Rediscovery of forgotten structures inside mucosa of uterine tubes ‐ lymphatic lacunae‐ and their possible role in reproduction.

Abstract

Human uterine tubes are paired, muscular tubes of great mobility that measure about 12 cm in length. The uterine tube wall is composed of a mucosa, a muscular layer, and a serosa. Mucosa forms longitudinal mucosal folds and is lined with a simple columnar epithelium. In this poster presentation, we described in detail a neglected structure of uterine tubes, central lymphatic lacunae of mucosal folds and fimbriae. These lymphatic lacunae were first time described by German gynecologist Paul Kroemer in 1904. Dr. Kroemer, as a part of his habilitation, injected ink to visualize lymphatic spaces in the pregnant woman's ovarian tube, which he named as “Lymphbahnen”, that is “lymphatic channels”. In recent textbooks, we found only one note about these lymphatic lacunae inside fimbriae, and also we found no mention about these structures in Terminologia Histologica. The specimens from the uterine tubes were taken from 48 women (age from 21 to75, mean age 48.8 years) who underwent trans-abdominal or laparoscopic surgery - salpingectomy with or without hysterectomy. The study protocol was approved by the ethical committee of local hospital, and informed consent was obtained from all patients. Tissue samples from anatomically different parts of the uterine tubes (infundibulum with fimbriae, ampulla and isthmus) were fixed in formalin, embedded in paraffin, and 5 μm thick sections were used for hematoxylin and eosin staining and for immunohistochemistry. Primary antibodies were used to label and detect podoplanin D2–40, a relatively new and selective marker of lymphatic endothelia, and CD34 antigen, a universal marker of blood endothelial cells. For visualization of the histological sections by means of light microscopy, the LEICA DM2500 microscope was used. In the histological slides of uterine tubes, stained with hematoxylin and eosin, there are noticeable slits or gaps within the loose connective tissue of lamina propria of the mucosal folds. They are lined with one layer of squamous cells resembling endothelial cells and are devoid of content. These “empty spaces” are most prominent in fimbriae, but are still well recognized in mucosal folds of ampullary region. In the isthmus, they are least visible. They always run thru the central part of the fold, reminding with their histotopographical localization lacteals in the center of intestinal villi. Squamous endothelial cells that line these gaps in the connective tissue do not express CD34 antigen, what can be regarded as a proof, that they are not blood vessels nor blood sinusoids. However, they are positive on podoplanin (D2–40) – selective marker of lymphatic endothelial cells. As a result, we confirmed that in the center of every mucosal fold and in fimbriae of the uterine tubes are situated dilated lymphatic spaces, which are lined with simple layer of endothelial cells. As there is no mention on them in current Terminologia Histologica (2008), we propose the term “central lymphatic lacunae of tubal mucosal folds and fimbriae”. Remains a question, why these lacunae are only rarely (and unsatisfactory) described in the literature, as the visibility of these large spaces even with the routine hematoxylin and eosin staining is excellent. Many times, the structures we had been looking for, had been well seen on microphotographs, however, without any description. This confirms, that lymphatic lacunae are physiologically present in the mucosa of uterine tubes and that until now, they had been just neglected and overlooked. Ampullary region of human uterine tube in hematoxylin and eosin staining (lymphatic lacunae are visualised by red color) and visualisation of lymphatic endothelia with podoplanin-antibodies (and diaminobenzidine as brown chromogen) This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.