This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
[{'content': 'Semen analysis of a young man who presented with primary infertility revealed low volume, fructose negative ejaculate with azoospermia. Which of the following is the most useful imaging modality to evaluate the cause of his infertility? \nSelect and explain. \nA. Colour duplex ultrasonography of the scrotum, B. Transrectal ultrasonography, C. Retrograde urethrography, D. Spermatic venography', 'role': 'user'}, {'content': 'Answer: B \nExplanation: First lets briefly review the anatomy of male internal genitalia\nSperms are produced in testes and then stored and mature within the epididymis. Vas deferens carries the sperms from epididymis to the urethra where they open by separate openings into the prostatic urethra. Just before opening each vas deferens is joined by ducts of seminal vesicles. Vas deferens and seminal vesicle ducts join to form the ejaculatory duct.\nThe secretions of seminal vesicles form a large part of seminal fluid and contain fructose and a coagulating enzyme called the vesiculase.\n\nNow coming to the question.\n\nSemen analysis forms an important part of infertility assessment.\nLow ejaculatory volume is caused by\nretrograde ejaculation into the bladder or\nobstruction of the vas deferens or the ejaculatory duct\nAzoospermia may be seen in\ntesticular failure or\nobstruction of vas deferens\nAbsence of fructose suggests\nseminal vesicles agenesis or obstruction.\nA semen that is low in volume with azoospermia and absence of fructose suggests → either obstruction of the ejaculatory ducts or congenital absence of the vas deferens and seminal vesicles.\nThe anatomy of the vas deferens & seminal vesicles can be investigated by vasography (where contrast medium is injected into the vas deferens) or TRUS (Trans rectal ultrasonography), however TRUS is superior to vasography and is the investigation of choice.\nAlso know\nSemen specimen should be obtained following at least 3 days of abstinence and examined within 1 to 2 hrs. At least 2 specimens are examined several weeks apart.', 'role': 'assistant'}]