Based on presence or absence of ducts or vas deferens obstruction, azoospermia can be classified into obstructive azoospermia and nonobstructive azoospermia. 

• Several conditions that interfere with spermatogenesis and reduce sperm production and quality can lead to azoospermia: Y-chromosome microdeletions in AZF locus, hormonal disfunction, cystic fibrosis syndrome, Klinefelter syndrome. In this situation sperm cells can’t develop in the testis and it is called nonobstructive azoospermia.

• Obstructive azoospermia may be due to the following reasons: congenital bilateral absence of vas deferens, obstruction of ejaculatory and epididymal ducts, atresia of the seminal vesicles, various infections of the genitourinary tract resulting in obstruction or pelvic and inguinal procedures leading to a complete blockage such as a bilateral vasectomy. In obstructive azoospermia, spermatogenesis is often normal because in this situation sperm cells have opportunity to be developed but not to be delivered from testis.

There are different procedures to collect sperm from the testes: testicular sperm aspiration (TESA) and testicular sperm extraction (TESE). TESA samples are obtained with a wide-bore needle pushed percutaneously into the testis. TESE is an open technique that removes several pieces of testicular tissue. The combination of ICSI together with various testicular sperm retrieval techniques gives promising opportunities for these patients.

TESE is usually performed under local or general anesthesia as a biopsy of seminiferous tubules and their examination under a microscope in the laboratory to confirm the presence of sperm cells. Using fine-needle dissection or enzymatic processing the sperm cells are identified and separated from seminiferous tubules and surrounding tissue. The majority of these retrieved sperm cells are nonmotile but there is a special treatment with pentoxifylline to activate their motility.

Searching for the best spermatozoon can take several hours depending on degree of sperm amount and etiology of testicular failure. Published reports of successful IVF with azoospermia ranges from 7% to 45% of sperm existence due to different clinical diagnosis. If there are no sperm cells present in the sample, repeated sperm aspiration can be performed, on the same or opposite testicle. The intraoperatively retrieved sperm may be used immediately or cryopreserved for the future use.