1 Anatomical considerations on pelvic intraoperative neuromonitoring F. Aigner 1 , R. Hörmann 2 , W. Kneist 3 , E. Brenner 2 , H. Fritsch 2 1 Department of Visceral, Transplant and Thoracic Surgery, Innsbruck Medical University, Austria, felix.aigner@i- med.ac.at 2 Division for Clinical and Functional Anatomy, Department of Anatomy, Histology and Embryology, Innsbruck Medi- cal University, Austria 3 Department of General, Visceral and Transplant Surgery, University Medicine of the Johannes Gutenberg-University Mainz, Germany Abstract Introduction: The aim of this clinical-anatomical overview is to provide a roadmap to pelvic neuroanatomy and poten- tial sites of iatrogenic injury for pelvic intraoperative neuromonitoring during low anterior rectal resection and abdom- ino-perineal excision. Methods: Data on pelvic neuroanatomy were derived from PubMed database and own investigations. Results: Five regions of potential nerve injury can be defined (1. Superior hypogastric plexus, 2. Hypogastric nerves, 3. Inferior hypogastric plexus and pelvic splanchnic nerves, 4. Inferior neurovascular bundles to the rectum and urogenital organs, 5. terminal pudendal nerve branches). Conclusion: Innovative techniques like pelvic intraoperative neuromonitoring and improvements in laparoscopic sur- gery enable the colorectal surgeon to detect the complex neural network and verify internal anal sphincter and urogenital function. The minimal invasive bottom-to-top approach may offer further insights. 1 Introduction Functional disorders of the pelvic floor after resections in the small pelvis are a matter of debate and often under- estimated according to the complex and still not fully un- derstood pelvic floor neuroanatomy. Any of the three con- nective tissue compartments of the pelvis (anterior, middle and posterior) can be affected with various clinical presen- tations (faecal incontinence, outlet obstruction, sexual and bladder dysfunction). Damage to the autonomic nerves close to the pelvic floor (i.e. the levator ani muscle) during ultralow rectal resection means damage to the extrinsic au- tonomic innervation to the rectum and consequently defe- cation disorder (the so-called low anterior resection syn- drome [1]. A novel two-dimensional pelvic intra-operative neuromonitoring (2D-pIONM) system based on electric neurostimulation under simultaneous electro-myography of internal anal sphincter and cystomanometry was recent- ly introduced to laparoscopic pelvic surgery for identifica- tion and verification of functional autonomic nerve integri- ty [2]. Within the BMT focus session "Assistance in pelvic sur- gery for nerve protection (pIONM)" the present study aimed to provide a roadmap to the complex pelvic neuro- anatomical topography and potential sites of iatrogenic in- jury for 2D-pIONM during low anterior resection of the rectum and abdomino-perineal excision. 2 Methods Data on pelvic neuroanatomy were derived from PubMed database and own investigations [3]. The bodies were do- nated by people who had given their informed consent for their use for scientific and educational purposes prior to death [4]. All cadavers were preserved using arterial injec- tion of an alcohol-glycerine solution and immersion in phenol in water for one to three months. Macroscopic ex- tended dissection enabled visualisation of the different anatomical layers, muscular and neurovascular structures as well as connective tissue of the posterior pelvic com- partment. The specimens were taken from the dissecting course and showed no sign of anorectal abnormalities. 3 Results The hindgut is innervated autonomously by the sympathet- ic and parasympathetic nervous systems [5]. Traditionally, the latter comprises the splanchnic branches of the vagus nerve as far as the left colic flexure. From there the para- sympathetic innervation of the gut is provided by the pel- vic parasympathetic part, with the pelvic splanchnic nerves forming the superior and inferior hypogastric plexus. Re- cent neuroanatomical investigations based on novel meth- ods such as computer-assisted anatomic dissection “CAAD” and immohistochemical staining revealed that