Anatomy and neurophysiology of antegrade ejaculation

Normal antegrade ejaculation is the coordinated physiologic process involving sequential phases of seminal emission and bladder neck closure followed by expulsion of semen by rhythmic contraction of the bulbocavernosus and ischiocavernosus muscles. The emission phase is under autonomic sympathetic control with afferent impulses transmitted via the pudendal nerve. Efferent impulses originate in the preganglionic fibers from T10 to L2, synapse in the ganglia of the lumbar sympathetic trunks, and exit via L1 to L4 postganglionic fibers, which decussate along the aorta bilaterally to form the hypogastric plexus. Terminal nerves from the pelvic plexus evoke seminal emission innervating the seminal vesicles, vas deferens, prostate, and bladder neck. From the surgeon's perspective, identification and careful preservation of the lumbar sympathetic trunks, the postganglionic fibers particularly at the L2 to L4 level, and the nerves of the hypogastric plexus are the objectives of the nerve-sparing approach. Dieckmann and colleagues [17] described an intraoperative test for identifying relevant lumbar sympathetic nerve fibers using direct electrostimu-lation. During open RPL, electrostimulation was applied to L1 to L3 sympathetic fibers while intraoperative ejaculation was observed and reproduced. These studies identified the predominance of the right-sided nerves, which are usually more prominent and easily preserved.

Anatomically, the sympathetic trunks are chains of interconnected ganglia that course between the medial aspect of the psoas major and the vertebral column in the retroperitoneum. The right sympathetic chain is situated posterior to the middle of the inferior vena cava (IVC) and the left chain is located posterolateral to the abdominal aorta with transverse rami connecting the two trunks. While they appear asymmetric to the great vessels, they are aligned with the embryonic vascular tree before regression of the left-sided venous system. Similarly, the lymphatic drainage of the testes appears asymmetric in the adult, but in both cases, if one considers the midline as the aorta, the sympathetic system as well as the vascular and lymphatic anatomy is "similar" bilaterally. The sympathetic chains are often intimately involved with lumbar vessels and the number, size, and position of paravertebral ganglia are variable. Colleselli and colleagues [18] demonstrated in a cadaver anatomical study that the L2 and L3 ganglia are close to each other and often fused. Anterior to the aortic bifurcation and extending inferiorly on the anterior surface of the fifth lumbar vertebra is the superior hypogastric plexus, which is contiguous with the inferior hypogastric plexus and pelvic plexuses connected by the right and left hypogastric nerves, which are readily identified. It is less clear if significant nerves course to the inferior plexus along the inferior mesenteric artery, which may be skeletonized or divided during lymphadenectomy.

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