The posterior urethra is best visualized by:
**Core Concept**
The posterior urethra is a part of the male urethra that extends from the prostate gland to the penile urethra. It is surrounded by the prostatic urethra and is an important structure in the diagnosis and treatment of urological disorders.
**Why the Correct Answer is Right**
The correct answer is **C. Retrograde urethrogram (RUG)**. This imaging technique involves injecting a contrast agent into the urethra and taking X-rays to visualize the urethral lumen and surrounding structures. RUG is particularly useful for visualizing the posterior urethra, as it can show any narrowing, strictures, or other abnormalities in this area. The contrast agent can also outline the prostate gland and bladder neck, providing valuable information for diagnosing conditions such as benign prostatic hyperplasia (BPH) or prostate cancer.
**Why Each Wrong Option is Incorrect**
**Option A:** Cystoscopy is a useful technique for visualizing the urethral lumen and surrounding structures, but it is not the best method for visualizing the posterior urethra. This is because the posterior urethra is located deep within the prostate gland and is difficult to access with a cystoscope.
**Option B:** Ultrasound is a useful imaging technique for visualizing the prostate gland and bladder, but it is not the best method for visualizing the posterior urethra. This is because ultrasound waves do not penetrate well through the dense tissue of the prostate gland, making it difficult to visualize the posterior urethra.
**Option D:** Computed Tomography (CT) scans can provide detailed images of the prostate gland and surrounding structures, but they are not typically used to visualize the posterior urethra. This is because CT scans are more useful for evaluating the extent of disease or trauma in the prostate gland, rather than visualizing the urethral lumen.
**Clinical Pearl / High-Yield Fact**
When performing a retrograde urethrogram, it is essential to use a high-viscosity contrast agent to minimize the risk of contrast agent extravasation into the surrounding tissues. This is particularly important in patients with a history of urethral trauma or stricture disease.
**Correct Answer: C. Retrograde urethrogram (RUG)**