Relationship between endometriotic foci and nerves in rectovaginal endometriotic nodules

The histological relationships between fibrotic tissue, endometriotic foci and nerves in the rectovaginal septum endometriotic or adenomyotic nodule were studied. This is considered to be one of the most severe forms of deep endometriosis. Masson's trichrome staining for fibrosis detection and immunohistochemistry with the S100 monoclonal antibody for nerve detection were performed in 28 rectovaginal endometriotic nodules from patients presenting with severe dysmenorrhoea and deep dyspareunia (23 patients with no other endometriotic location or potential cause of pain at laparoscopy and ultrasonography; five patients with multiple pelvic endometriotic localizations and other potential causes of pain at laparoscopy). Patients were allocated to two groups on the basis of their preoperative pain scores for pelvic pain, dysmenorrhoea and deep dyspareunia (group 1, score >7; group 2, score < or =7). For each symptom, the mean number of nerves and endometriotic lesions per high-power field and the mean largest diameter of the lesions were not statistically different in groups 1 and 2. The mean percentages of nerves located within the fibrosis of the nodule and within endometriotic lesions were significantly higher in group 1 than in group 2. Among nerves located within endometriotic lesions, there was a significantly higher proportion showing intraneurial and perineurial invasion by endometriosis in group 1 than in group 2. In rectovaginal endometriotic nodules, there was a close histological relationship between nerves and endometriotic foci, and between nerves and the fibrotic component of the nodule. We postulate that such topographical relationships could at least partially explain the strong association between this lesion and pain.