**Core Concept**
Transrectal ultrasonography (TRUS) is a valuable diagnostic tool for prostate cancer evaluation. It allows for the assessment of prostate gland dimensions, the detection of hypoechoic lesions, and the measurement of prostate-specific antigen (PSA) density. TRUS-guided biopsy is also an essential component of prostate cancer diagnosis.

**Why the Correct Answer is Right**
TRUS is most useful for assessing the local extent of prostate cancer, particularly in the evaluation of extracapsular extension (ECE) and seminal vesicle invasion. The ultrasound waves can accurately identify the prostate gland's boundaries and detect any irregularities in the gland's shape or texture. This information is crucial for determining the cancer's stage and guiding treatment decisions. The ability of TRUS to accurately measure prostate volume and detect hypoechoic lesions also makes it an essential tool for monitoring treatment response and detecting recurrent disease.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because TRUS is not primarily used for assessing lymph node involvement or distant metastases. While TRUS-guided biopsy can provide tissue samples for lymph node analysis, other imaging modalities such as CT or PET scans are more commonly used for this purpose.

**Option B:** This option is incorrect because TRUS is not typically used for evaluating the urethra or bladder. While TRUS can provide information on the prostate gland's proximity to these structures, dedicated imaging modalities such as urethrography or cystography are more suitable for assessing urethral or bladder pathology.

**Option C:** This option is incorrect because TRUS is not primarily used for assessing the pelvic floor muscles or rectal wall. While TRUS can provide information on the prostate gland's position and surrounding tissues, dedicated imaging modalities such as MRI or CT scans are more commonly used for evaluating pelvic floor or rectal wall pathology.

**Clinical Pearl / High-Yield Fact**
When using TRUS for prostate cancer evaluation, it is essential to perform a systematic biopsy protocol to ensure adequate tissue sampling and accurate cancer staging. A minimum of 12 biopsy cores, including samples from the peripheral zone and transition zone, should be obtained to increase the diagnostic yield.

**Correct Answer: A. Assessment of local extent of prostate cancer.**