Very rarely the individual may experience an orgasm without expelling semen from the urethra. This can occur due to purely psychogenic problems in young men, linked to fears of producing a pregnancy or for other reasons. On other occasions, this problem may be due to disorders of the ejaculation mechanisms, generally nerve-related, lesions to the neck of the bladder or through taking certain drugs. This tends to happen after certain prostate surgeries or in surgeries performed during childhood on the neck of the bladder due to malformations in that region.
During normal ejaculation, the semen passes through the urethra while the neck of the bladder (internal sphincter) and the urinary sphincter (external sphincter) close. Subsequently, the latter opens and the semen is expelled through the meatus of the urethra. If these mechanisms fail the semen passes to the bladder (retrograde ejaculation) and is subsequently expelled with the urine.