This is the failure of the testis to descend normally into the scrotum. Descent
may be arrested at any point along the normal path from abdomen to upper scrotum.
About 4% of newborn, full-term males have a cryptorchid testis, but in the
majority the testis descends into the scrotum so that incidence drops to less
than 1% in adults. The condition is commonly unilateral but may be bilateral
in about 25% of cases and is slightly more common on the right. The reasons
for the failure of the testis to descend are not known.
The cryptorchid testis undergoes progressive atrophy and is small in size
and firm in consistency. Histologically, the changes range from a reduction
in number of germ cells to complete absence of germ cells with hyalinization
and thickening of the seminiferous tubular basement membrane and stromal fibrosis.
Finally, the tubules appear as hyalinized cords of connective tissue with
surrounding prominent basement membranes. Leydig cells appear in prominent
nodules in the interstitium. The scrotal testis of patients with unilateral
cryptorchidism may show similar histologic changes.
There are two important sequelae of this condition. Failure of spermatogenesis
in the cryptorchid testis due to the high temperature of the non-scrotal tissues
and reduction in germ cells in the scrotal testis result in infertility. More
ominous is the increased risk for development of testicular germ cell tumors
(see below). The higher the cryptorchid testis is arrested in its descent,
the greater the risk of subsequent germ cell tumor. Orchiopexy (surgical fixation
of the testis in the scrotum) should be performed early. The protective effect
of orchiopexy is difficult to evaluate, as there have been reports of germ
cell tumors arising in testes surgically positioned in the scrotum at an early
age. However, most studies that early orchiopexy reduces the risk of germ
cell tumor. For this reason, an undescended testis discovered in an adult
should be removed.