Absence of sperm in ejaculate. Obstructive Azoospermia: The result of obstruction in either the upper or lower male reproductive tract (epididymis, vas deferens, seminal vesicles or ejaculatory ducts). Sperm production may be normal (which may be verified through testicular biopsy), but the obstruction is preventing the sperm from being ejaculated. Some causes of obstructive azoospermia are vasectomy, congenital absence of vas deferens, scarring from past infections, and hernia operations. Non-obstructive Azoospermia: Severely impaired or non-existent sperm production. Some sperm may be found and extracted directly from the testicles.
A complete absence of sperm (spermatozoa) in the semen. Detectable only by performing a sperm count, as semen looks the same whether it contains sperm or not. Due either to an obstruction (usually in the epididymis or vas deferens), and called obstructive azoospermia, or to failure of sperm to form or to mature in the testis (called maturation arrest). See also spermatogenesis and testicular sperm extraction (TESE).