Azoospermia can be defined as the absence of spermatozoa in the seminal fluid and/or in the urine after ejaculation and can be subdivided into the obstructive and non-obstructive subtypes. Obstructive azoospermia (OA) represents only 15-20% of all cases of azoospermia and is characterised by the presence of a blockage, which does not allow the spermatozoa to make their way out in the seminal fluid.
In order to fully understand obstructive azoospermia, it is important to know the pathway spermatozoa have to take from the testicle in order to reach the ejaculate.
Spermatozoa are produced in the testicle and reach the epididymis through small tubules that join together to form a single larger tubule which coils on its own to form the body and tail of the epididymis itself. The full length of this tubule is around 7 meters. The epididymis is then connected to the prostate and the urethra through a conduit approximatively 40 cm long, which is called vas deferens. Before entering the urethra, the vas deferens joins the duct of the seminal vesicle to form the ejaculatory duct.
Prostate and seminal vesicles produce a thick whitish fluid, called seminal fluid, which mixes with the spermatozoa to form the semen.
Obstruction at any point can cause obstructive azoospermia.
According to the location of the blockage, obstructive azoospermia can be subdivided into:
1) Intra-testicular obstruction (15% of cases)
2) Epididymal obstruction (30-70% of cases)
3) Obstruction of the vas deferens (5-10% of cases)
4) Ejaculatory duct obstruction ( 3-5% of cases)
If the obstruction is intra-testicular or at the level of the head of the epididymis, surgical recanalisation is not possible and therefore intra-testicular sperm extraction (TESE) is the only solution to retrieve spermatozoa.
In case of obstruction of the epididymis, although sperm retrieval is possible with a percutaneous epididymal sperm aspiration (PESA), with a microsurgical epididymal sperm aspiration (MESA) or with a TESE, in many cases it is possible to perform a microsurgical reconstruction to bypass the obstructed site and allow the spermatozoa to flow back into the ejaculate. This complex microsurgical procedure is called tubulo-vasostomy and involves connecting the vas deferens with the body of the epididymis. Due to its complexity, success rate of this procedure is around 50%.
Obstruction of the vas deferens is in most cases secondary to previous vasectomy or inguinal hernia repair, and can be corrected with a vaso-vasostomy procedure. This microsurgical technique involves excising the obstructed segment of vas and connecting back together the two ends of the vas. Although complex, in expert hands this procedure has very high success rates.
Ejaculatory duct obstruction can be caused by the presence of stones inside the duct or by external compression caused by a midline prostatic cyst. Stones can be usually washed away flushing the seminal vesicles under ultrasound guidance while prostatic cysts can be resected endoscopically reliving the compression of the ejaculatory ducts. If the last portion of the ejaculatory ducts is obstructed, this can be resected off endoscopically with a procedure called transurethral resection of the ejaculatory ducts (TURED).
In conclusion, although in many cases of obstructive azoospermia testicular/epididymal sperm extraction represents the only solution for patients wishing to father a child, microsurgical reconstruction that allows to bypass the obstruction is possible and should be offered to carefully selected patients. If successful, these reconstructive procedures will allow the couple to father a child naturally.