Anatomical Pitfalls of Excision of Deep Endometriosis Nodules of the Sciatic Nerve: A three-dimensional Reconstruction and Surgical Educational Video.

Study Objective: To highlight the anatomical keys to safely performing an excision of deep endometriosis nodules of the sciatic nerve DESIGN: We present a didactic video combining an anatomical three-dimensional reconstruction of the pelvis using the Anatomage table and a surgical dissection video of the removal of deep endometriosis nodules of the left sciatic nerve [1]. The patient's approval was obtained. The patient consented that this surgical video be used for publication.

Setting: Tertiary referral center.

Interventions: To reach this specific area, we must localize precise anatomical pitfalls [2,3]. Taking the external iliac vessels as an anatomical plane of reference, we can divide anatomical structures into lateral and medial. During the first step of the procedure, we open the latero-pelvic peritoneum covering the external iliac artery. This step allows the identification of the lateral anatomic keys. Lateral anatomic keys are represented by: (1) the genito-femoral nerve, an element which is superficially situated between the psoas muscle and external iliac artery, and (2) the obturator nerve (Video Still 1), which is deep and is located within the ilio-lumbar fossa. To enter it, a dissection between the psoas muscle and external iliac artery and vein must be performed. At this point, particular attention must be paid to the obturator artery that runs below the obturator nerve. In this fossa, the lumbosacral trunk is easily identified just below the obturator nerve; it lies at this level on the iliac bone. Then the opening of the posterior leaf of the broad ligament is realized. Therefore, we access the medial anatomic keys: (1) the ureter, and (2) the umbilico-artery trunk with the umbilical and uterine artery. In the opening of the posterior leaf, we can find the obturator nerve and lumbosacral trunk again. Finally, following the umbilical artery (that is the first branch of the internal iliac artery), we discover the internal iliac artery and vein. A very careful dissection of these vessels must be done to avoid big hemorrhages, which can be life-threatening [4-6]. In the plane below the internal iliac artery and vein, we access the sacral roots S1, S2, and S3 (Video Still 2), which join the lumbosacral trunk (lying on the piriformis muscle) to form the ischiatic nerve [7]. At this level, the ischiatic nerve exits through the infra-piriform foramen behind the ischiatic spine and sacrospinous ligament toward the gluteal area in an oblique way [8]. Two other elements may be seen: the pudendal nerve exiting the pelvis behind the sacrospinous ligament in a craniocaudal way and the posterior femoral cutaneous nerve. During this dissection, the autonomous system must be spared as usual to avoid functional sequelae.

Conclusion: Removal of deep endometriosis nodules of sciatic nerves is a challenging procedure. Because few surgeries are specifically dedicated to the sciatic area, the specific anatomy of the region is poorly taught and known. However, pelvic anatomical knowledge is indispensable to the safe removal of nodules of sciatic nerves. The main advantage of this anatomical 3D reconstruction is the possibility of visualizing the deep pelvic anatomy in a laparoscopic position. Surgeons must be aware of both somatic and autonomous pelvic nerve anatomy within the retroperitoneal spaces and the great vessels surrounding them.