## **Core Concept**
The posterior urethra is a part of the male urethra that passes through the prostate gland and is surrounded by the internal urethral sphincter. Visualizing this area is crucial for diagnosing conditions such as benign prostatic hyperplasia (BPH), prostate cancer, and urethral strictures. Investigations for visualizing the urethra include cystoscopy, urethrography, and imaging studies like MRI.

## **Why the Correct Answer is Right**
The correct answer, **Cystoscopy**, is the best investigation for visualizing the posterior urethra. Cystoscopy involves inserting a flexible or rigid scope with a camera and light through the urethra into the bladder, allowing direct visualization of the urethral lumen, including the posterior urethra. This procedure can help identify abnormalities such as strictures, tumors, and prostatic enlargement. Cystoscopy is highly sensitive and specific for diagnosing urethral and bladder pathology.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Ultrasound is useful for assessing bladder and prostate size and evaluating urinary retention but does not provide direct visualization of the urethral lumen.
- **Option B:** Urethrography (or retrograde urethrography) can visualize the urethra, especially the anterior part, but may not provide detailed images of the posterior urethra, especially in the presence of obstruction.
- **Option D:** MRI can provide detailed images of the prostate and surrounding structures but is not typically used for direct visualization of the urethral lumen.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that cystoscopy is not only diagnostic but also therapeutic, as it allows for procedures like urethral dilation, stent placement, and biopsy of urethral or bladder lesions. Remember, cystoscopy requires careful patient selection and preparation, especially in men with urethral strictures.

## **Correct Answer:** . Cystoscopy