Imaging of obstructive azoospermia
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Obstructive azoospermia represents approximately 10 % of cases of male hypofertility. It is classified according to the volume of ejaculate. When the latter is normal a proximal obstruction is suspected. Scrotal sonography can help to detect dilation of the epididymal head when clinical findings are equivocal. Ejaculatory duct obstruction (EDO) is suspected when the volume of ejaculate is low. The use of transrectal ultrasonography (TRUS) plays a major role in the investigation of these patients, and endorectal MRI is a very useful adjunct in selected cases. The most common cause of EDO is congenital bilateral absence of vas deferens, which is now thought to be a genital form of cystic fibrosis in 80 % of cases. Consequently, a definitive diagnosis must be made before any attempt at in vitro fertilization. TRUS accurately visualizes abnormalities of the caudal junction of the vas deferens and seminal vesicles, yielding a definitive diagnosis without scrototomy. Other causes of EDO are congenital cysts compressing the distal part of the ejaculatory ducts and inflammatory distal stenosis. The former are accurately identified by TRUS, but the latter give more or less marked signs of obstruction which are only of value in azoospermic patients with a low-volume ejaculate. More invasive imaging is required to diagnose partial obstruction of the ED. Surgical vasography is still the reference, but puncture of the seminal vesicles under TRUS guidance is an attractive alternative, as it permits aspiration of seminal fluid (to seek motile sperm) and vasography without scrototomy. Lastly, endorectal MRI well assesses the relationships between the proximal prostatic urethra and the posterior wall of the ejaculatory ducts, which need to be precisely known when endoscopic resection of the ejaculatory ducts is planned.
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