A testis that is not within the scrotum and does not descend spontaneously into the scrotum by four months of age (or corrected age for premature infants) is a cryptorchid testis. Most cryptorchid testes are undescended, but some are absent (due to agenesis or atrophy).

●True undescended testes have stopped short along their normal path of descent into the scrotum. They may remain in the abdominal cavity or they may be palpable in the inguinal canal (intracanalicular) or just outside the external ring (suprascrotal ). 

●Between 2 and 5 percent of full-term and approximately 30 percent of premature male infants are born with an undescended testis. 

●Cryptorchidism usually is an isolated finding. However, it may occur in association with endocrine disorders, genetic syndromes, and morphologic abnormalities.

●Clinical features of cryptorchidism include an empty and hypoplastic or poorly rugated scrotum or hemiscrotum . Inguinal fullness may be present. Most congenitally undescended testes descend spontaneously by four months of age. 

●Some testes that have fully descended in infancy will, later in childhood (typically between the ages of four and eight years), ascend to an undescended position. 

●The evaluation of cryptorchidism typically includes history and physical examination. Imaging and laboratory studies are not routinely warranted but may be necessary to exclude associated conditions. 

●The diagnostic approach to cryptorchidism depends upon whether the testis is palpable or nonpalpable.

•The diagnosis of a truly undescended testis can be made with history and examination if the testis is palpable in the inguinal canal or just outside the external ring, and has been in this position since birth. Unlike retractile testes, palpable undescended testes cannot be milked into a normal scrotal position and/or will not remain in a normal scrotal position if the cremasteric reflex is overcome. Palpable undescended testes are differentiated from ectopic testes by their position (intracanalicular or suprascrotal versus suprapubic, femoral canal, perineum, or contralateral scrotal compartment). 

•The major diagnostic considerations for a unilaterally nonpalpable testis include true undescended testis, absent testis, and ectopic testis. Surgical exploration is usually necessary to distinguish among these possibilities.

•The major diagnostic considerations for bilaterally nonpalpable testes include disorders of sex development (DSDs), true undescended testes, anorchia, and bilateral testicular atrophy. The diagnostic evaluation differs depending on age. 

●Phenotypically male newborn infants with bilaterally nonpalpable testes, unilaterally nonpalpable testis with hypospadias, or suspected DSD, including congenital adrenal hyperplasia, should be immediately referred to a multidisciplinary team for evaluation and initial management of possible DSD. Boys beyond the newborn period with bilaterally nonpalpable testes should be referred to a pediatric urologist for evaluation and/or exploratory surgery.

●Additional indications for referral to pediatric urologist may include:

•Congenital unilaterally nonpalpable testis or palpable incompletely descended testis (unilateral or bilateral); referral between 4 and 12 months of age is recommended

•Ascending testis in boys beyond infancy (whenever the examination change is noted)

•Palpable tissue in the scrotum that is thought to be an atrophic testis

•Difficulty differentiating between undescended, retractile, or ectopic testis (at any age)

From Up To Date: Undescended testes (cryptorchidism) in children: Clinical features and evaluation