**Core Concept**
The deep perineal space is a fascial compartment located within the perineum, containing vital structures such as the external urethral sphincter, membranous part of the urethra, and the dorsal nerves of the penis/clitoris. A tumor in this space can lead to compression or injury of these delicate structures.

**Why the Correct Answer is Right**
The external urethral sphincter is a key muscle that controls the flow of urine. Located in the deep perineal space, it is susceptible to injury from a growing tumor. The sphincter's integrity is crucial for maintaining urinary continence. Compression or damage to this muscle can lead to urinary incontinence or difficulty initiating urination.

**Why Each Wrong Option is Incorrect**
**Option A:** The superficial perineal space contains structures like the bulb of the penis and the ischiocavernosus muscle, which are less likely to be injured by a tumor in the deep perineal space.
**Option B:** The cavernous nerves are responsible for erectile function and are located in the pelvic plexus. While they are affected in certain urological conditions, they are not the primary structure at risk in a deep perineal space tumor.
**Option C:** The pudendal nerve, which arises from S2-S4, provides motor supply to the external anal sphincter and the perineal muscles. While it is an important nerve, it is not the most likely structure to be injured by a tumor in the deep perineal space.

**Clinical Pearl / High-Yield Fact**
When evaluating a patient with a perineal tumor, it's essential to assess the function of the external urethral sphincter to predict potential urinary complications. A weakened or non-functional sphincter can lead to significant morbidity.

**Correct Answer:** A. The external urethral sphincter.