The thick portion of the tunica albuginea is known as which structure?

• A. Mediastinum Testis
• B. Capsule
• C. Septum
• D. Tunica Vasculosa

Answer: (A)

The thickened interior part of the tunica albuginea is the mediastinum testis. The tunica albuginea acts as the testis’s tough capsule, and at the posterior aspect it thickens into this central fibrous structure that runs along the inside of the testis. The mediastinum testis provides a backbone for the organ, housing the rete testis and the beginnings of the ductal system, and it helps organize the internal architecture by anchoring vessels and ducts. On ultrasound you’d recognize it as a bright, linear area along the posterior border that helps orient the testis. The other terms refer to different structures: the capsule is the outer covering, the septum are partitions between lobules, and the tunica vasculosa is the vascular layer beneath the capsule.