Unilateral monorchidism and cryptorchism. Clinical and biological findings useful in the differential diagnosis

: Eighteen prepuberal children with only one testis palpable in the scrotum were studied in order to review the clinical and endocrinological data useful for differentiating monorchidism from unilateral cryptorchidism. Compensatory testicular hypertrophy, high LH and FSH response to LH-RH (100 micrograms/1.73 m2) and well preserved Leydig cell function after HCG (5,000 IU/m2) should lead to the diagnosis of monorchidism, either both congenital or secondary to severe atrophy of the unpalpable testis. When these findings are lacking the diagnosis of unilateral cryptorchidism should be considered.