for intravascular injection ( Fig. 43-6 ). This anatomic relation also makes hematoma formation possible. If the position of the needle tip is not verified, both intramuscular and intraperitoneal injection are possible. Even when the needle is inserted correctly, paraspinous muscle spasm may result owing to needle-induced paraspinous muscle irritation. This usually lasts only a few days. Less frequent problems are lumbar or sacral somatic nerve injury and renal or ureteral puncture. It is advisable to caution the patient about the potential for bowel or bladder habit changes as well as decreased sexual function following the neurolytic superior hypogastric plexus block despite the rarity of these side effects.

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Figure 43-6  Anatomy as seen by magnetic resonance imaging of the superior hypogastric plexus.


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