**Core Concept**
The membranous urethra is a short, constricted segment of the urethra located within the deep perineal pouch. A membranous urethral rupture leads to bleeding from the injured urethra, which accumulates in the surrounding space.

**Why the Correct Answer is Right**
The deep perineal pouch is a fascial space located between the perineal membrane (inferiorly) and the urogenital diaphragm (superiorly). When the membranous urethra ruptures, blood collects in this space due to the anatomical confinement. The urogenital diaphragm, which includes the external urethral sphincter and the deep transverse perineal muscles, forms a boundary around the deep perineal pouch. This anatomical arrangement leads to the accumulation of blood in the deep perineal pouch following a membranous urethral rupture.

**Why Each Wrong Option is Incorrect**
**Option A:** Ischiorectal fossa - This is a potential space located between the obturator internus muscle and the anal canal, not directly related to the membranous urethra.

**Option C:** Superficial inguinal region - This area is located in the lower abdominal wall and is not directly associated with the deep perineal pouch or the membranous urethra.

**Option D:** Pelvic diaphragm - The pelvic diaphragm consists of the levator ani and coccygeus muscles, which form the floor of the pelvis. While it is a significant anatomical structure, it is not directly related to the accumulation of blood following a membranous urethral rupture.

**Clinical Pearl / High-Yield Fact**
It is essential to recognize the anatomical relationships between the membranous urethra and the surrounding structures. A thorough understanding of these relationships can aid in the diagnosis and management of urethral injuries.

**Correct Answer:** ✓ Correct Answer: B. Deep perineal pouch