corpus spongiosum

The corpus spongiosum is a single midline erectile body located ventral to the paired corpora cavernosa within the penile shaft. It encases the penile (spongy) urethra along its entire length, expanding proximally to form the bulb of the penis (fixed to the perineal membrane, associated with the bulbospongiosus muscle) and distally to form the glans penis, which caps the corpora cavernosa. Unlike the corpora cavernosa, the corpus spongiosum is surrounded by a thinner, more elastic tunica albuginea, allowing it to engorge with blood during erection without the high intracavernosal pressures seen in the cavernosa—this is clinically important because it keeps the urethra open for ejaculation despite penile rigidity. Vascular supply comes from the bulbourethral artery (branch of internal pudendal artery). Clinically, the corpus spongiosum is relevant in: (1) Priapism—typically involves the corpora cavernosa, sparing the spongiosum, which is why the glans often remains soft; (2) Urethral trauma/strictures, since the spongy urethra runs through it; (3) Hypospadias/epispadias, congenital anomalies related to urethral and spongiosum development; (4) Peyronie's disease, which primarily affects the tunica albuginea of the cavernosa rather than spongiosum; (5) Priapism classification (low-flow vs high-flow) relates to cavernosal, not spongiosal, hemodynamics. Understanding the distinct vascular and structural properties of the corpus spongiosum versus corpora cavernosa is tested on boards particularly in the context of erectile physiology, priapism, and urethral anatomy.