Semen analysis of a young man who presented with primary infeility revealed low volume, fructose negative ejaculate with azoospermia. Which of the following is the most useful imaging modality to evaluate the cause of his infeility?
Low semen volume and absence of fructose suggest a problem with the seminal vesicles, which normally contribute most of the seminal fluid and fructose. Azoospermia means no sperm in the ejaculate. If the seminal vesicles aren't contributing, maybe there's a blockage in the ejaculatory ducts or absence of the vas deferens.
The most useful imaging modality would be something that can visualize the seminal vesicles and vas deferens. Transrectal ultrasound (TRUS) is commonly used for this. It can detect cysts, obstruction, or absence of the vas deferens. MRI might also be used but is less specific for the seminal vesicles.
The options aren't listed here, but if the correct answer is TRUS, then the other options like plain X-ray, CT, or scrotal ultrasound would be incorrect. CT isn't typically used for this. Scrotal ultrasound checks the testes, not the seminal vesicles.
Clinical pearl: Remember that fructose is a marker for seminal vesicle function. Its absence points to a problem in the seminal vesicles or their ducts. TRUS is the go-to imaging here.
**Core Concept**
This question assesses the evaluation of male infertility, specifically azoospermia with fructose-negative ejaculate. The absence of fructose indicates seminal vesicle dysfunction or obstruction, while low volume suggests retrograde ejaculation or ductal blockage. Imaging must target the ejaculatory ducts and seminal vesicles.
**Why the Correct Answer is Right**
**Transrectal ultrasound (TRUS)** is the gold standard for visualizing the seminal vesicles, ejaculatory ducts, and prostate. It detects cysts, strictures, or congenital absence (e.g., congenital absence of the vas deferens, CAVD). In fructose-negative azoospermia, TRUS can identify seminal vesicle atrophy or obstruction, guiding further management like surgical repair or assisted reproductive techniques.
**Why Each Wrong Option is Incorrect**
**Option A:** Plain X-ray lacks resolution for soft tissue structures like seminal vesicles.
**Option B:** CT imaging is less sensitive than TRUS for seminal tract abnormalities and exposes patients to radiation unnecessarily.
**Option C:** Scrotal ultrasound evaluates testicular pathology (e.g., varicocele) but not the ejaculatory ducts or seminal vesicles.
**Clinical Pearl / High-Yield Fact**
Fructose is secreted by the seminal vesicles. Its absence in semen confirms their dysfunction or absence. **TRUS** is non-invasive and highly specific for diagnosing obstructive causes of azoospermia, making it essential in infertility workup.
**Correct Answer: C. Transrectal ultrasound**