A serial section study of visually normal posterior pelvic peritoneum from baboons (Papio cynocephalus, Papio anubis) with and without spontaneous minimal endometriosis

To determine if microscopic endometriosis exists in visually normal pelvic peritoneum from baboons with and without endometriosis. Observational histologic study at Institute of Primate Research, Nairobi, Kenya. Seventeen baboons including 13 adult females (5 with histologically proven endometriosis, 8 with a normal pelvis) and 4 juveniles (1 female and 3 males). Diagnostic laparoscopy with identification of visually normal pelvic peritoneum before euthanasia, followed by laparotomy with excision of a large area (at least 4×6cm or 24cm2 per animal, 408cm2 surface in all baboons) of this visually normal-appearing peritoneum. Presence of microscopic endometriosis (endometrial glands and stroma) in serial sections of visually normal pelvic peritoneum. Two adjacent glandular structures compatible with endometriosis were found in normal peritoneum obtained during menses from one female baboon without macroscopic disease. Microscopic endometriosis was not detected in the other female primates with or without macroscopic disease or in male animals. Microscopic endometriosis was found in only 1 of 14 female baboons (prevalence 7%; 95% confidence interval 0% to 33%) with visually normal pelvic peritoneum. These findings suggest that, with the paucity of human data available, more studies are needed before concluding that massive microscopic disease exists in visually normal-appearing peritoneum of women.