Contribution to the origin and development of the appendices of the testis and epididymis in humans

Abstract

Hydatids, as appendices of testis or epididymis, were discovered by Morgagni in 1703 and 1705 and published by him in 1761. Hydatids are considered to be remnants of the cranial part of the Mullerian duct (MD), Wolffian duct (WD), or mesonephric tubules. They are localized as sessile or pedunculated appendices at the cranial pole of testis and at the head of epididymis, or at analogous organs in women. The clinical relevance is known: acute scrotum with torsion of appendices, or metaplasia. However, little is known about the embryological development of hydatids. Therefore, we studied the origin and development of appendix testis (AT) and appendix epididymidis (AE) in human embryos from stage 14 (Carnegie Collection), 6.5 mm GL, 32 days, to fetuses of 170 mm, 17th week. Light and scanning-electron microscopy as well as plastic reconstructions from serial sections of the cranial parts of MD and WD reveal that hydatids already form during regression or transformation of the ducts. At stage 18, 15-16 mm GL, 44 days, the cranial parts of MD and WD exhibit morphological features that give a preview on the definite form and position of later appendices. In fetuses from 45 mm GL, ninth week onward, we found anlagen of pedunculated hydatids (AE) deriving from the ampullated cranial end of the WD, which in many cases opened into the coelomic cavity. The unpedunculated AT derived from the persisting funnel region of the MD. The development of duct-independent, accessory appendices was observed. We paid special attention to a pedunculated hydatid in a fetus of 120 mm, 14th week, and the cranial regressing WD. A classification of hydatids is presented. Photographs and histological sections of (sessile) appendices testis (AT), and (pedunculated) appendices epididymidis (AE) with torsion of stalks exhibit the final forms and positions of hydatids in adult.

Structural analysis of testicular appendices in patients with cryptorchidism

“…Another hypothesis suggests that the surface epithelium, subepithelial capillaries and lymphatic vessels of testicular appendices form a functional unit (8). Some studies have analyzed the embryology (9) and structure of the testicular and epididymal appendices (3,10).…”

Differential expression of androgen and estrogen receptor of appendix testis in patients with descended and undescended testes

“…The exact role of this hydatid is unclear, there are only a few reports that discuss the possible functions of AT in humans. Holstein assumed that the AT controlled the amount of serous fluid within the space of the tunica vaginalis, 2 while another theory suggested that the epithelial layer together with subepithelial capillaries and lymphatic vessels form a functional unit 3…”

Complete androgen insensitivity without Wolffian duct development: the AR‐A form of the androgen receptor is not sufficient for male genital development

“…The epididymides show typical characteristics of highly coiled ducts lined by tall columnar cells, whereas the vasa deferentia have a slightly folded mucosa and a thick muscular coat consisting of three layers 12 . These androgen‐stimulated structures are distinct from Wolffian and Müllerian remnants, which can be found in both sexes and are thought to represent vestigial parts of the common genital ducts that have failed to regress completely 15 . Severe AIS is associated with AR mutations that retain very low but significant residual activity, sufficient to cause male differentiation only in the local environment surrounding the testis, where testosterone concentrations are estimated to be at least 100 times higher than in the circulation 12,16 …”