The pelvic neuroanatomy
As described in our video articles published in 2015 in Fertility and Sterility6 and 2019 in the Journal of Minimally Invasive Gynecology,5 the left and right hypogastric nerves are the main sympathetic nerves of the autonomic nervous system in the pelvis. They originate from the superior hypogastric plexus and, at the level of the middle rectal vessels, they join the pelvic sacral splanchnic nerves to form the inferior hypogastric plexus. They are easily identifiable at their origin and are the most superficial and readily identifiable component of the inferior hypogastric plexus.
Courtesy Dr. Meghan McGrattan
Fig. 1: Pelvic neuroanatomy
The sympathetic input from the hypogastric nerves causes the internal urethral and anal sphincters to contract, as well as detrusor relaxation and a reduction of peristalsis of the descending colon, sigmoid, and rectum; thus, hypogastric nerve input promotes continence.
The hypogastric nerves also carry afferent signals for pelvic visceral proprioception. Lesion to the hypogastric nerves will usually be subclinical and will put the patient at risk for unnoticeable bladder distension, which usually becomes symptomatic about 7 years after the procedure.7
Courtesy Dr. Meghan McGrattan
Fig. 2: Pelvic neuroanatomy
The thin pelvic splanchnic nerves – which merge with the hypogastric nerves into the pararectal fossae to form the inferior hypogastric plexus – arise from nerve roots S2 and S4 and carry all parasympathetic signals to the bladder, rectum, and the sigmoid and left colons. Lesions to these bundles are the main cause of neurogenic urinary retention.
The inferior hypogastric plexi split into the vesical, uterine, and rectal branches, which carry the sympathetic, parasympathetic, and sensory fibers from both the splanchnic and hypogastric nerves. Damage to the inferior hypogastric plexi and/or its branches may induce severe dysfunction to the target organs of the injured fibers.
A focus on the hypogastric nerve
Our approach was developed after we studied the anatomic reliability of the hypogastric nerves through a prospective observational study consisting of measurements during five cadaveric dissections and 10 in-vivo laparoscopic surgeries for rectosigmoid endometriosis.4 We took an interfascial approach to dissection.
Our goal was to clarify the distances between the hypogastric nerves and the ureters, the midsagittal plane, the midcervical plane, and the uterosacral ligaments in each hemipelvis, and in doing so, enable identification of the hypogastric nerves and establish recognizable limits for dissection.
We found quite a bit of variance in the anatomic position and appearance of the hypogastric nerves, but the variances were not very broad. Most notably, the right hypogastric nerve was significantly farther toward the ureter (mean, 14.5 mm; range, 10-25 mm) than the left one (mean, 8.6 mm; range, 7-12 mm).
The ureters were a good landmark for identification of the hypogastric nerves because the nerves were consistently found medially and posteriorly to the ureter at a mean distance of 11.6 mm. Overall, we demonstrated reproducibility in the identification and dissection of the hypogastric nerves using recognizable interfascial planes and anatomic landmarks.4
With good anatomic understanding, a stepwise approach can be taken to identify and preserve the hypogastric nerve and the deeper inferior hypogastric plexus without the need for more extensive dissection.
As shown in our 2019 video, the right hypogastric nerves can be identified transperitoneally in most cases.5 For confirmation, a gentle anterior pulling on the hypogastric nerve causes a caudal movement of the peritoneum overlying the superior hypogastric plexus. (Intermittent pulling on the nerve can also be helpful in localizing the left hypogastric nerve.)
To dissect a hypogastric nerve, the retroperitoneum is opened at the level of the pelvic brim, just inferomedially to the external iliac vessels, and the incision is extended anteriorly, with gentle dissection of the underlying tissue until the ureter is identified.
Once the ureter is identified and lateralized, dissection along the peritoneum is carried deeper and medially into the pelvis until the hypogastric nerve is identified. Lateral to this area are the internal iliac artery, the branching uterine artery, and the obliterated umbilical ligament. In the left hemipelvis, the hypogastric nerve can reliably be found at a mean distance of 8.6 mm from the ureter, while the right one will be found on average 14.5 mm away.
The hypogastric nerves form the posteromedial limit for a safe and simple nerve-sparing dissection. Any dissection posteriorly and laterally to these landmarks should start with the identification of sacral nerve roots and hypogastric nerves.
Dr. Lemos reported that he has no relevant disclosures.
Dr. Lemos is associate professor in the department of obstetrics and gynecology at the University of Toronto.
References
1. Imboden S et al. J Minim Invasive Gynecol. 2021 Aug;28(8):1544-51. doi: 10.1016/j.jmig.2021.01.009.
2. Possover M et al. J Am Coll Surg. 2005;201(6):913-7. doi: 10.1016/j.jamcollsurg.2005.07.006.
3. Ceccaroni M et al. Surg Endosc. 2012;26(7):2029-45. doi: 10.1007/s00464-012-2153-3.
4. Seracchioli R et al. J Minim Invasive Gynecol. 2019;26(7):1340-5. doi: 10.1016/j.jmig.2019.01.010.
5. Zakhari A et al. J Minim Invasive Gynecol. 2020;27(4):813-4. doi: 10.1016/j.jmig.2019.08.001
6. Lemos N et al. Fertil Steril. 2015 Nov;104(5):e11-2. doi: 10.1016/j.fertnstert.2015.07.1138.
7. Possover M. Fertil Steril. 2014 Mar;101(3):754-8. doi: 10.1016/j.fertnstert.2013.12.019.