‘Testis–epididymis dissociation’ in cryptorchidism and hydrocele: the tip of the iceberg of a persistent genital mesentery

Purpose To investigate whether testis–epididymis dissociation encountered in boys with cryptorchidism/hydrocele is related with an abnormal persistence of the fetal mesentery of testis and associated ducts. Methods We examined the morphology of peritoneal folds of the testis, epididymis, and vas deferens in 25 boys operated for unilateral cryptorchidism [inguinal ( n = 20), intrabdominal ( n = 5)] and 20 boys operated for unilateral communicating hydrocele. Findings were compared with the normally persisting genital mesentery of rats ( n = 30, both sides), a known animal model of the genital mesentery of human fetuses, as well as with the normal mature pattern of genital peritoneal folds in adult male cadavers ( n = 12, both sides). Rats before testis descent [aged 18 days ( n = 15)] served for comparison with boys with cryptorchidism, while rats after testis descent [aged 50 ( n = 15)] known to retain patent processi vaginales for comparison with boys with hydrocele. Results A well-developed genital mesentery, identical to the fetal-type genital mesentery in the rat, was documented in cryptorchidism and hydrocele. The peritoneum enveloped the testis, epididymis, and vas deferens, and formed wide ligaments between testis–epididymis, epididymis–vas deferens, and vas–posterior wall; processus vaginalis was patent in all cases. The testis–epididymis ligament was related with testis–epididymis distancing, the so-called testis–epididymis dissociation. On the contrary, genital mesentery had involuted in the adult male cadavers, except for a small portion of testis–epididymis ligament corresponding to the so-called sinus epididymis. Conclusion The testis–epididymis dissociation encountered in cryptorchidism/hydrocele is part of an anomalously persisting fetal-type genital mesentery.