The rete ovarii is a complex network of tubules found within the ovary, an anatomical feature that has long puzzled scientists and medical professionals. This structure has historically been considered a vestigial remnant, a leftover from embryonic development with no clear purpose in adult females. Despite its often-overlooked status, the rete ovarii is a notable component of ovarian anatomy.
Anatomy and Location
The rete ovarii is characterized by its tubular, anastomosing, or interconnecting, structure. It is typically found within the hilum of the ovary, the region where blood vessels, nerves, and lymphatic vessels enter and exit the organ. The rete ovarii is composed of three distinct regions: the intraovarian rete (IOR), the connecting rete (CR), and the extraovarian rete (EOR).
Microscopically, the tubules are lined by epithelial cells. The intraovarian rete consists of squamous epithelial cells that form a fine network of thin, solid cell cords, approximately 1–3 cells thick. The extraovarian rete develops into a convoluted tubular epithelium with a dilated tip, and its cells are ciliated and capable of cellular trafficking. The connecting rete, which links the intraovarian and extraovarian regions, gradually acquires tubular epithelial characteristics by birth.
Developmental Origins
The rete ovarii originates during embryonic development from the mesonephric tubules, also known as Wolffian ducts. These structures are primarily associated with the development of the male reproductive system, where they differentiate into the rete testis, efferent ductules, and epididymis. In females, the mesonephric tubules largely regress, but the rete ovarii persists, highlighting its homologous nature to the rete testis in males. While the male pathway involves the production of Anti-Müllerian hormone (AMH) and testosterone, leading to Müllerian duct degeneration and Wolffian duct development, AMH is absent in female development, allowing the Müllerian duct to differentiate into the oviduct and uterus. The rete ovarii demonstrates how structures from shared embryonic origins can persist in different sexes, even if their functions diverge or become unclear.
Understanding Its Function
Historically, the rete ovarii was considered a vestigial structure with no significant function. This perspective stemmed from its apparent lack of an obvious purpose when first identified in 1870. For over a century, researchers primarily focused on the functionally active components of the ovary, often overlooking the rete ovarii.
More recent research, however, suggests that the rete ovarii may have a more active role than previously thought. Studies indicate it might communicate with the ovary by directing a flow of protein-packed fluids through its tubular structure. The extraovarian rete has been found to contain secreted proteins, some of which may be involved in ovarian function and homeostasis. It appears to be closely associated with vasculature and neuronal projections, suggesting it could act as a sensory appendage that responds to hormonal signals.
Clinical Considerations
The rete ovarii can occasionally be associated with certain clinical conditions. Rete ovarii hyperplasia, a benign overgrowth of the rete tubules, can occur. This proliferation involves irregularly sized, interconnected channels and glands within the rete. The rete ovarii has also been rarely associated with certain ovarian tumors, such as serous cystadenomas or sex cord-stromal tumors. Tumors arising from the rete ovarii may exhibit stromal luteinization or contain Leydig-like cells.