A step towards stereotactic navigation during pelvic surgery: 3D nerve topography

Abstract

Background: Long-term morbidity after multimodal treatment for rectal cancer is suggested to be mainly made up by nerve-injury-related dysfunctions. Stereotactic navigation for rectal surgery was shown to be feasible and will be facilitated by highlighting structures at risk of iatrogenic damage. The aim of this study was to investigate the ability to make a 3D map of the pelvic nerves with magnetic resonance imaging (MRI).

Methods: A systematic review was performed to identify a main positional reference for each pelvic nerve and plexus. The nerves were manually delineated in 20 volunteers who were scanned with a 3-T MRI. The nerve identifiability rate and the likelihood of nerve identification correctness were determined.

Results: The analysis included 61 studies on pelvic nerve anatomy. A main positional reference was defined for each nerve. On MRI, the sacral nerves, the lumbosacral plexus, and the obturator nerve could be identified bilaterally in all volunteers. The sympathetic trunk could be identified in 19 of 20 volunteers bilaterally (95%). The superior hypogastric plexus, the hypogastric nerve, and the inferior hypogastric plexus could be identified bilaterally in 14 (70%), 16 (80%), and 14 (70%) of the 20 volunteers, respectively. The pudendal nerve could be identified in 17 (85%) volunteers on the right side and in 13 (65%) volunteers on the left side. The levator ani nerve could be identified in only a few volunteers. Except for the levator ani nerve, the radiologist and the anatomist agreed that the delineated nerve depicted the correct nerve in 100% of the cases.

Conclusion: Pelvic nerves at risk of injury are usually visible on high-resolution MRI with dedicated scanning protocols. A specific knowledge of their course and its application in stereotactic navigation is suggested to improve quality of life by decreasing the likelihood of nerve injury.

Keywords: Anatomy; Autonomic nervous system; Hypogastric plexus; Magnetic resonance imaging; Medical; Neuronavigation; Topography.

Fig. 1

3D MRI pelvic nerve topography showing the anatomical relationships between the pelvic nerves and the pelvic organs in a male (A) and in a female volunteer (B). A video of such a delineation is available as supplementary material 1. The following pelvic organs and nerves can be distinguished: bladder/ureter and urethra (orange), mesorectum of the low and partially mid-rectum (green), prostate/seminal vesicles/deferent duct (in A, blue), sacrum and partially iliac bone (in A, gray), uterus/vagina/round ligament (in B, gray), ovaria (purple), SNs/lumbosacral plexus/PN/LAN (yellow), ST (turquoise, running ventrally along the sacrum), ON (turquoise, the most ventrally situated nerve), SHP/HN (pink), IHP (in A, white/distal side pink; in B the pink HN is running through in the IHP). (Color figure online)

Fig. 2

Different orientations showing the spatial relationship between the pelvic nerves in a male volunteer. A is an anteroposterior view slightly from the side. In B, the type of view is the same without the IHP (white) to show the PSNs, also known as the erigent pillar transferring parasympathetic fibers from the sacral nerves to the IHP. C, D illustrate a pure anteroposterior view such as encountered during, for example, a transanal total mesorectal excision and a view similar to what one would have during a laparoscopic total mesorectal excision, respectively. The following structures can be distinguished: ureter (orange), SNs/lumbosacral plexus/PN/LAN (yellow), ST (green), ON (turquoise), SHP/HN (pink), IHP (in A/C/D, white/distal side pink). (Color figure online)

Fig. 3

Three images in the sagittal orientation without (A, C, E) and with nerve segmentation (B, D, F) of the SNs (yellow), ST (green), HN (pink) joining the IHP (white). The infralevatory PN is delineated (yellow). The HN and IHP can best be discerned by sagittal navigation. (Color figure online)