Sometimes sperm is not present with ejaculation or a man may not be able to ejaculate. This can be due to problems in sperm production itself or due to obstructions of the flow of semen during ejaculation.
There are a variety of reasons why this may be the case, such as congenital anomalies, an infection, trauma, or injury.
There are many techniques possible to retrieve sperm, such as Penile Vibratory Stimulation (PVS), Electroejaculation (EEJ), Testicular Sperm Extraction (TESE), Testicular Sperm Aspiration (TESA), Microsurgical Epididymal Sperm Aspiration (MESA), or Percutaneous Epididymal Sperm Aspiration (PESA).
After sperm has been retrieved successfully, the sperm will typically be used for In Vitro Fertilization (IVF), Intracytoplasmic Sperm Injection (ICSI) or Intrauterine Insemination (IUI), among other artificial insemination procedures.