Development, structure and function of the cranial suspensory ligaments of the mammalian gonads in a cross-species perspective; their possible role in effecting disturbed testicular descent.

The present review aims to present a perspectiveon a relatively unknown part of the mammalian internal genitalia: their cranial suspensory apparatus. This apparatus shows wide divergence of development when examined during the fetal period or during adulthood, in males or females, or in individuals across a variety of species. In rats and other mamalian species the apparatus undergoes a distinct patern of sexually dimorphic development and fetal testicular androgens are proposed to play a key role in this process. Extensive development of this suspensory apparatus in females is argued to be a part of the anatomical adaptations of the genital apparatus to support the internal genitalia throughout pregnancy, including the relatively enormous growth towards the time of parturition. Minor development of this apparatus in males is judged to be a part of the anatomical requirements allowing developing testes to become displaced from the dorsal abdominal wall during the first stage of testicular descent. Extensive development of this suspensory apparatus in males generally seems to hinder testicular descent. Accordingly, the apparatus is well developed in so-called testicond species which do not show testis descent as a part of their normal male genital development. Furthermore, arguments are adduced that inappropriate and extensive development in species with testis descent may be a key aetiological factor in the disturbance of this process. Diagnosis and treatment of human cryptorchidism might profit from including an analysis of the development and function of (remnants of) the cranial testicular and epididymal suspensory apparatus.