Laparoscopic morphological aspects and tentative explanation of the aetiopathogenesis of isolated endometriosis of the sciatic nerve: a review based on 267 patients
Authors: Possover M 
Published: January 2022

Background: Endometriosis of the sciatic nerve (ESN) is considered a rare disease. How can endometriosis develop within the sciatic nerve; a structure which has nothing in common with the uterus either anatomically or functionally, and why it occurs in the absence of any retroperitoneal/parametric endometriosis, is unknown. A better understanding of the pathophysiology of this enigmatic disease may improve its diagnosis and therapy.

Materials and Methods: From a pool of 452 patients operated for ESN, only patients with “isolated” endometriosis of the sciatic nerve” confirmed at laparoscopy were included in this study. Patients with suspicion of ESN by extension from a parametric, ovarian or other intraperitoneal deeply infiltrating endometriosis were excluded from this study.

Main outcome measure: All information acquired during the preoperative patient’s medical history and clinical examination were collected and compared with the morphological aspects of the disease observed by the laparoscopic treatment. Patients were classified into three groups according to the time interval between the onset of sciatic pain and the time of surgery: less than 1 year (Group 1), between 1 and 3 years (Group 2), and more than 3 years (Group 3).

Results: Two hundred sixty-seven consecutive patients were included in this study. In Group 1 (n=67), 76% of the patients presented with cyclical sciatica, without sensory or motor disorders of the lower limbs. Laparoscopic exploration found in the great majority of these patients only the presence of an isolated endometrioma in the nerve itself, the size of which was proportional to the time elapsed since the onset of pain. In Group 2 (n=83), pain had become constant in 91% of the patients with neurological disorders of the lower limb (foot drop, Trendelenburg gait, atrophied muscles) in about 30% of patients. Laparoscopic examination revealed, in addition to intraneural cystic lesions, a retroperitoneal fibrosis in more than 80% of the patients. In the third group (N=117), more than 80% of the patients presented with neurological disorders of the lower limb, with, on laparoscopic examination, massive retroperitoneal fibrosis with endometriomas in the nerve and adjacent pelvic wall muscles in all patients and an infiltration of the obturator nerve in 41% of patients.

Conclusions: The different morphologic aspects of ESN do not correspond to different forms of the disease, but obviously to one single disease at different stages of its evolution. ENS starts first with the development of an endometrioma within the sciatic nerve, then develops in a second step a perineural fibrosis that expands into the whole retroperitoneal space and finally involves surrounding anatomical structures. The ESN is a very particular pathology because it induces a completely new aspect on the pathogenesis of endometriosis: all hypothesis of implanted endometrial cells following retrograde menstruation, angiogenic spread, lymphogenic spread or the metaplasia theory cannot explain the pathogenesis of this disease. ESN obviously does not develop from “genital metastatic cells”. A possible hypothesis for explanation the pathogenesis of ESN, could consist in the development of endometriosis of the nerve from progenitor stem cells present within the nerve, pluripotent cells which, for an as yet unknown reason (possibly in connection with iterative inflammations and micro-damages of the nerve itself), mutate and proliferate to form endometriosis.