Intraoperative Neuromonitoring of Pelvic Autonomous Nerve Plexus During Total Mesorectal Excision

The introduction of Total Mesorectal Excision (TME) resulted to the improvement of the overall survival and local recurrence rates of rectal cancer patients. However, the associated urogenital and anorectal functional deficit has a significant effect on the postoperative quality of life of the patient. More specifically, the postoperative rates of urogenital and sexual dysfunction that have been reported in the various series, are estimated at the levels of 70% and 90%, respectively. Additionally, TME is associated with the development of the low anterior syndrome (LARS). LARS is characterized by the onset of fecal incontinence, due to injury in the autonomic nerve plexuses that innervate the internal anal sphincter (IAS); who in turn is responsible for the 52-85% anal resting tone. According to a recent study, 38.8% and 33.7% of patients with normal preoperative urogenital function, developed postoperative stool and urine incontinence, respectively.

It becomes apparent that the incidence rates of these complications vary between the various series, mainly due to their small sample size, the lack of comparative data, the short follow up period, the use of non-validated tools and their retrospective design. Several predictive factors of these adverse events have been suggested in the literature, including old age, tumors located less than 12 cm from the anal verge, preoperative radiotherapy and injury to the pelvic autonomous nerves.

The clinical and functional anatomy of the pelvis are quite complex. The inferior hypogastric plexus is formed by the parasympathetic pelvic nerves, deriving from the I2-I4 and the sympathetic hypogastric nerve. It is a neural anatomic structure that carries organ-specific nerve fibers. Visual identification of the plexus is quite difficult, for various reasons, including the complexity of the nerve distribution, the narrow pelvis, the voluminous mesorectum, obesity, previous pelvic operations, neoadjuvant radiotherapy, locally advanced tumors, intraoperative bleeding and the extensive use of diathermy. According to the current literature, identification of the autonomous pelvic plexus is achievable in 72% of cases, whereas partial localization is possible only in 10.7% of patients.

Theoretically, intraoperative neuromonitoring of the pelvic autonomous nerves (pIONM), could quantify intraoperative nerve injuries, while in parallel, contribute to the improvement of the patients' postoperative quality of life. Several pIONM techniques have been described, including intra-urethral and intra-vesical pressure measurements. However, it was found that intermittent neuromonitoring objectifies the macroscopic integrity assessment of the sacral plexus. Recently, a promising technique, based on the simultaneous electromyography of the IAS and bladder manometry was developed, with encouraging results. During pIONM, the surgeon delivers electric stimuli to the autonomic nerve structures through a hand-held stimulator. At the same time, electromyogram changes of the IAS and the external anal sphincter (EAS), alongside intravesical pressure gradients are assessed.

Intraoperative neuromonitoring has been evaluated in several experimental studies. In a recent study, intraoperative simulation of the inferior hypogastric plexus with a bipolar stimulator resulted to the appearance of a measurable and repeatable electromyographic signal from the IAS.