The epididymis is an elongated structure, posterolateral to testes, with head, body and tail regions.
The total length of the epididymis is usually 6-7 cm in length but it is tightly coiled and would measure 6 m if uncoiled 3.
The head is its largest and most recognisable part and is found at the superior pole of the testis. The head of the epididymis measures approximately 5-12 mm in length and may have a small projection called the appendix of the epididymis 3. The tail of the epididymis is found at the inferior pole of the testis 3.
Seminiferous tubules carry the sperm via tubuli recti into a dilated space within mediastinum testes which is known as rete testes. Rete testes drains into epididymis through 10-15 efferent ductules 1. Efferent ducts in the head of epididymis (globus major) unite to form a single duct (globus minor) in the body and tail region, which continues as the vas deferens.
See article: Testicular and scrotal ultrasound
Normal epididymis is iso-to-hyperechoic to the testes, with equal or less vascularity on color and spectral Doppler. The head of the epididymis is visualized superior and lateral to the testes, while the body and the tail are smaller with variable locations 2.
- T1 - epididymis has homogenously intermediate signal
- T2 - epididymis has hyperintense signal, with slightly lower signal than testes.
History and etymology
"Epididymis" derives from the Greek έπιδιδνμίς (έπί "upon" + δίδνμος "testicle"). Δίδνμοι (meaning "twins") was an older term for both testicles and ovaries. Galen originally used the term to refer to what we now call the tunica, and used the term "parastates" ("standing beside") for what we call the epididymus. Herophilus may be the first to use it in the current sense.