Residency · Residency · General Surgery
Surgical Anatomy of the Autonomic Nervous System in the Abdomen and Pelvis
Introduction
The autonomic nervous system (ANS) in the abdomen and pelvis controls gastrointestinal motility, sphincter function, bladder function, and sexual function. Iatrogenic injury to these nerves during surgery can cause devastating functional deficits including gastroparesis, diarrhea, urinary retention, and sexual dysfunction. The general surgeon must possess thorough knowledge of autonomic anatomy to avoid nerve injury during retroperitoneal dissection, lymphadenectomy, pelvic surgery, and vascular procedures.
Overview of the Autonomic Nervous System
The sympathetic nervous system has a thoracolumbar outflow from T1 to L2/3, with preganglionic neurons in the intermediolateral cell column of the spinal cord that synapse in paravertebral ganglia (the sympathetic chain) or prevertebral ganglia (celiac, superior mesenteric, and inferior mesenteric). The parasympathetic nervous system has a craniosacral outflow, with the cranial component provided by the vagus nerve (CN X) supplying the foregut and midgut, and the sacral component provided by the pelvic splanchnic nerves from S2 to S4 supplying the hindgut, bladder, and reproductive organs. The enteric nervous system is the intrinsic nervous system of the GI tract, consisting of the Auerbach (myenteric) plexus between the circular and longitudinal muscle layers and the Meissner (submucosal) plexus. It is capable of autonomous function but is modulated by sympathetic and parasympathetic input.
Sympathetic Anatomy in the Abdomen
Sympathetic Chain (Paravertebral Ganglia)
The sympathetic chains are paired structures running along the anterolateral surface of the vertebral bodies, lying posterior to the aorta on the left and the IVC on the right. The greater splanchnic nerve, carrying fibers from T5 to T9, pierces the crus of the diaphragm and synapses in the celiac ganglion. The lesser splanchnic nerve from T10 to T11 synapses in the aorticorenal ganglion. The least splanchnic nerve from T12 synapses in the renal plexus. The lumbar splanchnic nerves from L1 to L4 contribute to the inferior mesenteric plexus and superior hypogastric plexus. The sympathetic chain may be injured during retroperitoneal lymph node dissection (RPLND), aortic surgery, and posterior approach to the spine.
Prevertebral (Preaortic) Ganglia and Plexuses
The celiac plexus and ganglion surround the origin of the celiac trunk at the level of T12 to L1, receiving the greater and lesser splanchnic nerves and vagal fibers. It distributes to the foregut organs: stomach, liver, spleen, pancreas, and proximal duodenum. The superior mesenteric plexus and ganglion surround the SMA origin and supply the midgut from the distal duodenum to the splenic flexure. The inferior mesenteric plexus surrounds the IMA origin, supplies the hindgut from the descending colon to the upper rectum, and gives rise to the superior hypogastric plexus. The intermesenteric plexus (aortic plexus) connects the SMA and IMA plexuses along the anterior aorta and is at risk during aortic surgery and retroperitoneal lymphadenectomy.
<image>Anterior view of the retroperitoneum showing the sympathetic chains, splanchnic nerves, prevertebral ganglia and plexuses (celiac, superior mesenteric, inferior mesenteric, intermesenteric/aortic), the superior hypogastric plexus at the aortic bifurcation, and the hypogastric nerves descending into the pelvis, with the aorta and IVC shown as translucent landmarks</image>
Parasympathetic Anatomy in the Abdomen
Vagus Nerve (CN X)
The right vagus primarily forms the posterior vagal trunk, lying posterior to the esophagus. It gives off the celiac branch, which is its largest branch and supplies the celiac plexus, and continues as the posterior gastric nerve. The left vagus primarily forms the anterior vagal trunk, lying anterior to the esophagus. It gives off the hepatic branch, which runs in the lesser omentum to the liver and biliary system, and continues as the anterior gastric nerve, also known as the nerve of Latarjet. The criminal nerve of Grassi is the first branch of the posterior vagal trunk to the gastric fundus; failure to divide this nerve during vagotomy leads to recurrent ulcer disease. Knowledge of vagal anatomy is essential for truncal vagotomy, highly selective vagotomy (parietal cell vagotomy), hiatal hernia repair, esophagectomy, and fundoplication.
Pelvic Splanchnic Nerves (Nervi Erigentes)
The pelvic splanchnic nerves arise from the S2, S3, and S4 ventral rami and provide parasympathetic innervation to the hindgut (descending colon, sigmoid, and rectum), bladder, and reproductive organs. They join the inferior hypogastric (pelvic) plexus on the lateral pelvic wall. Their functions include bladder detrusor contraction, rectal motility, and erectile function via the cavernous nerves. They are at greatest risk during low anterior resection, abdominoperineal resection, radical hysterectomy, and lateral pelvic dissection.
Pelvic Autonomic Anatomy
Superior Hypogastric Plexus
The superior hypogastric plexus is located at the aortic bifurcation and sacral promontory, anterior to the L5-S1 vertebral bodies. It contains predominantly sympathetic fibers from the lumbar splanchnic nerves and intermesenteric plexus and divides into the left and right hypogastric nerves. Sympathetic functions in the pelvis include bladder neck contraction (maintaining continence), internal anal sphincter tone, ejaculation (through vas deferens and seminal vesicle contraction), and uterine contraction. This plexus is at surgical risk during high ligation of the IMA, presacral dissection, and retroperitoneal lymphadenectomy.
Hypogastric Nerves
The hypogastric nerves are paired structures descending from the superior hypogastric plexus into the pelvis along the lateral pelvic sidewall. They run in the retroperitoneal tissue posterior to the ureter and join the inferior hypogastric (pelvic) plexus on the lateral wall of the rectum.
Inferior Hypogastric (Pelvic) Plexus
The inferior hypogastric plexus is located on the lateral pelvic sidewall at the level of the rectum, positioned posterior and lateral to the seminal vesicles in males or the uterosacral ligaments in females. It receives input from the hypogastric nerves (sympathetic) and pelvic splanchnic nerves (parasympathetic) and gives off branches to the bladder, prostate or uterus, rectum, and external genitalia. The cavernous nerves of Walsh arise from this plexus and travel along the posterolateral prostate to innervate the corpora cavernosa; they are critical for erectile function and are at risk during radical prostatectomy and low rectal surgery.
<image>Sagittal section of the male pelvis showing the autonomic nerve pathways: superior hypogastric plexus at the sacral promontory, hypogastric nerves descending along the pelvic sidewall, inferior hypogastric plexus lateral to the rectum, pelvic splanchnic nerves (S2-S4) joining the plexus, and the cavernous nerves of Walsh passing along the posterolateral prostate, with labeled danger zones during rectal and prostate surgery</image>
Nerve-Sparing Surgical Techniques
During Colorectal Surgery
During high IMA ligation, the surgeon should dissect anterior to the aorta and identify the superior hypogastric plexus before dividing the IMA, ligating it distal to the left colic artery when oncologically appropriate. During presacral dissection, the correct surgical plane is the areolar plane between the mesorectal fascia (fascia propria of the rectum) and the presacral fascia (Waldeyer's fascia); staying in this plane preserves the hypogastric nerves. During lateral dissection, it is essential to avoid dissecting lateral to the mesorectum below the peritoneal reflection, as the inferior hypogastric plexus lies on the lateral pelvic sidewall. During anterior dissection, Denonvilliers' fascia separates the rectum from the prostate and seminal vesicles, and staying on the rectal side preserves the cavernous nerves.
During Retroperitoneal Lymph Node Dissection (RPLND)
Modified template dissection limits the dissection to one side of the aorta based on tumor laterality, preserving contralateral sympathetic fibers responsible for ejaculation. The nerve-sparing technique identifies and preserves the postganglionic sympathetic fibers from L1 to L3 that cross anterior to the aorta to form the superior hypogastric plexus. This approach preserves antegrade ejaculation in over 95% of patients undergoing modified template nerve-sparing RPLND.
During Aortic Surgery
Excessive dissection of periaortic tissue at the aortic bifurcation and left common iliac artery should be avoided. Preserving the superior hypogastric plexus prevents retrograde ejaculation. A lateral approach to the aorta reduces nerve injury risk compared to an anterior approach.
Clinical Consequences of Autonomic Nerve Injury
Injury to the superior hypogastric plexus most commonly causes retrograde ejaculation and may also cause bladder dysfunction. Hypogastric nerve injury leads to urinary retention, loss of ejaculation, and uterine atony. Pelvic splanchnic nerve injury causes bladder atony with inability to void, erectile dysfunction, and loss of rectal sensation. Vagus nerve injury can result in dumping syndrome, diarrhea, and gastroparesis if bilateral truncal vagotomy is performed without a drainage procedure. Celiac plexus disruption may cause postgastrectomy diarrhea and pancreatic exocrine insufficiency.
Clinical Pearls
The superior hypogastric plexus lies at the aortic bifurcation and sacral promontory and is at risk during high IMA ligation and presacral dissection. Total mesorectal excision performed in the correct avascular plane between the mesorectal fascia and presacral fascia preserves the hypogastric nerves. The pelvic splanchnic nerves from S2 to S4 are responsible for bladder emptying and erectile function and are at greatest risk during lateral pelvic dissection. Nerve-sparing RPLND preserves antegrade ejaculation in over 95% of patients by identifying and protecting the postganglionic sympathetic fibers. Understanding autonomic anatomy transforms these nerves from invisible structures into identifiable landmarks that can be systematically preserved.
References
- Lange MM, Marijnen CA, Maas CP, et al. Risk factors for sexual dysfunction after rectal cancer treatment. Eur J Cancer. 2009;45(9):1578-1588.
- Havenga K, Enker WE, McDermott K, et al. Male and female sexual and urinary function after total mesorectal excision with autonomic nerve preservation for carcinoma of the rectum. J Am Coll Surg. 1996;182(6):495-502.
- Donohue JP, Thornhill JA, Foster RS, et al. Retroperitoneal lymphadenectomy for clinical stage A testis cancer (1965 to 1989): modifications of technique and impact on ejaculation. J Urol. 1993;149(2):237-243.
- Skandalakis JE, Colborn GL, Weidman TA, et al. Skandalakis' Surgical Anatomy. Chapter on Autonomic Nervous System. McGraw-Hill; 2004.
